This paper describes the results of simulation studies for the design of an integrated collimating waveguide lens pair. The lens pair has application in MOEM based optical switches which rely on the free space propagation of an optical beam over a matrix of micro-mirrors. Consideration is given to the simulated tolerance to various misalignment and processing errors.

In this work, the flip-chip method was used for packaging of the RF-MEMS switch on the quartz substrate with low losses. The 4-inch Pyrex glass was used as a package substrate and it was punched with airblast with 250 micrometers diameter holes. The Cr/Au seed layer was deposited on it and the vias were filled with plating gold. After forming the molds on the holes with thick photoresist, the bumps were plated on holes. The package substrate was bonded with the quartz substrate with the B-stage epoxy. The loss of the overall package structure was tested with a network analyzer and was within -0.05 dB. This structure can be used for wafer level packaging of not only the RF-MEMS devices but also the MEMS devices.

The performance of a wide variety of RFID systems depends critically on: how efficiently energy is coupled to and from an electronically coded label; on how effectively it is used within the label; and sometimes on how effectively it is transformed from one form to another within the label. The paper considers the definition of appropriate coupling factors and quality factors which describe these processes, and their role in regulating system performance in the near and far fields of both linear and non-linear process based technologies. Calculations allowing feasibility estimates of some new process combinations on which some RFID systems may be based are presented.

In this paper, we proposed a new First Partial product Addition (FPA) architecture with new compressor (or parallel counter) to CSA tree built in the process of adding partial product for improving speed in the fast parallel multiplier to improve the speed of calculating partial product by about 20% compared with existing parallel counter using full Adder. The new circuit reduces the CLA bit finding final sum by N/2 using the novel FPA architecture. A 5.14ns of multiplication speed of the 16X16 multiplier is obtained using 0.25um CMOS technology. The architecture of the multiplier is easily opted for pipeline design and demonstrates high speed performance.

We propose a novel testing scheme to select good chip of capacitive fingerprint sensor LSIs. Conventional testing uses actual finger touching. For mass production, accuracy, high speed, and low cost are needed in testing. To check the sensor LSI at the wafer level using an LSI tester, we add a self-testing function to each pixel in the sensor LSI. The pixel-self-check extracts error pixels whose output is abnormally fixed. These pixels degrade the fingerprint image. A fingerprint sensor LSI with the self-testing function was fabricated using the 0.5-micrometers CMOS process/sensor process. It demonstrates that the pixel-self-check extracts error pixels accurately. The proposed testing scheme enables the selection of good chips at the wafer level without finger touching.

Two closed form algebraic models describing electrostatic latch and release of micro cantilever beams are presented. The 1st model is based on beam theory with a fixed moment at the boundary to represent the electrostatic force and it predicts that electrostatic pull-in occurs at a beam tip displacement of 46% the initial actuator gap. The 2nd model uses a rigid beam pinned at the anchor with a spring equivalent to the beam's mechanical restoring force attached to the tip and describes electrostatic pull-in occurring at a beam tip deflection of 44% the initial actuator gap. Pull-in voltage measurements of polysilicon cantilever beam arrays (6mm wide, 2mm thick, 160 mm long) correlate to both the 1st and 2nd presented models with errors of 8.2% ((sigma) equals1.3%), and 4.9% ((sigma) equals1.4%), respectively. The 1st and 2nd models were observed to improve pull-in voltage prediction by at least 10.3% and 13.7% respectively when compared to previously presented models without the use of empirical correction factors.

Resonant mode operation is common in many MicroElectroMechanical (MEM) applications including accelerometers, gyroscopes and filters [Kovacs (1998), Nguyen (1999)]. When electrostatic transduction is used in these applications, concerns about cross talk and fringing field effects due to geometry are major issues. In this paper, an electrostatically coupled system is briefly introduced, modeled and the dynamic response due to small parametric (displacement dependant) electrostatic force is analyzed using perturbation methods. The presence of coupled parametric resonance has a very significant effect on the dynamic response. Experimental verification of the occurrence of this phenomenon is also presented here. The coupled oscillator system can also be used as an in situ test device to understand the electrostatic parameters in a system. The method of modeling and analysis presented here is simple, yet captures the dynamic behavior of a system due to a small force. This method can be generalized and will be a useful tool in any resonant MEM system design.

