This paper discusses some reliability issues that play a role for capacitive RF MEMS switches. We describe how these degradation mechanisms affect the functioning of the switches. Also the methodology that can be used to test capacitive RF MEMS switches, including some packaging aspects, and dedicated instrumentation required to perform these tests are discussed.

In the future, MEMS switches will be important building blocks for designing phase shifters, smart antennas, cell phones and switched filters for military and commercial markets, to name a few. Low power consumption, large ratio of off-impedance to on-impedance and the ability to be integrated with other electronics makes MEMS switches an attractive alternative to other mechanical and solid-state switches. Radant MEMS has developed an electrostatically actuated broadband ohmic microswitch that has applications from DC through the microwave region. The microswitch is a 3-terminal device based on a cantilever beam and is fabricated using an all-metal, surface micromachining process. It operates in a hermetic environment obtained through a wafer-bonding process. We have developed PC-based test stations to cycle switches and measure lifetime under DC and RF loads. Best-case lifetimes of 10¹¹ cycles have been achieved in T0-8 cans (a precursor to our wafer level cap) while greater than 10¹⁰ cycles have been achieved in the wafer level package. Several switches from different lots have been operated to 10¹⁰ cycles. Current typical lifetime exceeds 2 billion cycles and is limited by contact stiction resulting in stuck-closed failures. Stuck-closed failures can be intermittent with a large number of switches continuing to operate with occasional sticks beyond several billion cycles. To eliminate contact stiction, we need to better control the ambient gas composition in the die cavity. We expect lifetime to improve as we continue to develop and optimize the wafer capping process. We present DC and RF lifetime data under varying conditions.

Shallow V type symmetric electrothermal actuators which have a central shuttle and overall lengths of ~610 μm, leg widths between 3 and 4.5 μm, and offset angles between 0.7 and 2.3° have been subjected to short term, high stress drive currents under different environmental conditions. For all the devices and all test conditions, ~200 mW power levels lead to plastic deformation both for DC actuation and square wave modulation at the limit of the device’s bandwidth. Also, it is noted that under vacuum conditions the hottest portions of the surface roughen significantly and there is significant discoloration of the silicon nitride under the device. SEM analysis of cleaved surfaces of these vacuum actuated devices shows significant near surface pitting.

COTS (Commercial-off-the-shelf) MEMS components are very interesting for space applications because they are lightweight, small, economic in energy, cheap and available in short delays. The reliability of MEMS COTS that are used out of their intended domain of operation (such as a space application) might be assured by a reliability methodology derived from the Physics of Failure approach. In order to use this approach it is necessary to create models of MEMS components that take into consideration environmental stresses and thus can be used for lifetime prediction. Unfortunately, today MEMS failure mechanisms are not well understood today and therefore a preliminary work is necessary to determine influent factors and physical phenomena. The model development is based on a good knowledge of the process parameters (Young’s modulus, stress...), environmental tests and appropriated modeling approaches, such a finite element analysis (FEA) and behavioural modeling. In order to do the environmental tests and to analyse MEMS behaviour, we have developed the Environmental MEMS Analyzer EMA 3D. The described methodology has been applied to a Commercial-off-the-shelf (COTS) accelerometer, the ADXL150. A first level behavioral model was created and then refined in the following steps by the enrichment with experimental results and finite element simulations.

Many promising applications of MEMS based devices are in critical systems. Hence, their reliability has become an important issue. The techniques used for the fabrication of these devices give rise to large residual stresses. This coupled with their high speeds of operation make them prone to fatigue failure. The focus of this work is the improvement of reliability under fatigue loading using multi-layers. This paper demonstrates that by adjusting the thickness ratios, the stress in a multi-layered resonator can be prevented from alternating. Moreover, the peak stress can be minimized and performance can be improved in harsh environments.

