Introduction of IMETU

Publications in 2002

1. Semiconductor Device and Physics

Study of Anisotropic Etching of (100) Si with Ultrasonic Agitation

Jing Chen, Litian Liu, Zhijian Li, Zhimin Tan

Qianshao Jiang, Huajun Fang, Yang Xu, Yanxiang Liu

Sensors and Actuators A, v96, n2-3

2 High precision bulk micromachining based on wet anisotropic etching of silicon is essential for the fabrication of MEMS devices. For the most commonly used KOH and TMAH anisotropic etching, ultrasonic agitation has been introduced to reduce the surface roughness and improve the etching uniformity. Etching characteristics of (100) Si have been studied and compared with that using magnetic stirring and that using no agitation. Smooth pyramid-free surfaces were obtained with the uniform etching depth within the resolution of 1μm on the same wafer being achieved at the same time. The results reveal that the ultrasonic agitation is a very efficient way to achieve smooth, defect-free silicon surface with high dimensional uniformity on the whole wafer.

Precision bulk micromachining based on KOH anisotropic etching using ultrasonic agitation

CHEN Jing LIU Li-tian LI Zhi-jian TAN Zhi-min

JIANG Qian-shao FANG Hua-jun XU Yang LIU Yan-xiang

Chinese Journal of Semiconductors， v23, n4

2 Production of smooth, defect-free anisotropic etched silicon surface with high dimensional uniformity patterned on the whole wafer is essential for the fabrication of MEMS devices. For the most commonly used KOH anisotropic etching, ultrasonic agitation has been introduced to reduce the surface roughness and improve the etching uniformity. Etching characteristics of (100) Si have been studied and compared with that without agitation source. Smooth pyramid-free surfaces were obtained with the uniform etching depth within the resolution of 1μm on the same wafer being achieved at the same time. The results reveal that the ultrasonic agitation is a very efficient high precision bulk micromachining approach.

SINGLE-CHIP CONDENSER MINIATURE MICROPHONE WITH A HIGH SENSITIVE CIRCULAR CORRUGATED DIAPHRAGM

Jing Chen, Litian Liu, Zhijian Li, Zhimin Tan, Yang Xu and Jun Ma

Technical Digest of the 15th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2002), Jan. 2002, Las Vages, Nevada, USA

2 A novel single-chip condenser miniature microphone with a circular corrugated diaphragm for residual stress releasing has been proposed, fabricated and tested. The condenser microphone consists of a rigid single-crystal backplate and a flexible circular corrugated diaphragm using induced couple plasma (ICP) etching. An electrostatic-structural coupling finite element analysis(FEA) was performed for design optimization. A sensitivity of 40mv/Pa up to 15KHz has been achieved under a low bias voltage of 14V, which is among the best in the presented reports.

Comparative Studies of Novel Capacitive Transducers with Non-Planar Diaphragms

Jing Chen, Litian Liu, Zhijian Li

Proceedings of the 5th International Conference on Modeling and Simulation of Microsystems (MSM 2002), Apr. 2002, CA, USA

2 Novel single-chip fabricated condenser structures with corrugated diaphragms for residual stress releasing have been proposed and simulated. An electrostatic-structural coupling FEM analysis has been performed to fully reveal the nonlinear relationship of output electrical signal with respect to input mechanical change. The influence of various nonlinear effects on the performance of transducers is investigated. Two typical corrugation layouts are studied. Numerical results have shown that the round structure was promising with its potential of high sensitivity, while the squared one was superior in the low-voltage applications. The ill effects of these variations can be reduced by delicate design and adjusting of corresponding processes.

A novel piezoelectric based RF BAW filter

Peng Cong, Tianling Ren, Litian Lu

Proceedings of the 5th International Conference on Modeling and Simulation of Microsystems (MSM 2002), Apr. 2002, CA, USA

2 A novel structure of piezoelectric based RF passband bulk acoustic wave (BAW) filter is fabricated using surface micromachining. The solutions of the wave equation for the electrode-piezoelectrics-electrode sandwich structure on support film in the BAW RF resonators are presented. Based on the solutions, a new method to adjust the frequency of the filter is given.

RF-MEMS BAW filter using surface micromachining

PENG CONG, TIAN-LING REN, JIAN-SHE LIU, LI-TIAN LIU

Integrated Ferroelectrics, 2002. (Accepted)

2 RF-MEMS bulk acoustic wave (BAW) filter using surface micromachining is successfully achieved using PZT as the piezoelectric layer. The resonant frequency is adjusted by changing the thickness of the SiO2 film on the top of the upper electrode. By etching the sacrificial porous silicon (PS) layer, the suspended structure is formed. This structure is able to eliminate the influence of the thick support film to the filter, and to improve the IC process compatibility and quality of the filter. Each resonator forms a self-supporting structure, so that the cross-talk between resonators with different frequencies will be dramatically reduced. In addition, dry-etching processes are used to improve the quality of the device. It is found that reactive ion etching (IRE) could be used to etch PZT/PT and platinum with a rate of 200 and 100 Å/min respectively using HCFC-124 as the etching gas.

Design of RF-MEMS BAW filter using surface micromachining

CONG Peng LIU Yanxiang REN Tianling LIU Litian

International Conference on Technology(ISTC 2001), Proceedings of SPIE Vol. 4414, p414-417

2 A novel structure of front end passband bulk acoustic wave (BAW) filter using surface micromachining is designed. The advantages and disadvantages of fabricating BAW RF filter using surface and bulk micromachining are discussed. The analytical solutions of the wave equation for the electrode-piezoelectrics-electrode sandwich structure on support film in the BAW RF resonators are presented.

Study of BAW Filter Using Surface Micromachining

Cong Peng Liu Yanxiang Ding Yong Xu Yang Ren Tianling Liu Litian

2001 6th International Conference on Solid-State and Integrated Circuit Technology Proceedings, Vol. 2, (C6.24)

2 A novel structure of front end passband bulk acoustic wave (BAW) filter using surface micromachining is designed. The advantage and disadvantage of fabricating BAW RF filter using surface and bulk micromachining are discussed. Porous silicon (PS) is used as a thick sacrificial layer. The process flow for fabricating BAW filters is given.

Novel BAW Filter Using Surface Micromachining

CONG Peng, REN Tianling, LIU Jianshe, LIU Litian

Journal of Tsinghua University (English Version), 2002. (Accepted)

2 Abstract: Nowadays, the major type of BAW is fabricated by bulk micromachining technology. This method has several disadvantages. A novel structure of front end passband bulk acoustic wave (BAW) filter using surface micromachining is proposed in this paper. The process flow for fabricating the BAW filters is given. Porous silicon (PS) is used as a thick sacrificial layer and the details of the method are discussed. The novel structure is helpful to eliminate the influence of the support film to the filter, and to improve the VLSI compatibility as well as quality of the filter. The cross-talk between resonators with different frequencies could be dramatically reduced by using resonators with a self-supporting structure.