This study introduces a novel design for low-cost MEMS devices, which exploit the benefits of resonant operation and maintain stable performance. Resonant devices provide high sensitivity and convenient signal processing. The drawback of the method is the sensitivity to undesired environmental effects and aging. The environment induced degradation processes and the long-term stability of thin film resonators were investigated previously. The two major reliability problems were stiffening effect and degrading shock response, both affecting the mechanical resonance frequency. Based on these results, new, low-cost pressure sensors and accelerometers were designed and fabricated. The structures are based on locally reinforced silicon nitride membranes, and double-clamped 3-D silicon nitride bridges as sensing elements. This double mechanical structure allows separate optimization of the membrane and the bridges for the workload and for the most efficient driving and sensing. The 3-D bridges work as mechanical amplifiers, resulting in higher detection efficiency. The reliability tests indicated, that a low-cost atmospheric packaging is efficient, thus the bridges do not require vacuum encapsulation with multiple-wafer process. External mechanical and thermal excitation combined with piezoresistive and optical detection methods are implemented in the different sensors. Differential detection using reference resonators allow compensation for thermal, environment- and aging-induced stresses.

By investigating microaccelerometers with various configurations including the amplitude type and the resonant type, we summarize that dynamic behavior, geometry, structure rigidity and dimension are important considerations to design a microaccelerometer. In which, a linear dynamic response is better for its easiness to be processed, and a significant variation tendency in responding to the detected acceleration is required. A good geometry is necessary to decouple a detected acceleration, such as a 2D or 3D acceleration into two or three measurable independent accelerations components. In addition, a strong rigidity and stiffness are necessary to avoid the influence, such as the associated crosstalk from other non-interested acceleration, e.g., gravitation. Moreover, the dimensions of the structural components dominate the mechanical and electrical sensitivity of the device. We utilize these considerations to design a biaxil frequency-shifted microaccelerometer. This accelerometer is configured with a central proof mass connected via four identical and symmetrical beams with high-aspect ratio, and operates using natural frequency shift of the microbeam. The good performance of the accelerometer is verified by using analytical simulation and FEA (Finite Element Analysis). Moreover, to achieve a most sensitive structure, the best dimension arrangement of 1:2 for the ratio of the microbeam to the proof mass is also realized.

In this paper, the vibration characteristics of 2-DOF mechanical vibration absorber system are adopted to improve the mechanical sensitivity of a micro-electro-mechanical (MEMS) vibratory gyroscope sensor. The proposed gyroscope is basically composed of two oscillating masses that are interconnected with flexures. It can be shown that, at their resonance, the secondary mass will absorb most of vibration energy from the primary mass, thus resulting in the vibration amplification that is directly related to the mass ratio between the masses. Therefore, when an angular velocity is applied to such a gyroscope, most of the energy gained due to Coriolis force is transmitted from the primary element to the secondary element. As the primary mass is normally designed to be much bigger than the secondary mass, the Coriolis displacement of the secondary element will be amplified depending on the mass ratio. With the use of the secondary oscillating mass as a capacitive sensing element, the mechanical sensitivity of the gyroscope can be increased significantly. Modelling and simulation of a practical gyroscope design were conducted using ANSYS54 finite element code. The results are presented and verified with the theory.

In this paper, the configuration of combining holographic gratings and micromirror devices for optical add/drop functions is proposed for constructing OADM. Based on this architecture, a MEMS based vibrating micromirror device that is driven by electrostatic force in executing add/drop functions is designed and fabricated. Preliminary experiments had demonstrated the feasibility of the proposed system.