The purpose of this paper is to illustrate the approaches used to determine the location, character, and origin of failed superstructure elements within the Digital Micromirror Device and relationally to other types of MEMS and MOEMS devices. Since the Digital Micromirror Device is a very large field of movable mirrors that are essentially identical in appearance, some of those methods will include the uses of: failure mapping, digital imaging techniques, and explanations of precautions needed to ensure the result of the analysis is a correct answer to the questions asked.

Laser Doppler Vibrometry (LDV) is a widely accepted tool for dynamic characterization of MEMS. Using automated scan capability, the Polytec system can measure structural resonance and display out-of-plane deflection shapes with amplitudes down to the picometer level and frequencies to 30 MHz. By adding stroboscopic video microscopy for in-plane motion analysis, our combined Micro Motion Analysis (MMA) system is capable of three-dimensional dynamic characterization. The MMA system opens up new possibilities to measure in-plane actuators previously difficult or impossible for LDV measurements. To exemplify the use of this technology, we present characterization measurements on MEMS devices fabricated by Sandia National Labs SUMMiT V process. Multi-axis measurements reveal the complex motions exhibited by an electrostatic comb drive driven at resonance. Also, ultra-high resolution velocity measurements are made on passive cantilever structures oscillating under thermal excitation. Picometer resolution makes possible detection of these purely mechanical resonances. Both comb drive and cantilever data are used to determine mechanical properties important to evaluate the reliability of fabrication processes. This study demonstrates the unique performance of our hybrid LDV / strobe video measurement system for quick, accurate, high-resolution dynamic response measurements.

Novel nondestructive method based on low coherence optical interferometry for measurement of deep etched trenches in MEMs structures is presented. The proposed technique proves to provide very reproducible results and can be easily extended to metrology of other materials such as metals and dielectrics. We present results in real life semiconductor structures and discuss practical and fundamental limits of this technique

We have developed a multifunctional interferometric platform for testing MEMS/MOEMS, measuring the 3-D out-of-plane deflections and providing both material properties and motion behaviour of microdevices. Specific metrology procedures have been demonstrated to determine respectively and residual stress of silicon membranes compressively prestressed by SiO_xN_y PECVD deposition study of vibration modes of PZT microactuators as well as the expertise of Scratch Drive Actuators.

A new approach to vacuum packaging micromachined resonant, tunneling, and display devices will be covered in this paper. A multi-layer, thin-film getter, called a NanoGetter, which is particle free and does not increase the chip size of the microsystem has been developed and integrated into conventional wafer-to-wafer bonding processes. Experimental data taken with chip-scale packages using glass frit bonding between the Pyrex and silicon wafers, has resulted in silicon resonators in which Q values in excess of 37,000 have been obtained. Reliability data for vacuum-sealed diaphragms and resonators will be presented. Unlike previous reliability studies without getters, no degradation in Q has been noted with NanoGetter parts after extended high temperature storage. Applications for this technology include gyroscopes, accelerometers, displays, flow sensors, density meters, IR sensors, microvacuum tubes, RF-MEMS, pressure sensors and other vacuum sealed devices.

Wafer bonding has attracted significant attention in applications that require integration of Micro-Electro-Mechanical Systems (MEMS) with Integrated Circuits (IC). The integration of monolithic MEMS and electronic devices is difficult because of issues such as material compatibility, process compliance and thermal budget. It is important to establish a wafer bonding process which provides long-term protection for the MEMS devices yet does not affect their performance. The attentions for such integration are at the die level and wafer level. Recently, the trend is toward wafer-level integration as a cost effective solution to combine sensing, logic, actuation and communications on a single platform. This paper describes the development of low temperature bonding techniques for post-CMOS MEMS integration in system-on-chip (SOC) applications. The bonding methods discussed in this paper involve Benzocyclobutene polymer (BCB) as glue layer to joint two 200 mm wafers together. The bonding temperature is lower than 400°C. Four-point bending and stud-pull methods were used to investigate the mechanical properties of the bonding interfaces. These methods can provide critical information such as adhesion energy and bonding strength of the bonded interfaces. Initial test results at room temperature showed that the BCB bond stayed intact up to an average stress of 50 MPa. It was observed that the BCB bond strength decreased with increasing temperatures and the energy release rate decreased with decreasing BCB thickness.