FABRICATION OF A SUSPENDED RF-MEMS INDUCTOR WITH POROUS SILICON AS SACRIFICIAL LAYER

Ding Yong, Liu Zewen, Liu Litian, Li Zhijian

Pacific Rim Workshop on Transducers and Micro/nano Technologies, p43-46，July 22-24, 2002, Xiamen, China

2 A technology to fabricate suspended MEMS inductor for RF circuits is presented. Porous silicon (PS) is used as sacrificial layer, and SiO2 film is used as support membrane. During the process, TMAH solution with Si powder and (NH4)2S2O8 is used to remove the PS layer through small etching holes with no influence on the uncovered Al in the devices. A suspended inductor structure with the designed inductance of 4nH is realized using this technology. The fabrication is proved to be reliable.

Porous silicon surface micromachining process for suspended RF-MEMS application

DING YONG, LIU ZEWEN, LIU LITIAN, LI ZHIJIAN

Microsystem Technologies

2 A porous silicon(PS) surface micromachining technology for suspended RF-MEMS device fabrication is proposed. Using PS as sacrificial layer and SiO2 film as support membrane suspended metallic structure can be realized. The suspended structure size is 450×425μm2. To avoid any damage of the Al structure during the process, TMAH solution with Si powder and (NH4)2S2O8 is used to remove the PS layer through small etching holes. A suspended inductor structure is realized to demonstrate this technology.

An Uncooled Microbolometer Infrared Detector based on Polycrystalline Silicon Germanium Thin Film

Liang Dong, Rui-Feng Yue, Li-Tian Liu

International Journal of Nonlinear Sciences and Numerical Simulation，vol3, nos.3-4, 2002

2 This paper reports an uncooled microbolometer infrared detector with polycrystalline silicon-germanium (poly-Si0.7Ge0.3 ) thermistor as the active element. Using the anisotropic etching technique, the poly-Si0.7Ge0.3 thermistor is formed on a two legs supported microbridge suspended on a silicon substrate to decrease the thermal conductance. The dependences of the resistance and the temperature coefficient of resistance on temperature are described. The characteristics of the detector are investigated to infrared radiation in the spectral region of 8-14μm at an operation temperature of 296K. Measurements and calculations show that at a chopper frequency of 30Hz, the detector provides a peak responsivity of 30,000V/W, a peak detectivity of 1.68×109cmHz1/2/W and a thermal response time of 13.2ms.

Electrical Properties of Boron and Phosphorus Doped Polycrystalline Silicon Germanium Films

Liang Dong, Rui-Feng Yue, Wang Yan, Wen-Tao Huang, Li-Tian Liu

International Journal of Nonlinear Sciences and Numerical Simulation，vol3, nos.3-4, 2002

2 In this paper, the electrical properities of boron and phosphorus doped polycrystalline silicon germanium (poly-Si1-xGex) films with Ge mole fractions up to 0.51 are presented. Resistivity, Hall mobility and effective carrier concentration as a function of Ge mole fraction are discussed. Decreasing with the increase of Ge mole fraction, the resistivity of boron doped poly-Si1-xGex film is substantially lower than that of equivalently doped poly-Si film due both to higher levels of boron activation and higher hole mobility. The resistivity of phosphorus doped poly-Si1-xGex film is similar to that of equivalently doped poly-Si film and decreases slightly for Ge mole fraction below 0.4, but increases considerably for higher Ge content (x>0.4) because of a significant reduction in phosphorus activation. To achieve the same resistivity, lower annealing temperature, as well as lower implant dose is required for boron doped poly-Si1-xGex film than for poly-Si film, which makes p-type poly-Si1-xGex film an alternative to p-type poly-Si film.

Study of Bi2Ti2O7-Based Metal-Ferroelectric-Semiconductor (MFS) FET

Tian-ling Ren，Wu-quan Zhang，Chun-xiao Li,et al.

Integrated Ferroelectrics，v40，n1-5，2001，p1617-1622

2 P-channel metal-ferroelectric-semiconductor field-effect-transistors (MFSFET’s) and MFS capacitors using Bi2Ti2O7(BTO)/Si(100) structures were fabricated. The film stoichiometry and structure lattice are verified using X-ray energy dispersion analysis (EDAX) and X-ray diffraction (XRD). The C-V and other characteristics the devices showed good hysteresis loops with memory window as large as 4V under ±5V sweeping.

A Novel Cell and Array Architecture for FET-Type Ferroelectric Nonvolatile Memories

Wu-quan Zhang，Tian-ling Ren， Chun-xiao Li,et al.

Integrated Ferroelectrics，v40，n1-5，2001，p1413-1420

2 A novel cell using a depletion type Metal-Ferroelectric-Semiconductor FET (MFSFET) as storage device is proposed. Its operations are based on a Metal/Ferroelectric/N-Si/P-Si (MFNP) structure. Read and write disturbance can be avoided in an array of such cells. The basic operations of device have been simulated.

Iterative online training of fuzzy min-max classifier

CHEN Xi, JIN Dongming, LI Zhijian

iconip’02-seal’02-fskd’02[c],singapore,2002-11-18~22:

2 An iterative online training algorithm for the Fuzzy Min-Max Classifier (FMMC) is proposed. The FMMC model is a powerful tool for pattern classification problems, which use the hyper-box representation. Online training of this kind of model has several unwilling properties. Among them a serious one is how to decide the crucial training parameters. This paper proposes an iterative training algorithm to alleviate the difficulty, without losing the online training convenience. Experiments are made following some recent evaluation criteria known in literature, and show that compared with existing method, the new algorithm get better classification performance, better adaptive learning ability, consume less computation resource.

FUZZY PETRI NETS FOR RULE-BASED PATTERN CLASSIFICATION

Xi CHEN, Dongming JIN, Zhijian LI

Proc ICCCAS 2002[C],Chengdu ,China,2002-6-29~7-1:1218-1222.

2 This paper proposes a new model of fuzzy Petri net for rule-based pattern classification and an algorithm to generate the network automatically. The proposed method is modified from fuzzy Min-Max neural network [1]. The modified model is modeled by the fuzzy Petri net formalism, and can be used for pattern classification. The layered model can be viewed as a collection of fuzzy production rules. This convenience makes the classification procedure transparent appose to a black box as most neural network models. Both machine and human can interpret the proposed formal model for pattern classification problem. As an example of the application of the fuzzy Petri net, it is used to classify the Iris Data Set. The result is compared with the reported model.

Using Learning Samples to Construct Fuzzy Logic Systems with the Application to Inverted Pendulum Control

Zhi-Hao Xu, Dong-Ming Jin, Zhi-Jian Li

Proc.ICMLC2002[C], Beijing,China, ,2002-11-4~5:1085-1088

2 Fuzzy Logic Systems (FLS) are nonlinear systems and have very strong function approximation ability. As to achieve FLS ’s function approximation ability, it is very important to find algorithms to synthesis fuzzy rule parameters’ value. Table-Lookup algorithm is a kind of fuzzy rule design method and its computational cost is quite low. Based on the classic Table-Lookup algorithm’s idea, we designed another simpler Table-Lookup synthesis method, and we called it the Simplified Table-Lookup algorithm, and its computational cost is less than the original one. Then we use this algorithm to design the rule parameters of a standard fuzzy controller, which has four inputs and one output. Finally, we use this controller in the inverted pendulum control applications. The results show that our simplified algorithm can realize a stabilization controller.