This paper proposes a design of a bistable micromechanism for the application of switching devices. The topology of a fully compliant four-bar mechanism is adopted herein. The central mass of the mechanism is employed as a carriage to carry switching components, such as mirror, electrical contact, etc. The equations that predict the existence of bistable states, the extreme positions of the motion range and the maximum stress states of members were derived. MUMPs provided by Cronos Integrated Microsystems fabricated the proposed micromechanisms for the purpose of verifying the theoretical predictions. Finally, an experimental rig was established. The bistable mechanisms were switched either by the probe or actuators to push the central mass. The experimental results demonstrated that the motions observed approximately met the predicted values.

In this study, we developed a torsional micromachined receiver array to generate acoustic wave based on Lorentz force. The receiver array is constructed by many micro mirror components with which two pair of leads were laid around each mirror edge. In each component, a direct and an alternating driving signal were applied to each pair of leads, respectively. The mirror components will then rotate to an angle and oscillate upon the application of a specific magnetic field induced by Lorentz force. The alternating signal drives the mirror to oscillate and to generate acoustic waves of the same frequency as the alternating signal. The strength of the alternating signal and the amount of the mirror components determine the power density of the acoustic waves. The direct signal is applied on one of the paired leads that transacts with the magnetic field. Lorentz force then rotates the mirror component to a torsional angle that is proportional to the direct signal strength. Therefore, under a specific static magnetic field, driving the mirrors with different direct signal may focus the acoustic waves. With the focusing mechanism, the acoustic wave is capable of scanning in various depths, which could be reached by continuously changing the direct signal strengths. Additionally, applying the direct signals based on appropriate timing will produce strong wave by reconstructed interference, and the acoustic waves will be focused effectively. The acoustic waves then have much higher resolution and can be utilized similar to light waves.

Rotman lenses have the potential to solve many problems associated with high frequency antenna arrays. Offering compact, rugged and reliable means of forming muli-beam, staring array sensing arrangements, these lenses may prove very useful if robust solutions to some important problems are to be found. This paper presents the performance of a Rotman lens design and discusses the challenges associated with the design of these lenses.

In this paper, we analyze the shape of the cylindrical micromirror, which directly defines the profile of the reflecting surface, and is very important for the function on focusing. A cylindrical micromirror can converge incident rays to a real focal line after reflection, namely angular focusing. Therefore, under specific design two cylindrical micromirrors, the primary and secondary, can converge incident rays into a real focal point after twice reflection. The curved shape of micromirror, formed due to the stress-induced bending of the bilayer microstructure upon release, has been theoretically analyzed and numerically simulated. The results show that the reflecting surface, especially at boundaries, is not perfectly cylindrical, while adding longitudinal frames can make some improvement.

The insertion loss is highly affected by the optical path length for 2D or matrix type free space optical switch. Since the v-groove width of conventional Si optical bench is more than 25% larger than the diameter of lens, it is almost impossible to make the optical bench that has the smaller lens pitch than its diameter. In addition, owing to 'convex corner effect', the completed optical bench has the different etched pattern than expected which also makes it difficult to align the optical components. In this paper, novel design and fabrication of Si optical bench is proposed to solve these problems. We arranged the lenses meanderingly so the lens pitch could be shortened remarkably. New method to make perfect optical bench by wet etch and deep RIE process is also proposed. To compare the simulation result with the experimental one, we made the in-line type optical bench. Its maximum optical path is about 38 mm which is the same as that of the proposed 16x16 free space optical switch. From the optical simulation, the insertion loss is less than 2 dB and it agrees with the measured value within the experimental error.