The patterned getter film at wafer level has been proven to be the viable technical solution to integrate a getter film in vacuum packaged MEMS. The different MEMS vacuum bonding technologies such as eutectic, direct fusion and anodic bonding guarantee a suitable combination of time and temperature to properly activate the getter film. However, before any MEMS vacuum bonding process it has been discovered that a caustic chemical treatment of the getter film both cleans the film and enhances its performance without measurable degradation of its structural integrity. For example, caustic chemical treatment with SC1 with NH₄OH and SC2 with HCl did not affect the morphology and the sorption capacities of the getter film and significantly increased the sorption capacity. The getter film at wafer level can withstand also treatment with a highly aggressive HNO₃ process. Therefore, we demonstrated the full compatibility of the getter film towards both temperature and chemical treatment with regards to the activation and capacity of the getter film.

This paper reports the preliminary results for an on-going program in wafer-level MEMS package. In this particular paper, three closed-loop microheaters of 5μm, 7μm and 9μm width were designed. By reactive ion sputtering technique, two classes of samples were presented. The first one was first co-sputtered with nickel / chromium (Ni/Cr) alloy and then sputtered with gold(Au) metal as heating material; the second one was sputtered with Cr, tin (Sn) and Au respectively as heating material. The bonding of the former sample based on the Ni/Cr and Au heating material failed. The eutectic bonding experiment of the later sample based on the Cr, Sn and Au heating material by global heating method was completed in annealing oven at temperature of about 400 deg. C. for 20 minutes. The SEM testing result showed the eutectic bonding of Au-Sn by global heating was successful. More results will be reported in future.

Microsystem packages and package assembly processes have an enormous influence on the ability to successfully bring a microsystem product to market. Package and assembly processes can introduce both performance and reliability issues which can introduce significant delays in the product engineering cycle. Typically, thousands of devices must be made and tested to fully quantify the reliability of a microsystem product. While most microsystem products use package and package assembly technology adapted from the integrated circuit industry, the unique aspects of these devices requires unique package designs and unique implementation of the unit assembly processes. This paper discusses many of these unit processes, their adaptation to microsystem applications and the reliability issues that can be traced back to these processes. Solutions to these package assembly issues will also be presented.

Low temperature bonding techniques with high bond strengths and reliability are required for the fabrication and packaging of MEMS devices. Indium and indium-tin based bonding processes are explored for the fabrication of a flextensional MEMS actuator, which requires the integration of lead zirconate titanate (PZT) substrate with a silicon micromachined structure at low temperatures. The developed technique can be used either for wafer or chip level bonding. The lithographic steps used for the patterning and delineation of the seed layer limit the resolution of this technique. Using this technique, reliable bonds were achieved at a temperature of 200°C. The bonds yielded an average tensile strength of 5.41 MPa and 7.38 MPa for samples using indium and indium-tin alloy solders as the intermediate bonding layers respectively. The bonds (with line width of 100 microns) showed hermetic sealing capability of better than 10^-11 mbar-l/s when tested using a commercial helium leak tester.

In order to meet changing product demand and product quality requirements, Electronic manufacturers must rely more upon automation and Manufacturing Execution software. Manufacturing software systems enable the integration of quality data, process control and rapid product modeling and testing without sacrificing operator productivity.