An analytical Model for High Performance Capacitive RF MEMS Switch Design

Ze-wen Liu, Xiao-feng Lei, Yun Xuan, Zhi-jian Li, Li-tian Liu

Internation Joural of Nonlinear Science and Numerical Simulation, Vol. 3, No.3-4, 365-368, 2002.

2 In this paper we present a precise analytical model for high performance capacitive RF MEMS switch design. Based on this model, the parameters that can influence the switch performance are discussed. The most important geometric parameters are membrane length and thickness, the distance between membrane and lower electrode, the lower electrode length, and the membrane material stress. A capacitive RF switch with optimized structure and expected to actuated with low operation voltage was proposed. The membrane and the lower electrode length are 400mm and 180mm respectively. Aluminum is used as metallic structure materials. Measurement result shows the switch can be actuated with a voltage of 12.3V.

FABRICATION OF A NOVEL Capacitive RF-MEMS Switch

Lei Xiaofeng, Liu Zewen, Xuan Yun, Liu Litian, Li Zhijian, Liu Jianshe

Pacific Rim Workshop on Transducers and Micro/Nano Technologies, Xiamen University, China, July 23, 2002

2 A simple technology to fabricate metal membrane MEMS switch for RF circuit is presented. All the process steps are achieved by surface micromachining techniques. Among these, positive photoresist (PR) is used as sacrificial layer. During this process, pure nitric acid is used to remove the PR layer through small etching holes. The experiments results indicate that there is little influence on the structure of the device under certain experimental conditions. For the sake of improving the switch’s insertion loss and isolation loss, a ferrorelectric film replaces the SixNy usually used. By use of ferrorelectric film the switch has very high on-off capacitance ratios in the range of 600~1000, much higher than which of SixNy. In our experiments Ba0.5Sr0.5TiO3(BST) film, which is prepared via Sol-Gel and wet-etching patterning, serves as the dielectric layer. A fixed-fixed beam capacitive switch is realized using this technology.

Stacking faults and their effects on ferroelectric properties in strontium bismuth tantalite

Y. Ding, J.S. Liu, J.S. Zhu and Y.N. Wang

J. Appl. Phys. 91(4), 2255-2261 (2002).

2 The stacking faults and their effects on ferroelectric properties in strontium–bismuth–tantalite SrBi2Ta2O9 have been studied by transmission electron microscopy (TEM) and ferroelectric hysteresis loop measurement. The structure of SrBi2Ta2O9 consists of Bi2O2 layers and double perovskite type TaO6 octahedral units. There are four possible types of nonstiochiometric stacking faults: two intrinsic faults by removing either one or two perovskite layers and two extrinsic faults by inserting either one or two perovskite layers. TEM investigation reveals that the stacking faults are the extrinsic type. The extrinsic stacking faults in high density might destroy the ferroelectricity, and the reasons are discussed. With excess Bi, the density can be held low efficiently, and with deficient Sr the stacking faults change its form.

Study on the micromachining of porous silicon formed selectively in low-doped substrate

Zhou Jun, Wang Xiaohong, Xie Kewen, Dong Liang, Liu Litian

Pacific rim workshop on transducers and micro/nano technologies July 22~24, 2002,Xiamen,China

2 Porous silicon (PS) is emerging in micromachining technology as an excellent material for using as a sacrificial layer. In this paper, PS is formed in locally doped areas on the Si Substrate by ion implanting selectively. The degree of its laterally formation under microstructure is studied in various conditions and a freestanding microstructure has been demonstrated.

Characteristics of Silicon-Based BaxSr1-xTiO3 Thin Films Prepared by a Sol-Gel Method

Ren TL, Wang XN, Liu JS, Zhao HJ, Shao TQ, Liu LT, Li ZJ

J.Phys.D: Appl.Phys., 35(9):923- 926, 2002.

2 Silicon-based BaxSr1-xTiO3 (BST) thin films have been prepared by a sol-gel method with rapid thermal annealing (RTA) processes. Phase structure of the films has been investigated by x-ray diffraction. Atomic force microscopy studies reveal a dense and smooth surface of the sol-gel prepared films. Microstructure and electrical properties of the BST films can be affected by the substrate and the annealing process. RTA method is found to be very efficient to improve the electrical properties of the films. Dielectric constant and dielectric loss of the BST films at 100 kHz are 230 and 0.02, respectively. Leakage current density of the BST capacitors is 1.6 x 10(-7) A cm(-2) at 3V.

A New Sol-gel Prepared Silicon-based Ferroelectric Sandwich Structure

Ren TL, Zhang LT, Liu LT, Li ZJ

Journal of Sol-gel Science and Technology, 24(3): 271-174, 2002

2 A novel silicon-based PbTiO3/Pb(Zr,Ti)O-3/PbTiO3 (PT/PZT/PT) sandwich structure has been prepared using a sol-gel method. The annealing temperature is greatly reduced compared with those structures without PT layers. Capacitance-voltage (C-V), leakage current-voltage (I-V), polarization-field (P-E), dielectric-frequency response and polarization fatigue of the sandwich structure are examined. The relative dielectric constant, the coercive field and the remanent polarization of the PZT films are measured to be about 900, 18 kV/cm and 16 muC/cm(2) respectively. The current density is less than 5 x 10(-9) A/cm(2) below 200 kV/cm. The dielectric constant of the structure remains constant at low frequency, and decreases to some degree at high frequency. The retained polarization does not change significantly after 8 x 10(9) read/write cycles. The PZT films are proved to have very good dielectric and ferroelectric properties. The new PT/PZT/PT sandwich structure can be valuable for memory devices and other applications.

Design Optimization of Beam-Like Ferroelectrics-Silicon Microphone and Microspeaker

Ren TL, Zhang LT, Liu LT, Li ZJ

IEEE Transactions on Ultrasonic, Ferroelectrics and Frequency Control, 49(2): 266-270, 2002

2 Design optimization of beam-like ferroelectrics-silicon integrated microphone and microspeaker is studied. The Pt/Pb(Zr,Ti)O-3/Pt/SiO2/Si3N4 cantilever structure is designed theoretically using multimorph model. The sensitivity and the sound pressure level (SPL) of the integrated microphone and microspeaker are calculated. It is found that the sensitivity of the microphone and the SPL of the microspeaker are very high. This integrated microphone and microspeaker will be valuable for high quality micro-acoustic devices.

A Silicon-Based Ferroelectric Capacitor for Memory Devices

Ren TL, Zhang LT, Liu LT, Li ZJ

Chinese Physics Letters, 19 (3): 432-433, 2002

2 We study a silicon-based PbTiO3/Pb(Zr-0.53 Ti-0.47)O-3/PbTiO3 capacitor, prepared by an improved sol-gel method. The ferroelectric capacitor has a high remanent polarization of 15 muC/cm(2) at a coercive field of about 30 kV/cm, an ultra-low leakage current density of 0.1 nA/cm(2), and almost fatigue free properties. It can be used as a promising candidate for ferroelectric memory devices.