LIGA is a technology that offers significant advantages where high accuracy, high aspect ratio microstructures are required. The application of LIGA to the manufacture of real products has been delayed by technical problems that exist with the individual process steps and the limited availability of integrated facilities, enabling users to subcontract the complete manufacturing process. These problems have been dominated by the limited availability of high quality masks, long and expensive exposure at synchrotron radiation sources and the electrodeposition of thick stress-free layers. This paper describes the practical solutions developed at the Central Microstructure Facility, RAL, for the key process steps of manufacturing high precision gold-on- beryllium masks, exposure of SU-8 resist using a 2 GeV synchrotron, electrodeposition of deep ($GTR 500 mm), stress-free metal layers and resist stripping procedures fro 3 micrometers minimum features up to 500 mm deep on 4-6 inch wafers. A cost model shows that the reduction in the exposure time using SU-8 instead of PMMA resist may enable x-ray LIGA to be cost competitive with other techniques such as uv LIGA, DRIE or direct laser ablation.

A thin film airflow transducer based on the hot wire anemometer principle was designed using current MEMS modelling & simulation software. Flow sensors are commonly implemented with thermal isolation of the sensor from the bulk substrate mass using methods such as reverse side etching or sacrificial layers, however this paper will present a sensor relying on thermal insulation only. This insulation may be provided by layers of material exhibiting relatively poor thermal conduction characteristics such as silicon dioxide or polyimide, giving rise to a number of advantages such as removing the process of reverse side etching. Limiting fabrication to use of simple processes such as photolithography and sputtering/evaporative deposition also simplifies this design and assists in greatly increasing the compatibility with standard CMOS fabrication processes and materials. A combination of both theoretical computer modelling and physical fabrication and testing has been the approach to this research. Preliminary testing of this design has demonstrated small yet measurable temperature gradients across the device surface during steady state operation. The novel approach to this device is the investigation of pulsed operation, effectively a transient analysis that allows the thermal conduction effects of the bulk mass to be significantly reduced, leading to a significant increase of both efficiency and response time. Electro-thermo-mechanical and computational fluid dynamic analysis of the structure successfully model the thermal conduction, radiation and forced convection effects of the device during and after ohmic heating of the sensor's heating element.

The paper presents an one-dimensional model for the heat transfer in a limited but significant region of an actuator-sensor structure for the determination of fluid and flow characteristics. As an essential step for the designing process of this structure, the usefulness of the model in the framework of the structure's functionality is underlined. In the first part of the work, the main heat transfer mechanisms are detailed by qualitative and quantitative evaluations. The one-dimensional model is derived from the heat balance of the region we are interested in. In the second part of the work, we compare the data obtained by simulating this model with the experimental data we have. Also, some full three-dimensional simulations of the fluid flow and heat transfer we made using a commercial software package. Part of these numerical results are compared with the corresponding experimental data. The modeling errors are discussed for the both sets of comparisons. Finally, we comment the merits of the one-dimensional model versus the three-dimensional approach. The achieved results obtained herein might be directly used for various thermal based actuators and sensors for flow control and measurement both in micro and macro world.

Micromachined gyroscopes rely on tuned vibration mode frequencies to measure rotation rates and typically have complex modes of vibration for the mechanical microstructures. Although there are many reports on how to exactly tune the drive and sense modes of vibration to maximize sensitivity of micromachined gyroscope, there are only few reports on the detailed analysis of modes of vibration. Modes of vibration are strongly dependent on the design parameters of the mechanical structure of the gyroscope including the dimension of the proof mass, types and dimensions of the suspension, and residual mechanical stress of the high aspect-ratio polysilicon film used to form the microstructures of the micromachined gyroscope. In this paper, an electrostatic drive and capacitive sense in-plane decoupled gyroscope for measuring vertical angular velocity is proposed to study the effects of the geometrical variables on modes of vibration. Finite-element analysis (FEA) simulation was performed on simplifiedmodel of the in-plane decoupled micromachined gyroscope microstructure. For optimal result the drive-mode and sense-mode suspensions of the micromachined gyroscope should be fabricated from thick polysilicon microstructure to give large aspect ratio suspension systems for the in-plane decoupled micromachined gyroscope. Folded-beam suspension design is recommended for the drive-mode suspension in order to relieve the residual stress of the thick polysilicon film for high aspect-ratio micromachine dgyroscope. It is critical to control the process variations of the suspension beam dimension, especially the beam width variation in order to achieve the goal of accurately control resonant frequencies of micromachined gyrocope.