MEMS technologies have been applied to a lot of areas, such as optical communications, Gyroscopes and Bio-medical components and so on. In terms of the applications in the optical communication field, MEMS technologies are essential, especially, in multi dimensional optical switches and Variable Optical Attenuators(VOAs). This paper describes the process for the development of MEMS type VOAs with good optical performance and improved reliability. Generally, MEMS VOAs have been fabricated by silicon micro-machining process, precise fibre alignment and sophisticated packaging process. Because, it is composed of many structures with various materials, it is difficult to make devices reliable. We have developed MEMS type VOSs with many failure mode considerations (FMEA: Failure Mode Effect Analysis) in the initial design step, predicted critical failure factors and revised the design, and confirmed the reliability by preliminary test. These predicted failure factors were moisture, bonding strength of the wire, which wired between the MEMS chip and TO-CAN and instability of supplied signals. Statistical quality control tools (ANOVA, T-test and so on) were used to control these potential failure factors and produce optimum manufacturing conditions. To sum up, we have successfully developed reliable MEMS type VOAs with good optical performances by controlling potential failure factors and using statistical quality control tools. As a result, developed VOAs passed international reliability standards (Telcodia GR-1221-CORE).

Previous research has attributed the fatigue susceptibility of silicon films to the sequential oxidation of the silicon and environmentally-assisted crack growth solely within the SiO₂ surface layer. This “reaction-layer fatigue” mechanism is only significant in thin films where the critical crack size for catastrophic failure can be reached by a crack growing within the oxide layer. Fracture mechanics analyses can provide important insight into the limitations of structural silicon films. In this paper, our current understanding of the reaction-layer fatigue mechanism will be reviewed. Current results suggest that surface oxide layer thicknesses as low as 10-20 nm may induce reaction-layer fatigue when considering failure of the specimen for a crack reaching the silica/silicon interface. In contrast, 3-fold thicker surface oxide layers are required for failure due to a crack within the oxide layer.

Factors affecting the fracture strength of single-crystal silicon membranes are assessed. These factors include: membrane shape at the membrane’s intersection with structural frames or sidewalls, membrane thickness, membrane surface roughness, membrane mis-orientation to the principal crystallographic axes, wafer starting material quality, membrane stress (or pre-tension), and microstructure and shape at bond interfaces, such as the anodic bond interface between membrane and Pyrex wafers. Measurements of fracture strength versus these factors are made. Direct measurements of stress are also made using micro-Raman techniques. Simulations of membrane structures are studied, in order to evaluate the measurements. The results indicate that the predominant factor affecting fracture strength is surface roughness.

In an effort to find ways to minimize the undesirable effects of thin metal film stress changes with time on MEMS reliability we have investigated stress relaxation of nanoscale A1 thin films. We have found that the relaxation is strongly dependent not only on temperature but on film thickness as well. Films 33, 107 and 205nm thick prepared by evaporation onto a silicon nitride membrane substrate were studied using membrane resonance to determine film stress. A single thermal cycle to 300°C was used to establish a stress in the aluminum films, after which the time dependence of the stress was measured for the three film thicknesses at 50, 75 and 100°C. The relaxation rate is highest for the highest temperature and the thinnest film. The time dependence is very well represented in all cases by an expression of the form dσ/dt = -A(σ-σ∞)ⁿ where σ∞ is the limiting stress below which the relaxation mechanism (which we attribute to dislocation motion) is unable to proceed. In all cases the value of n is greater than one so the decays are not exponential. A dislocation locking mechanism is suggested as a possible explanation for the observed thickness dependence.

We examine creep of thin film Au on curved bimaterial Au/Si microcantilevers. Time-dependent inelastic strains in the Au film lead to gradual changes in the microcantilever curvature over time. Curvature-temperature-time experiments are used to examine the effects of hold temperature and maximum annealing temperature on the inelastic response of the Au films. Experiments reveal inelastic strains in the Au films due to creep, recovery, and microstructural coarsening. At moderate hold temperatures, 30 °C < T < 175 °C, inelasticity in the Au films is observed to be a competition between creep and recovery. Creep strains are driven by tensile stresses in the film and serve to decrease the microcantilever curvature towards the equilibrium curvature of the underlying Si beam. Strains due to recovery of the metastable Au cause contraction of the film and the development of intrinsic tensile film stresses. The recovery leads to "anomalous’ changes in microcantilever curvature since the curvature gradually increases or decreases away from the equilibrium curvature of the underlying Si. The inelastic behavior of the Au film is shown to depend on annealing temperature through changes in initial film stress after thermo-elastic cooling and degree of recovery.