Characterization of Mn-Doped Ba1-xSrxTiO3 Thin Films Prepared By Sol-Gel Method

Ren TL, Bao JB, Wang XN, Liu JS, Liu LT, Li ZJ, Li XJ

Chinese Physics Letters, 19(11): 1724-1726, 2002

2 Undoped and Mn-doped Ba1-xSrx(BST) thin films have been fabricated on Pt/Ti/SiO2/Si by an aqueous acetate sol-gel method. The BST stock solution can be easily mixed with an aqueous metal ion solution and is stable at room temperature. The annealing temperature of the doped and undoped films is between 650-750degreesC. The x-ray photoelectron spectra results show that the Mn 2p(3/2) valence state in the BST is the same as that of the original Mn(11) dopant. The dielectric constant of the BST thin films can be increased to 800, and the loss tangent can be decreased to 0.01 due to the Mn(II) doping. The leakage current of the BST films can also be greatly reduced.

Fabrication of a Cantilever Structure for Piezoelectric Microphone and Microspeaker

Lin-Tao ZHANG, Tian-Ling REN, Jian-She LIU, Li-Tian LIU and Zhi-Jian LI

Jpn.J.Appl.Phys.,41(11B):7158- 7159, 2002

2 In this paper, a novel piezoelectric microphone based on a lead zirconate titanate [Pb(Zr, Ti)O3, PZT]-coated silicon cantilever is presented. The main structure of the cantilever is composed of the Pt/PZT/Pt/Ti/SiO2/Si3N4/SiO2/Si multilayer structure. An optimum fabrication process of the PZT thin films and the cantilever has been developed. The acoustic outputs of the fabricated microphones have been measured with a standard microphone and a high sensitivity of 40 mV/Pa can be obtained. The frequency response of the microphone is very flat in the audio frequency range.

Microstructure and electrical properties of (Ba,Sr)TiO3 thin films prepared by a sol-gel method

Ren TL, Wang XN, Liu JS, Zhao HJ, Shao TQ, Liu LT, Li ZJ

INTEGRATED FERROELECTRICS, 45: 13-21, 2002

2 Silicon-based BaxSr1-xTiO3 (BST) thin films have been prepared by a Sol-Gel method with rapid thermal annealing (RTA) processes. Phase structure of the films has been investigated by X-ray diffraction (XRD). Atomic force microscopy (AFM) studies reveal a smooth, dense and crack-free surface of the BST films. Microstructure and electrical properties of the BST films can be affected by the substrate and the annealing process. RTA method is found to be very efficient to improve the electrical properties of the films. Dielectric constant and dielectric loss of the BST films at 100 KHz are 230 and 0.02, respectively. Leakage current density of the BST capacitors is 1.6×10-7 A/cm2 at 3V.

XPS characterization on the Mn-doped BST thin films prepared by sol-gel method

Bao JB, Ren TL, Liu JS, Wang XN, Liu LT, Li ZJ, Li XJ

INTEGRATED FERROELECTRICS, 45: 31-38, 2002

2 Undoped and Mn(II)-doped barium strontium titanate (BST) thin films have been prepared by a "water based" sol-gel method. With this method, BST stock solution can be easily doped with any concentration of aqueous metal ion solution and can be stocked for 3similar to4 days at room temperature. The crystallization temperature of 650squaresimilar to750square is suitable for the films from traded-off of both the X-ray diffraction (XRD) patterns and the surface topography. The Mn 2p(3/2) X-ray photoelectron spectra (XPS) pattern is given for the first time in the thin film and shows the valence state of the Mn-doped BST has a same valance with the Mn(II) dopant. Considering the peak shift of the binding energy, it is proposed that the Fermi level of the Mn-doped BST has been shifted down by 0.7 eV.

High quality ferroelectric capacitor for FeRAM applications

Ren TL, Zhang LT, Wang XN, Wei CG, Liu JS, Liu LT, Li ZJ

INTEGRATED FERROELECTRICS, 46: 47-53, 2002

2 Lead zirconate titanate (PZT) based ferroelectric capacitor using lead titanate (PT) as seeding layers has been prepared on silicon wafer by an improved sol-gel method. The novel ferroelectric capacitor has high dielectric constant of about 1200, ultralow leakage current density of 0.1nA/cm(2) , high remanent polarization of 20 muC/cm(2) at coercive field of about 30 kV/cm, and almost fatigue free properties. The capacitor structure can be valuable for FeRAM applications.

Fabrication of (100) orientated PZT thin films for MEMS applications

Zhao HJ, Ren TL, Liu JS, Liu LT, Li ZJ

INTEGRATED FERROELECTRICS, 46: 79-86, 2002

2 High quality silicon-based PZT thin films were prepared using an improved sol-gel process. PT thin film was adopted as the seeding layer. The fabrication technique and the growth mechanism of the PZT thin films crystallized with (100) preferred orientation were studied through changing the pre-annealing temperatures, the annealing temperatures and the thickness of the PT seeding layer. It was shown that the PZT thin films with the suitable seeding layer had a more highly (100) preferred orientation. The dielectric response and dielectric loss of the PZT thin films were also measured. In the radio-frequency (RF) region, the dielectric constant was about 150 and the dielectric loss was less than 0.01, respectively.

A novel single-FET cell and array architecture for ferroelectric nonvolatile memories

Zhang WQ, Ren TL, Li CX, Liu LT, Zhu J, Li ZJ

INTEGRATED FERROELECTRICS, 48: 101-107, 2002

2 A novel Metal-Ferroelectric-Semiconductor FET (MFSFET) device with special doped source/drain is proposed. The special shaped drain and source regions will form a JFET (Junction FET) deep in the bulk. Write disturbance can be avoided in an array of such cells.

Preparation and etching of silicon-based piezoelectric thin films for integrated devices

Zhao HJ, Ren TL, Zhang LT, Liu JS, Liu LT, Li ZJ

INTEGRATED FERROELECTRICS, 48: 271-279, 2002

2 Lead-zirconate-titanate (PZT) and ZnO thin films on silicon substrates were prepared by a sol-gel method. Phase characterization and crystal orientation of the films were investigated by X-ray diffraction analysis (XRD). It was shown that the PZT thin films had a perfect perovskite structure after annealed at a low temperature of 600square, and the ZnO thin films were well crystallized with (002) preferred orientation at a low annealing temperature of 400square. PZT thin films were chemically etched using HCl/HF solution through typical semiconductor lithographic process, and ZnO thin films were wet etched using acidic and alkaline etchants. The etching conditions were optimized. The etching precision can be higher than 1 mum .