With the recent surge in popularity of RF and Microwave MEMS many different device topologies are being explored. Some devices provide large changes in capacitance, but lack the ability to provide a linear range of capacitance values between the minimum and maximum values of the device. We present a device design for a low-loss rotating MEMS tunable capacitor that once programmed to the required value consumes no power. This device design is transformed from gear structures currently designed in the SUMMiT process with modifications made so that the device may be used as a varactor. Modifications include alterations of physical structure, drive mechanism for programming capacitance value, and additional post processing steps needed to provide low-loss at RF and Microwave frequencies. Many different device structures are possible each with performance, potential reliability, and potential yield trade offs that must be considered. Post processing is required to add metal to provide sufficiently low loss for high quality components. Since device planarity is critical for operation, a novel post-process metal deposition technique for providing low stress metal was concieved. Additional modifications to compensate for polysilicon warpage are considered for future investigation. Simulation results based on high frequency full wave analysis software show a highly linear tuning range and a capacitance ratio approaching 6 to 1. A model is extracted from the scattering parameters provided by HFSS and then various device sizes and topologies are compared.

In the span of a few years, mobile multimedia communication has rapidly become a significant area of research and development constantly challenging boundaries on a variety of technological fronts. Video compression, a fundamental component for most mobile multimedia applications, generally places heavy demands in terms of the required processing capacity. Hardware implementations of typical modern hybrid codecs require realisation of components such as motion compensation, wavelet transform, quantisation, zerotree coding and arithmetic coding in real-time. While the implementation of such codecs using a fast generic processor is possible, undesirable trade-offs in terms of power consumption and speed must generally be made. The improvement in power consumption that is achievable through the use of a slow-clocked massively parallel processing environment, while maintaining real-time processing speeds, should thus not be overlooked. An architecture to realise such a massively parallel solution for a zerotree entropy coder is, therefore, presented in this paper.

Parallel multipliers are of increasing importance for VLSI design, largely driven by the significant increase in demand for computer graphics and digital signal processing. The fastest (and, when pipelined, most area-efficient) multiplier class is partial product reduction tree (PPRT) based multipliers. The previous best known heuristic for PPRT design (published by Stelling et al.) is capable of producing the fastest possible circuits but suffers an infeasible computational burden. This paper introduces some results which significantly reduce the search space of this heuristic. Consequently, the speed of netlist generation is increased, and the circuits generated retain optimal performance. In addition, larger optimal multipliers may be synthesised due to the easing of the computational burden.

In this paper, we report transient capacitance measurements performed on MOCVD-grown nominally undoped n-GaN Schottky diodes exposed to ⁶⁰Co gamma irradiation. Three radiation-induced defect levels are identifiable at an accumulated dose of 21 Mrad(Si) with thermal activation energies of 88+/- 7 meV, 104+/- 12 meV and 144+/- 13 meV, produced at a rate of 2.2x10^-3 cm^-1 per 1.25 MeV photon. The isochronal annealing behavior of these defects indicates that they are of similar nature, stable at temperatures < 100 C and disappear for annealing temperatures > 350 C. The carrier emission and annealing characteristics of these defects are consistent with previously identified nitrogen-vacancy related defects. Three deep-level defects present before irradiation exposure with activation energies of 254, 363 and 586 meV were found to remain unaffected for cumulative gamma-ray doses up to 21 Mrad(Si).