Special micro scanning mirrors have been designed for the investigation of torsional stress in micro-scale hinges made of crystalline silicon. The setup with precise logging of resonant frequency and deflection amplitude of the MEMS-scanners is described. First results on fatigue and fracture strength are presented. Fracture of torsion beams with 6.6 μm x 30 μm cross-section occurred at 2.0 GPa to 2.4 GPa. No sign of fatigue was observed in operation for 512 h at 1.4 GPa torsional stress in resonance at 2260.7 Hz oscillation frequency. Measured frequency variation was 0.06% without any trend.

Chemical and physical materials-aging processes can significantly degrade the long-term performance reliability of dormant microsystems. This degradation results from materials interactions with the evolving microenvironment by changing both bulk and interfacial properties (e.g., mechanical and fatigue strength, interfacial friction and stiction, electrical resistance). Eventually, device function is clearly threatened and as such, these aging processes are considered to have the potential for high (negative) consequences. Sandia National Laboratories is developing analytical characterization methodologies for identifying the chemical constituents of packaged microsystem environments, and test structures for proving these analytical techniques. To accomplish this, we are developing a MEMS test device containing structures expected to exhibit dormancy/analytical challenges, extending the range of detection for a series of analytical techniques, merging data from these separate techniques for greater information return, and developing methods for characterizing the internal atmosphere/gases. Surface analyses and data extraction have been demonstrated on surfaces of various geometries with different SAMS coatings, and gas analyses on devices with internal free volumes of 3 microliters have also been demonstrated.

Recent investigations have revealed the profound influence of adhesion, friction, and wear on the reliability of micro/nanoelectromechanical systems (MEMS/NEMS) devices. Studies of determination and suppression of these failure mechanisms are critical to improving the reliability of MEMS/NEMS. Using atomic force microscopy (AFM), researchers have developed the methodology to study the micro/nanotribological and mechanical behavior of one of the commercial MEMS - digital micromirror devices (DMD). Surface roughness, adhesion, friction, and wear properties of the contacting elements of the DMD lubricated by a self-assembled monolayer (SAM) have been extensively studied. Potential mechanism for micromirror stiction accrual has been suggested in light of the findings. In addition, the molecular level adhesion, friction, and wear performance of SAMs have been also investigated using AFM. The molecular tribological mechanisms of SAMs have been discussed to aid the design and selection of proper lubricants for MEMS/NEMS.

The adhesion and friction between pairs of self-assembled monolayers (SAMs) of alkylsilane chains on a silicon dioxide surface are studied using molecular dynamics simulations. We study chains with n=6, 8, 12, and 18 carbons in the backbone for both fully packed and defected monolayers. The defects are introduced by the random removal of chains from a well-ordered crystalline substrate. The adhesion force between monolayers at a given separation is found to increase monotonically with chain length and with coverage for a fixed chain length for the crystalline substrate. Friction simulations were performed at a relative shear velocity of 2 m/s at constant applied loads between 200 and 600 MPa. Stick slip motion is observed at full coverage, but disappears with the inclusion of 10% defects. We find that with the addition of random defects, the friction becomes insensitive to both chain length and defect density.

Reliability of MEMS is a major concern for the commercialization of laboratory prototypes. Surface adhesion or stiction strongly affects the reliability of MEMS devices which have sliding or rubbing contacts. Determination of adhesion energies, adhesion forces, and pull-off forces are important for predicting stiction in MEMS. We present an experimental technique to estimate the pull-off forces for MEMS surfaces. Polysilicon microcantilevers were electrostatically actuated using gradually varying voltages. A hysteresis was observed in the voltage at which the tip of the cantilevers made and broke contact with the substrate. Pull-off forces were estimated from the hysteresis in the voltage values using a strain energy formulation. The pull-off forces for microcantilevers dried out of isopropyl alcohol and repaired using laser irradiation were estimated to be in the range of 45-121 nN. The role of adhered length, variable external loading, and actuating signal on in-use stiction is also investigated. From our experimental results, we demonstrate an empirical approach to predict in-use stiction of microcantilevers.