A novel miniature optical switch array with cantilever micromirrors driven by PZT films

Ren TL, Xu Y, Liu LT, Li ZJ

INTEGRATED FERROELECTRICS, 49: 193-202, 2002

2 A novel miniature optical switch array integrated with cantilever micromirrors driven by PZT (Lead Zirconium Titanate) films has been proposed. The micromirrors with uniform surfaces are fabricated in several mask steps by anisotropic bulk etching of (110) silicon wafer using KOH solutions with ultrasonic agitation. After the PZT films have been prepared, the wafer is etched from the upper side using Induced Couple Plasma etching (ICP) to form the whole cantilever structure. Each cantilever micromirror is driven by PZT films and is implemented to cut off the laser beam or let it pass through, enabling the switching. The optical switch array composed of the silicon micromirrors can be integrated to form a monolithic 4x4 optical crossconnect (OXC) with dimensions of about 6x6mm(2) , and is scalable to large array.

RF-MEMS BAW filter using surface micromachining

Cong P, Ren TL, Liu JS, Liu LT

INTEGRATED FERROELECTRICS, 50: 71-79, 2002

2 RF-MEMS bulk acoustic wave (BAW) filter using surface micromachining is successfully achieved using PZT as the piezoelectric layer. The resonant frequency is adjusted by changing the thickness of the SiO2 film on the top of the upper electrode. By etching the sacrificial porous silicon (PS) layer, the suspended structure is formed. This structure is able to eliminate the influence of the thick support film to the filter, and to improve the IC process compatibility and quality of the filter. Each resonator forms a self-supporting structure, so that the cross-talk between resonators with different frequencies will be dramatically reduced. In addition, dry-etching processes are used to improve the quality of the device. It is found that reactive ion etching (RIE) can be used to etch PZT/PT and platinum with a rate of 200 and 100 Angstrom/min respectively using HCFC-124 as the etching gas.

Modeling and simulation of thin-film bulk acoustic resonators

Zhao HJ, Ren TL, Liu JS, Liu LT, Li ZJ

INTEGRATED FERROELECTRICS, 50: 81-89, 2002

2 The PZT-based thin film bulk acoustic resonator (FBAR) structure had been simulated and optimized. The results revealed that the resonant frequency of the FBAR can be controlled by adjusting the mono-layer thickness of the sandwich structure. Dependence of resonant frequency upon the thickness of the piezoelectric film was obtained. The relation of the buffer layer thickness and the quality factor (Q value) had been investigated. The structure of a ladder-type FBAR filter with the center frequency of 2 GHz and the 3-dB bandwidth of 100MHz had been designed. The CPW for the FBAR with characteristic impedance of 50 Omega was optimized.

Near- Infrared Si0.7Ge0.3 / Si p- i- n Photodetector Fabricated on SOI in CMOS Technology

Guo Hui ,Guo Weilian ,Zheng Yunguang ,Li Chen ,Chen Peiyi

CHINESE JOURNAL OF SEMICONDUCTORs 23,(1) p16~20 (2002)

2 We report a novel lateral Si0.7Ge0.3 p-i-n high-speed photodetector fabricated on SOI substrate using a UHV/CVD SiGe/Si process and a standard CMOS technology.The photodetector attains a responsivity of 0.38 A/W at its peak response wavelength λ=930nm.Biased at 3 V,the photodetector exhibits low dark current less than 1 nA, small parasitic capacitance of 0.8 pF and short rise-time of 2.5 nS.The overall performance and process compatibility with CMOS technology of the device make it applicable to monolithic silicon-based photoreceiver operating at wavelength larger than 900nm in high-speed optic data links ,photocoupling ,and photodetecting.

Novel strained Si/relaxed SiGe channel PMOSFETs

Li chen, Luo guangli, Chen Peiyi

Thin Solid Films, Vol. 409 (1) (2002) pp. 112-115.

2 Due to the high hole mobility both in the surface strained Si and buried relaxed SiGe channels, we successfully fabricated a novel strained Si/relaxed SiGe channel PMOSFET on the heterostructure strained Si/relaxed SiGe/strained Si/relaxed SiGe buffer layer/grading SiGe layer, grown by home-made UHV/CVD system, which is commonly used in the ‘buried’SiGe NMOSFET. This device is easier to integrate with SiGe NMOSFET to form SiGe CMOS, than strained SiGe channel PMOSFET. Then the process is presented.With Vgs =3.5 V, the maximum saturated transconductance is found to be twice as large as that of the control Si PMOS, and approximates to that of a traditional strained SiGe channel PMOS.

Strained Si-Channel Heterojunction n-MOSFET

Shi Jin, Huang Wento and Chen Peiyi

CHINESE JOURNAL OF SEMICONDUCTORs 23,(7) p683~689 (2002)

2 The advances in the growth of pseudomorphic silicon-germanium epitaxial layers combined with the strong need for high-speed devices have led to increased interest in silicon-based heterojunction field-effect transistors. Here we present a kind of strained Si-channel n-MOSFET, which can offer a better performance comparing to the Si device. When applying to the sample with W/L value of 14/7, a 48.5% improvement can be achieved in electron mobility.

Vertical Ordering Stacked Ge Quantum Dots Grown by HV/CVD

Huang Wentao, Luo Guangli, Deng Ning, Chen Peiyi, Tsien Pei-Hin,

International conference on Microelectronics and Nano technology，2002.9.26~27，p122

2 The size distribution of Ge quantum dots and strain in Si spacers of vertically stacked Ge quantum dot arrays prepared by high vacuum chemical vapor deposition (HV/CVD) system were studied. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) have been combined to investigate impact of the growth parameters on the vertical ordering of the Ge quantum dots with a 50 nm Si spacer layer. It’s shown that the growth temperature 550 oC and the growth time 15s in our system are suitable for the growth of small size, high-density Ge quantum dots. Ordering of a five-stacked-layer Ge quantum dots is obviously seen, with a concomitant shape change to uniform quantum dots.

A Novel Package for Microelectronics: Wafer Level Package(WLP)

Jia Songliang, Hu Tao

Global Electronic Components, 2002. No. 2, 7～10

2 A novel package for Microelectronics—Wafer Level Package(WLP), which is making rapid progress now, will be presented in this paper. The main characteristics of WLP is: the wafer is singulated into a single device just after the most packaging process is finished on the whole wafer, which is different from the traditional packaging. In this paper, the definition and main advantages/disadvantages of WLP, as well as the main process, such as pad redistribution and bumping, will be discussed in detail.

Effect and control of moisture content in electronic package

Jia Songliang

Electronics & Package , 2002,Dec.,Vol.2, No.6, p12~16

2 The effect of moisture content in electronic component hermetic package on reliability of components has been introduced in this paper 。Three main sources of moisture in package and the process control method are presented。

Tolerance Design in the Electronic Devices Fabrication

Jia Songliang ，Wang Shuidi

The Proceeding of the 11th National Annual Conference of Reliability Society，p.257~260, Yinchuan,Ningxia, Sep.2002

2 This paper introduce the tolerance design for electronic devices fabrication,including the tolerance design of safety working current in silicon-aluminum wire at package ,the tolerance design of resistance value in IC and the tolerance design of stress ，which the glass can be stood against in metal-glass hermetic package.