Camera-on-a-CMOS chip will be an inevitable component of future intelligent vision systems. However, up till now, the dominant format of data in imaging devices is still analog. The analog photocurrent or sampled voltage is transferred to the ADC via a column or a column/row bus. Moreover, in the active pixel configuration the area occupied by circuitry reduces significantly the fill factor, so that there are heavy constraints imposed on the size of the circuits used. In this paper a concept of back illuminated focal plane is presented. The system consists of two chips bonded face to face using Indium bumps. The top chip, which is the seeing chip, is thinned and the light signal is applied to the bottom surface. The bottom chip is the processing chip and it contains a distributed array of analog-to digital converters. As the seeing chip is fully dedicated to photosensors the fill factor can be increased from 25-40% possible on a single plane to over 95% with two planes. The analog-to-digital converters are algorithmic current-mode converters, where one-bit cell is implemented in the processing area facing one-pixel. Eight such cells are cascaded to form an 8-bit converter. As a result, a fully digital pixel readout is obtained.

In the present endeavour, force - deflection behavior of various piezoelectric actuator configurations has been analyzed for performance comparison. The response of stack actuator has been simulated using MATLAB Simulink, in a stack actuator-pendulum configuration. During simulation, stack actuator has been used in charge control feedback mode, because of the advantage of low hysteresis, and high linearity. The model incorporates three compensation blocks, viz 1) a PID position controller, 2) a PI piezoelectric current controller, and 3) a dynamic force feedback. A typical stack actuator, having 130 layers, 1.20x10^-4 m thickness, 3.46x10^-5m² cross sectional area, of PZT-5H type, has been utilized for simulation. The response of the system has been tested by applying a sinusoidal input of frequency 500 Hz, and waveform amplitude of 1x10^-3V.

Electrostatic micro-relays with elastically deformed anchor (ESRE) enable to lower operation voltage due to more efficient use of electrostatic and mechanical forces interaction peculiarities. It contains the anchor with movable electrode of plate shape fixed between elastic cantilever holders with force exceeding a critical one. According to stability theory, the sagged anchor gains sinusoid-like shape with a sag equal to inter-electrode gap and directed out of immovable electrode plane. The performed calculations of ESRE have given detailed information in numerical and graphical form on interaction of electrostatic forces and mechanical forces during the switch-on process of micro-relays with various technical parameters.

Single layer of aluminum film was sputter deposited on to (100) oriented 4 inch silicon wafer to study effect of film thickness, D.C. power and sputtering gas pressure on the film stress. The as-deposited stress appeared to be increasing as film thickness increases and argon pressure decreases. Thermal stress originated from difference in CTE and temperature variation during and after sputtering seems to be a main factor in room temperature sputter deposited aluminum films. From observation of temperature-stress behavior, it was found that the pure aluminum film has an elastic modulus of 56GPA and compressive yield strength of -100MPA. The yield strength was improved to about -175MPA by alloying with 3wt.%Ti. Titanium alloying also proved to be useful in extending linear elastic region before plastic deformation occurs. However, it was hard to determine the stress level with buckling phenomena of ring/beam microstructures because of imperfections such as stress gradient and thermal deformation. In stead, those diagnostic microstructures could be applied to give an information on whether a plastic deformation was introduced or not in a structure of specific dimension.

This paper presents a novel method for wafer-through interconnects via anisotropically etched groove in a (100)-silicon wafer. The idea is based on realization of interconnection lines on the inclined sidewalls of the anisotropically etched grooves, which are transferring the metallization to the backside of the wafer. The process itself is compatible with the standard semiconductor technology and can be applied at full wafer level, achieving in this way low packaging costs. All processes for interconnects are applied from the backside of the wafer at the packaging step, thus preserving the frontside of the wafer during processing from scratches and pollution. The key issue in the presented method is the photoresist coating of anisotropically etched grooves, which can be done by standard or electrodeposited photoresist. Further, methods to improve the photoresist uniformity over three-dimensional structures are discussed. Copper interconnects have been realized to show the feasibility of this wafer-through technique for frontside to backside electrical interconnections. Copper has been used for the metallization instead of aluminum. The thickness of the copper interconnects have been increased by copper electroplating to reduce further their electrical resistance and to increase their mechanical strength.