A carbon nanotube-based high current density electron field emission source is under development at Jet Propulsion Laboratory (JPL) for submillimeter-wave power generation (300 GHz to 3 THz). This source is the basis for a novel vacuum microtube component: the nanoklystron. The nanoklystron is a monolithically fabricated reflex klystron with dimensions in the micrometer range. The goal is to operate this device at much lower voltages than would be required with hot-electron sources and at much higher frequencies than have ever been demonstrated. Both single-walled (SWNTs) as well as multi-walled nanotubes (MWNTs) are being tested as potential field-emission sources. This paper presents initial results and observations of these field emission tests. SWNTs and MWNTs were fabricated using standard CVD techniques. The tube density was higher in the case of MWNT samples. As previously reported, high-density samples suffered from enhanced screening effect thus decreasing their total electron emission. The highest emission currents were measured from disordered, less dense MWNTs and were found to be ~0.63 mA @ 3.6 V/μm (sample 1) and ~3.55 mA @ 6.25 V/μm (sample 2). The high density vertically aligned MWNTs showed low field emission as predicted: 0.31 mA @ 4.7 V/μm.

We have applied digital holography (DH) as interferometric tool for measuring the out of plane deformation of Micro-Electro-Mechanical structures. DH has been adopted as method for determining with high accuracy deformations due to the residual stress introduced by fabrication process evaluating MEMS behavior subjected to thermal load. A thermal characterization of these structures requires to cope two fundamental problems. The first one regards the loss of the focus due to thermal expansion of the MEMS sample support. With an out-of-focus image, a correct reconstruction of the sample image can not be obtained. To overcome the problem an auto-tracking procedure has been adopted. The other problem regards the direct comparison of images reconstructed at two different distances. In fact, in DH the numerical reconstruction image is enlarged or contracted according to the reconstruction distance. To avoid this problem, we have adopted a novel but very simple method for keeping constant the image size by imposing the reconstruction pixel constant through the fictitious enlargement of the number of the pixel of the recorded digital holograms. These procedures have been employed in order to characterize MEMS with different shapes and dimensions. The measured profiles obtained by DH can be employed to evaluate both the residual stress induced during the fabrication processes and its dependence on the temperature.

A New Polarimetric method for trench depth monitoring in micromachining applications is presented. As compared to the previous innovative and patented Twin-Spot interferometric technique developed by the Thin Film Division of Jobin Yvon, this new method allows an absolute and accurate trench depth monitoring suitable for Bosch process with no external triggering.

We introduce and demonstrate a new metrology method applicable for 3-dimensional (3D) measurements, based on common-path phase-shift interferometry. The method includes a unique optical setup in which wavefront modifications are applied over spatial regions of the wavefront reflected from an inspected object, and proprietary algorithm is used to fully reconstruct the reflected wavefront and thus the sample topography and reflectivity. This 3D measurement method was implemented into a measurement system, consisting of a measurement head integrated with a white-light microscope, using the latter as its imaging system. The system has sub nano-meter Z-axis accuracy, independent of the optical magnification. Other advantages of the technique are rapid real-time data acquisition, immunity to noise and vibration, small size, no moving parts, ability to work in various lateral magnifications, and versatile (reflectance or transmittance) optical imaging. The system’s small footprint, insensitivity to vibrations and operation simplicity, make it suitable to measure MEMS components in production environments and in conjunction with other probing systems.