FABRICATION OF A NOVEL Capacitive RF-MEMS Switch

Lei Xiaofeng, Liu Zewen, Xuan Yun, Liu Litian, Li Zhijian, Liu Jianshe

Pacific Rim Workshop on Transducers and Micro/nano Technologies, p789-792， July 22-24, 2002 Xiamen, China

Design and Simulation of a Wide Tuning Range MEMS Tunable Capacitor For RF Applications

Liang Xuedong, Liu Zewen,Liu Litian,Li Zhijian,

IEEE HDP’02,June 30-July 3, shanghai, China

2 We present a novel MEMS tunable capacitor with a wide tuning range. Different from the conventional parallel-plate capacitors, this capacitor consists of three pairs of plates. One pair of them are used as capacitor plates, and the other two are used as controlling plates. AC signal passes through the capacitor plates while DC controlling voltage is applied between the controlling plates. By simulation with Ansys software, we get the tuning range is up to 214%, largely beyond the theoretical tuning range limit (50%) of conventional two-parallel-plate capacitors. It can be easily integrated in RF circuits for this simple process of fabrication.

Porous Silicon and Its Application in RF-MEMS

Ding Yong, Liu Zewen, Liu Litian, Li Zhijian

International conference on Microelectronics & Nanotechnology, Nov. 2002, Beijing.

2 Suspended RF-MEMS device realized using Porous silicon as sacrificial layer is presented. The process is simple and CMOS compatible. The porous silicon is released with TMAH solvent. The robust suspended SiO2 thin film is obtained and the RF-MEMS devices are fabricated on it.

Design and Simulation of a High-Tuning-Range RF MEMS Voltage-Controlled Capacitor

Liang Xuedong, Liu Zewen, Liu Litian, Li Zhijian

CIE 2th national conference on nantechnology and Its application, Nov. 27-29, Ningbo, China

2 Based on the analysis to the traditional parallel-plate capacitor, we present a novel MEMS tunable capacitor with a wide tuning range. Different from the conventional parallel-plate capacitors, this capacitor consists of three pairs of plates. One pair of them are used as capacitor plates, and the other two are used as controlling plates. AC signal passes through the capacitor plates while DC controlling voltage is applied between the controlling plates. By simulation with Ansys software, we get the tuning range is up to 214%, largely beyond the theoretical tuning range limit (50%) of conventional two-parallel-plate capacitors. It can be easily integrated in RF circuits for this simple process of fabrication.

Study on Substrate Effects of Micromachined Planar Inductor

Liu Zewen, Dong Ying, Ding Yong

CIE 2th national Conference on Nanotechnology and Its Application, Nov. 27-29, Ningbo, China

2 This paper presents a calculation method for the Q value of planar inductor. The effects that determine the merit of planar spiral inductor are analyzed. Based on an electrical model of the microamchined inductor, eddy current effect induced parasitic resistance and the capacitance due to the lossy substrate are carefully studied. The obtained theoretical result shows the Q value is related to both the inductor geometric size and the work frequency. An optimized planar inductor can be realized through the theoretical analysis and calculation

Design, simulation and optimization of a highly sensitive micromachined membrane

Chen Jing, Liu Litian, Li Zhijian

Research and progress of solid state electronics,v22,n1, Feb. 2002

2 A highly sensitive membrane is essential for many devices based on Microelectromechanical System (MEMS). For micromachined membrane, there is significant internal (residual) stress, which strongly decreases the mechanical sensitivity of membrane. The application of corrugated membrane offers the possibility to increase the sensitivity of membrane without changing process conditions, thus eliminating the effect of initial stress. A simple analytical model predicts that the improvement of sensitivity depends critically on the geometric parameter of the corrugated membrane. A simple and efficient process to fabricate the corrugated membrane has been presented, several corrugated profiles are proposed with this process. To get the optimal value of the design parameters, Finite Element Method (FEA) has been used. The optimized corrugated membrane show a sensitivity more than one order larger than that of the flat membrane of equal size and thickness. Many high performance MEMS devices can be realized with this technique.

A Review of Silicon Micromachined Microphone

Chen Jing, Liu Litian, Li Zhijian

China Integrated Circuit, v35, Apr.2002

2 Silicon micromachined microphone(SMM) based on MEMS technology is leading another revolution of modern acoustic devices. In this paper, the state-of-the-art of silicon micromachined microphone is reviewed. In addition, the operation principle of the most prevailing condenser miniature microphone is briefly analyzed. Researchers of IMETU (Institute of Microelectronics, Tsinghua University) have achieved fruitful results in SMM. A novel corrugated structure has been proposed to improve the sensitivity of SMM. Furthermore, the fabrication process is compatible with the standard IC process. The performance of this SMM is among the best in the present reports.

Design of uPEMFC Fabricated With Porous Silicon

WANG Xiao-hong, XIE Ke-wen, ZHOU Jun, LIU Li-tian

CIE 2th national Conference on Nanotechnology and Its Application, Nov. 27-29, Ningbo, China

2 Abstract: A novel material porous silicon is used as diffusion layer in uPEMFC (Micro Proton Exchange Membrane Fuel Cells) for its loose and porous structure and compatibility with IC process. Study of the formation of porous silicon and metal sputter deposition on the porous silicon is performed. A fabrication process of mPEMFC based on the technology of MEMS and film deposition is presented.

Study of RF-=MEMS BAW Filter Using Surface Micromachining

CONG Peng LIU Yanxiang REN Tianling LIU Litian

PIEZOELECTRICS&ACOUSTOOPTICS Vo1.24 No.1 Fed.2002

2 The analytical solutions of the wave equation for the electrode-piezoelectrics-electrode sandwich structure on support film in the BAW RF resonators are presented. The advantages and disadvantages of fabrication BAW RF filter using surface and bulk micromachining are discussed. A novel structure of front end passband bulk acoustic wave (BAW) filter using surface micromachining is given.

Design and Fabrication of Vertical Cavity Surface Light Emitter

Dan Yaping Yue Ruifeng Wang Yan Liu Litian

Chinese Journal of Scientific Instrument (accept)

2 This paper designs a novel Vertical Cavity Surface Light Emitter (VCSLE) and simulates the reflectance of its Bragg reflective mirror as well as the effect of film thickness errors on the reflectance. The result proves PECVD meets the technical requirements of the preparation of VCSLE and a device with excellent performance is fabricated.

A study of the annealing Effects on oxygen-rich silicon oxynitride

DAN Ya-ping; YUE Rui-feng; WANG Yan; YAO Yong-zhao; XU Yang; LIU Li-tian

Chinese Journal of Semiconductors,2002,No.23:388-393

2 A detailed study is carried out on four oxygen-rich silicon oxynitride samples as an as-deposited one and other three ones annealed at 600℃, 750℃ and 900℃ respectively by Infrared spectroscopy and x-photoelectron spectroscopy. In addition to the release of N and H, we observe for the first time the dissociation of Oxygen. The release of N, H and O and the microstructure are different after different temperature annealing. And we propose five chemical procedures to interpret these observations.