Microfluidic systems including microchannels and microvalves, fabricated by micromachining technology, are studied with approached models, either analytical or by simulation. The modelling of rectangular channel and passive valves is presented in this paper, which is divided in three parts. At first, the analytical modelling of a channel versus its shape factor and a normalisation of its fluidic comportment is presented. Then a description of the diffuser-nozzle valve is purposed by applying the general Bernoulli equation. The efficiency of this valve is found to be determined by the value of the shape factor and angle of the diffuser element. The third part is dedicated to numerical simulation of a Tesla diode and purpose an optimisation of its efficiency versus the Tesla geometry. Finally, the realisation and characterisation of prototypes are exposed. Characterisation were applied to rectangular channel and showed good agreement with the analytic modelisation. The analytic expressions, that have been found, can be used in simulations of the flow sensors through the construction of an equivalent electric circuit, and subsequently analysed using SPICE or similar tool Simulink Matlab.

This paper deals with a simple way for optimising the design of a valve-less micropump. The method is based on electric analogies. The micropump is compared to an electrical circuit similar to a RLC circuit. By this way, the fluidic resonant frequency of the micropump can be evaluated despite a non-linear working due to the used of micro-valve. The results are applied on the design of an electrostatic micropump with a specific electrode shape in order to control the micropump resonant frequency. In order to validate the modelling, a prototype of electrostatic micropump is realised. The micropump is composed of three different wafers associated by bonding techniques.

In this paper, we have proposed and designed the new structure of a RF-MEMS voltage tunable capacitor, which have two-movable parallel plates using electrostatic method and can be fabricated by the MEMS technology. Capacitance of the designed voltage tunable capacitor has from 1.0pF to 1.48pF as the applied bias voltage from 0.5V to 2.48V. And the results of the simulation data for designed tunable capacitor are shown by the graph. The effective area and the distance of the capacitor plates are 335x335micrometers ² and 1micrometers for 1pF.

This paper investigates the effect of gas flow in holes on the squeeze film damping of perforated structures. An infinite perforated plate with circular holes is analyzed with an analytical model. The results show that there is a minimum damping ratio for a certain size ratio. The corresponding hole size can be defined as a critical size. When the hole size is smaller than the critical size, the hole effect dominates. The damping ratio increases drastically with hole size decreasing when the size ratio keeps constant. Some finite two-dimensional structures are analyzed with an equivalent circuit model. Similar results are obtained. The finite two-dimensional structures and some quasi three-dimensional structures are also simulated with ANSYS/FLOTRAN. The results are presented.

While differential Hall measurements are a standard approach to determination of junction depth in multi-layer semiconductors, significantly more information can be obtained from magnetic field dependent differential Hall measurements. When such measurements are treated using Quantitative Mobility Spectrum Analysis (QMSA), detailed depth resolved profiling of both carrier concentrations and mobilities can be achieved, giving important data directly related to potential device performance. The doping profile is obtained by performing a series of etch-back experiments with magnetic field dependent Hall measurements performed between the etching steps. This technique is illustrated on a number of vacancy and gold doped Hg_1-xCd_xTe p-type epilayers, which have been partly or wholly converted to n-type by a reactive ion etching (RIE) process. The QMSA analysis reveals that there are several electron species present in the layers as well as the original p-type carrier. The electron species have been identified as low mobility surface electrons, and high and low mobility electrons located at various depths through the epilayer. It also indicates that the p-to-n conversion depths range from less than 0.5micrometers for vacancy doped Hg_0.7Cd_0.3Te material, to more than 17micrometers for Au-doped Hg_0.8Cd_0.2Te for the same type conversion conditions.