Accurate determination of the as-built geometry of micro-electro-mechanical systems (MEMS)is important given the magnitude of the geometric uncertainty relative to the dimensions of these devices. A method for determining geometric process errors in MEMS fabrication from measurements of the resonant frequencies of simple structures is presented. This method provides a way to determine the process offset (the difference between the design width of a structural element and the as-built width) and, in the ideal case, the average angle of the side-walls of the films involved. An important feature of the approach presented is that by using frequency ratios, neither the elastic modulus nor the mass density of the film need be known a priori. This paper also introduces a robust design technique for MEMS subject to the inherent geometric and material uncertainties discussed previously. Although a range of design tools have been developed for MEMS, little has been done to account for the uncertainties associated with MEMS fabrication. The robust design problem we pose is to minimize the expected variance between the specified target system performance and the actual performance that a particular realization would be expected to exhibit. This robust design problem can be written as a constrained minimization. We consider a subset of these problems and develop an algorithm to minimize rational polynomial functions subject to polynomial inequality constraints. The details of the algorithm are presented and we verify its performance by examining the design of lateral resonators with specified resonant frequency. This example shows that the robust design nominally meets the target performance and is significantly less sensitive to geometric uncertainties than typical designs.

The growing place of electronics devices in our society increases the demand of small devices such as RF filters, time references and oscillators. The aim of this work concerns the design and characterization of a new kind of crystalline silicon microresonator fabricated using a DRIE (Deep Reactive Ion Etching) technique. This device can be fabricated by IC compatible techniques. This kind of microresonators is electrostatically actuated and uses a contour or Lamé mode as fundamental mode of vibration. Its size gives the resonant frequency and behavior. The mechanical characterization of one microresonator is carried out using an optical bench set-up. The first results obtained on a device show a high Q factor in air close to 1000 at the resonant frequency of 10.3 MHz.

Among the current commercial micromachined devices, pressure sensors are by far the most successful and popular products. They work to sense the displacement-induced stresses of a silicon membrane with the thickness at the micro-scale. The miniature dimension of such devices, coupled with the demand of accurate deflection measurement for performance characterization, make suitable metrological tools in immediate need. In this paper, we present a digital micro-holo interferometric method for realizing highly sensitive measurement of the full-field displacement over the global test structure. Through the analysis on the system principles, the pressure-induced membrane deflection are accurately measured, and further determination of strain and stress is accomplished based on the verified FE model. From the obtained stress-pressure relation, the sensitivity of the pressure sensor is thus characterized.

The major factor affecting the high performance applications of the piezoresistive pressure sensor is the temperature dependence of its pressure characteristics. The influence due to temperature variation is manifested as a change in the span, bridge resistance, and offset of the sensor. In order to reduce the thermal drifts of the offset and span of the piezoresistive pressure sensor, a Half-Bridge-Compensating (HBC) technique is presented in this paper. There are many advantages such as the temperature compensation of the sensor (typically lower than 1%), and a simple and low cost application circuit. The theoretical analysis and experimental results show that both the output voltage and zero offset drift are much improved by the first-order HBC technique. The experimental results are matched to our theoretical analysis.

This article describes a planar distortion quantification method for PDMS stamps used in soft lithography by introducing an angular parameter θ; the distortion θ is proportional to planar distortion in magnitude. We employ this method to evaluate PDMS stamps planar distortions supported on different treated glass with Micron XYZ Scope measurements. The average planar distortion of individual pattern (absolute distortion θ₁) and their pattern-to-pattern distortion (relative distortion θ₂) of PDMS stamps were determined by angular discrepancies (θ). The planar distortion quantification was evaluated among four different PDMS stamps affixation treatments, and the PDMS stamps supported on silane-modified glass showed strong binding and minimal planar distortion, its absolute angular distortion θ₁ was 3.98x10^-3 and relative angular distortion θ₂ 1.22x10^-3. Such distortion quantification agreed with the results of linear and area shrinkages on the stamps surface patterns, the results showed high reliability and fidelity of PDMS stamps and similar elastomer micro-patterns supported on silane-modified glass by photo lithographic microfabrication method and their promising prospects for on-chip synthesis of DNA microarray and bio-devices fabrication in soft lithography. The distortion evaluations demonstrate a versatile method for quantifying and comparing planar distortions among patterns as well as screening elastomer stamps support in soft lithography.