Design and Fabrication of Silicon Micromachining Suspended Inductor

Ding Yong Liu Zewen Liu Litian Li Zhijian

Acta Electronica Sinica

2 The factors which determine the quality (Q) factor of planar spiral inductor were presented in this paper, and a technology to fabricate suspended MEMS devices for RF circuits is presented. A simplified electrical model is used to study the influence of high-frequency magnetic fields on the parasitical resistance, including the eddy effect and skin effect. To get high-Q suspended inductor, porous silicon (PS) is used as sacrificial layer, and SiO2 film is used as a support membrane. During the process, TMAH solution with Si powder and (NH4)2S2O8 is used to remove the PS layer through small etching holes with no influence on the uncovered Al in the devices. A suspended inductor structure is realized using this technology. The fabrication is proved to be reliable.

OPTICAL AND THERMAL DESIGN FOR MICROBOLOETER

Dong Liang，Yue Rui-Feng，Liu Li-Tian

Journal of Infrared and Millimeter Waves (accept)

2 This paper describes the optical and thermal design of microbolometer with four-leg microbrige. The optical characteristic of multilayer structure consisting of SiO2 infrared absorber film / poly-Si thermosensitive film / SiO2 support film is analyzed, and the influence of thickness of the infrared absorber film on average absorptance of the multilayer structure is investigated. During thermal design, the average infrared absorptance of microbolometer is not fixed as a constant but changed with thickness of absorber film, which is different from the conventional method. The optimized thickness of infrared absorber film and length of support leg are achieved through Finite Element Analysis software ANSYS5.7.

Influence of Thermal Environment on Electrical Properties of Micromachined Polysilicon Thin Film Resistor

DONG Liang YUE Ruifeng LIU Litian XU Yang LI Zhijian

Research and progress of solid state electronics (accept)

2 Micromachined polysilicon thin film resistors supported by microbridge and by thin film have been designed and fabricated by CMOS process and micromachining technology. After measuring the temperature coefficient of resistance (TCR) and I-V characteristics, the influence of thermal environment, such as the degree of thermal insulation and the pressure of atmosphere, on electrical properties of these resistors are investigated and discussed.

Development of linear uncooled microbolometer array made of poly-SiGe film

DONG Liang YUE Ruifeng LIU Litian

Research and progress of solid state electronics (accept)

2 Poly-Si0.7Ge0.3 film is prepared by ultra high vacuum chemical vapor deposition (UHVCVD) system. The dependences of the poly-Si0.7Ge0.3 resistance on operation temperature and on annealing temperature are investigated. Optimized structure of two-leg supported microbridge for microbolometer is designed, with a surface area of 80μm×80μm, a leg length of 220μm and a leg width of 8μm. With bulk silicon micromachining technique, a 8×1 linear microbolometer array based on poly-Si0.7Ge0.3 resistor as thermosensitive element is fabricated. The characteristics of the linear array are investigated to infrared radiation in the spectral region of 8~14μm, with a black body temperature of 773K. Measurements show that for pixels of the linear array, a responsivity of 6.23kV/W～6.40kV/W, a detectivity of 2.24×108cmHz1/2W-1～2.33×108cmHz1/2W-1 and a thermal response time of 21.2ms～22.2ms are achieved at a chopper frequency of 30Hz.

Preparation of Poly-Si0.7Ge0.3 Film

Dong Liang Yue Ruifeng Huang Wentao Liu Litian

Chinese Journal of Scientific Instrument,vol.23 No.3 2002

2 Poly-Si1-xGex film is prepared by ultra high vacuum chemical vapor deposition (UHVCVD), and Ge mole fraction is calculated based on Raman spectra. Temperature dependence of the poly-Si0.7Ge0.3 film on resistance is described, which reveals -2.10%/oC of TCR can be achieved.

Design and Fabrication of Linear Uncooled Microbolometer Array

Dong Liang Yue Ruifeng Liu Litian

Chinese Journal of Scientific Instrument, vol.23 No.3 2002

2 In this paper, optimized structure of microbridge for microbolometer is designed. Using micromaching technique, a 8×1 linear microbolometer array using poly-Si0.7Ge0.3 resistor as thermosensitive element is fabricated. The whole processing temperature is limited below 650oC.The microbridge with surface area 100μm×100μm is supported by two legs with the length of 220μm and the width of 8μm

Uncooled Infrared Detector based on a-Si:H Thin Film Transistor

Dong Liang Yue Ruifeng Liu Litian

Chinese Journal of Scientific Instrument, vol.23 No.3 2002

2 In this paper, a novel uncooled infrared detector (TFT-IRDT) based on temperature dependence of the channel current in amorphous silicon thin film transistor (a-Si:H TFT) is proposed. It utilizes a-Si:H TFT as thermosensitive element of infrared detector. The readout circuit is configured with differential amplifier whose input pair is two TFTs. It is revealed by PSPICE simulator that the output signal is linearly with temperature increment, and the temperature sensitivity calculated is about 4.1mV/K at room temperature.

A novel micromachined uncooled infrared detector based on temperature dependence of drain current of MOSFET

Dong Liang, Yue Ruifeng, Liu Litian, Li Zhijian

Infrared and Laser Engineering, vol.31,No.6 2002

2 A novel micromachined uncooled infrared（IR）detector based on temperature dependence of drain current of MOSFET is proposed for the first time. It utilizes a MOSFET fabricated on SOI substrate as thermosensitive element. An IR resonance cavity formed on passivation layer of MOSFET improves the IR(8~14μm) absorptivity and a microbridge fabricated using micromachining technique provides a low thermal conductance. The temperature dependence of drain current of MOSFET, IR detection principle and device structure are presented. The performance of the IR detector based on numerical analysis and FEA (finite element anlysis) is estimated that the detecivity (D*) can reaches 109～1010cmHz1/2W-1.

Study on Using Porous Silicon as Sacrificial Layer in High Resistivity Silicon

Dong Liang Yue Ruifeng Liu Litian

Chinese Journal of Scientific Instrument, vol.23 No.3 2002

2 In this paper, porous silicon is formed in locally defined areas on the Si substrate with high resistivity. To fabricated freestanding microstructure, the surface micromaching technique using porous silicon as sacrificial layer which is formed when microstructure has been processed is studied.

An Improved Macro Model of Ferroelectric Capacitor for FeRAM Design

Tian-Ling Ren, Wu-Quan Zhang, Chun-Xiao Li, et al.

Acta Electronica Sinica. v29, n8, 2001, p1135-1137

2 An improved macro model is proposed based on ZSTT model, which is derived from the hysteresis loop of a ferroelectric capacitor. This model is proved to be very successful in the optimization and simulation for FeRAM design. It can also be adapted to express the P-V characteristic of a ferroelectric capacitor imposed by nonsymmetrical voltage，which is useful in some new operation scheme.

A Study on a Synapse of Neural Networks Based on Dynamic Storage and Analog Calculation

ZHOU Wei-xiong JIN Dong-ming

Microelectronics, 2002,32(2): 131-135.

2 A Synapse of Analog Neural Networks Based on Dynamic storage and Analog Calculation is presented. The storage time of Dynamic storage cell can reach 102ms. The circuit of the analog calculation cell is simple, it has high accuracy and high working speed. Those synapses which are constructed by the dynamic storage cell and analog calculation cell can meet the requirement of the realization of large scale neural networks. The results of HSPICE simulation are in good agreement with the theoretical analysis.

Research on Genetic Algorithms-based Fuzzy Control

Jiang Hai-lin, Jin Dong-ming

Acta Electronica Sinica, 2002,30(5):676-679.

2 This paper proposes a design of the self-adaptive learning fuzzy controller based on Genetic Algorithms optimization. Researching how this theory optimizes the parameters of fuzzy control in the whole scope is taken. To be considered with the implementation of hardware, the discussion is focused on the generation of control rules and the dynamic learning of the rules store. Some new computational methods are used based on traditional genetic algorithms. The nonlinear control system of inverted pendulum is simulated on-line with this design, simulated by simulate tools- Simulink in Matlab, which proves the validity and the applicability of this proposed control method. This approach also provides a valuable theory basis to the implement of hardware chip.

A New Kind of Fuzzy Neural Network Classifier

CHEN Xi, JIN Dong-ming, LI Zhi-jian

Acta Electronica Sinica, 2002,30(6): 928-933

2 A Multi-Resolution Combined Classifier (MRCC) model and its learning algorithm are proposed. The MRCC is a modification of Simpson’s original Fuzzy Min-Max (FMM) Neural Network Classifier. It overcomes some undesired properties of the original model: specifically, training results do not depend heavily on pattern presentation order and hyper-box expansion is not limited by a fixed maximum size. Compared with the original model, a new parameter called the reliability of hyper-box is introduced in MRCC, which presents the correct classification rate of a single hyper-box. A locally uniform distribution hypothesis is also introduced, so that the reliability of hyper-box parameter can be adjusted on-line. In addition, the multi-resolution combination method alleviates the effort to select a optimal parameter for the maximum size of a hyper-box in the original algorithm. Experiments were made following some recent evaluation criteria known in literature, and show that compared with original model, the MRCC model has better classification performance, more adaptive learning ability and creates less hyper-boxes.

A Review of the Research on Realization of Analog Neural Cells

ZHOU Weixiong JIN Dongming LI Zhijian

Research and progress of solid state electronics, 2002,22(3):268-279.

2 Artificial neural network is an important method in the field of modern information processing. Comparing to software realization method, hardware realization method can fully exert the characteristics of parallel work of neural network. Neural networks realized by analog circuits have simpler structure, lower power consumption and higher speed and occupy small chip area than by digital circuits. There can be place more analog neural cell on a chip. Neural cells are fit to be realized by analog circuits. Focus on the most widely used linear-synapse neural cells and quadratic neural cells; this paper is specified in three facets: weight-storage circuits, synapses circuits, the circuits of neuron. Various kinds of realization methods are reviewed in comparison of their characteristics. At the same time, kernel issues that should be considered in the realization of neural networks are put forward. And finally a perspective for the development of realization of neural networks is dressed out in the paper.

A Method for Rule Extraction Based on Hyper-Box Representation

CHEN Xi, JIN Dong-ming, LI Zhi-jian

Acta Electronica Sinica,2002,30(9):1379-1383.

2 In this paper, we discuss a new method for rule extraction based on hyper-box representation. The method is deducted from the MRCC model, used for pattern classification. The method partitions the pattern space with multi-dimensional fuzzy hyper-boxes, and assigns a class label with certainty degree for each variable fuzzy region. These rules are extracted from numerical data through a recursive learning procedure. Experiment shows the efficiency of rule extraction procedure.

A Modified Sol-gel Coating Method for BST Thick Films on Silicon Substrates

Wang Zheyao, Liu Jianshe, Ren Tianling, Liu Litian and Li Zhijian

Chinese Journal of Semiconductors. 23(8), 830-834 (2002)

2 A modified dip-spin method for BST thick films preparation is introduced. In order to avoid crack formation, an organic macromolecule vinyle pyrrolidone (PVP), which has the hybrid effect, is dispersed uniformly into a sol-gel solution containing Ba(CH3COO)2-Sr(CH3COO)2-Ti(OC3H7)4. The thick films are coated by repetitive spin coatings and then annealed at a proper temperature. The maximum thickness can reach up 1 μm by this modified dip-spin method. The dependence of the thickness on the PVP quantity and Mole density are discussed, and some experimental details as well as the SEM photos of the thick films are given.

Investigation of selectively forming porous silicon used in MEMS

XIE Ke-wen, WANG Xiao-hong, CHEN Jing, LIU Li-tian

Chinese Journal of Semiconductors. 23(6),688(2002)

2 Forming porous silicon selectively which is used as a sacrificial layer on the low-doped silicon substrate by using diffusion process and then fabricating free-standing microstructures are presented. A process run is made and the results of the experiment is discussed in detail. The technology of removal porous silicon using KOH solution is also studied.

Study on The Selective Formation of Porous Silicon As a Sacrificial Layer in Microstructure

Zhou Jun, Wang Xiaohong, Dong Liang, Liu Litian

Microfabrication Technology, 2002, No.2

2 The Porous silicon as a sacrificial layer could be fabricated in locally defined areas on the Si substrate, using the selective formation of porous silicon. Presented a technique of fabricating the microstructure first and then performing anode oxidation to form a sacrificial layer of porous silicon. The well freestanding microstructure has been made by this technique. The well freestanding microstructure has been made by this technique. The favrication conditions and selectivity of formation of the porous silicon and masking layer are studied in detail.

The Technology of Using Porous Silicon As a Sacrificial Layer in MEMS

ZHOU Jun, XIE Kewen, WANG Xiaohong, LIU Litian

Research and progress of solid state electronics (accept)

2 Porous silicon is a material used as a sacrificial layer. It has some important applications in surface micromachining technology. Three different processes based on porous silicon as a sacrificial layer are discussed in detail; Freestanding microstructures are fabricated with the latter two separate techniques, then the deposition of film on the surface of porous silicon and masking layer in the fabrication of porous silicon are analyzed. All these provide solid foundation of fabricating diverse freestanding microstructures.

Kinetic Monte Carlo Simulation of initial nucleation stage of 2D Ge islands

Deng Ning Xiao Hong Chen Peiyi Li Zhijian

2^nd National conference on Nano technology and its Application,Ningbo,Nov.2002

2 Initial nucleation stage of 2D Ge islands during the self-organized growth of Ge islands in Si/Ge mismatch system was studied by Kinetic Monte Carlo (KMC) simulation. The diffusion barrier was corrected by introducing a strain field induced by adsorbed atoms. The influence of stain and substrate temperature on nucleation sites and size was investigated. The nucleation of 2D islands was determined by strain field and the self-organized growth can be controlled by modulating the stain on the surface.

Effect of boron pre-deposition on size distribution of self-assembled Ge islands fabricated by UHV/CVD

Ning Deng, Wentao Huang, Yan Wang, Guangli Luo, Peiyi Chen, Zhijian Li

Micronanoelectronic Technology, 2002, vol.39, No.6, p16～20

2 The effects of pre-deposition of boron with different B2H6 flux on the self-assembled growth of Ge islands on Si(1