Surface Micromachining Technology Research Articles

System on chip thermal vacuum sensor based on standard CMOS process

An on-chip microelectromechanical system was fabricated in a 0.5 μm standard CMOS process for gas pressure detection. The sensor was based on a micro-hotplate (MHP) and had been integrated with a rail to rail operational amplifier and an 8-bit successive approximation register (SAR) A/D converter. A tungsten resistor was manufactured on the MHP as the sensing element, and the sacrificial layer of the sensor was made from polysilicon and etched by surface-micromachining technology. The operational amplifier was configured to make the sensor operate in constant current mode. A digital bit stream was provided as the system output. The measurement results demonstrate that the gas pressure sensitive range of the vacuum sensor extends from 1 to 105 Pa. In the gas pressure range from 1 to 100 Pa, the sensitivity of the sensor is 0.23 mV/ Pa, the linearity is 4.95%, and the hysteresis is 8.69%. The operational amplifier can drive 200 ω resistors distortionlessly, and the SAR A/D converter achieves a resolution of 7.4 bit with 100 kHz sample rate. The performance of the operational amplifier and the SAR A/D converter meets the requirements of the sensor system.

Evoking and Resolving Quantal Neurotransmitter Release on a Microchip

A microchip that facilitates in-vitro electrical and electrochemical measurements of individual cells and cell clusters was fabricated using surface micromachining and thick film technologies. In the present study, the device was applied towards the detection of exocytotic events from electrically stimulated rat pheochromocytoma (PC12) cells. Using device microfluidics, cells were positioned in a recording chamber over a 5 μm × 10 μm gold working electrode (WE). Channel dimensions (10 μm deep × 10 μm wide) ensured a tight fit for the ∼12 μm diameter PC12 cells in the chamber resulting in direct contact of the cells with the WE. This proximity allowed for quantal resolution of catecholamine release events from the cells and corresponding analysis of release kinetics and quantal size. Cells were stimulated through the application of sinusoidal voltage waveforms across axially-positioned, extracellular electrodes. In this manner, patterned extracellular gradients were generated across the cell thereby resulting in membrane depolarization. To facilitate interpretation of the stimulating electric field in relation to the cell and subsequent dopamine release, quasi-static electromagnetic FEM models were generated using COMSOL Multiphysics software. Upon depolarization, simultaneous chronoamperometric recordings at the WE confirmed stimulus-triggered dopamine release from the cells with a small subset of cells exhibiting release that modulated with the depolarizing cycle of the sinusoidal stimulus. It is anticipated that such a chip could provide a semi-automated alternative to the conventional, labor-intensive carbon fiber electrode (CFE) approach to neurotransmitter measurement.This work was supported in part by the National Institutes of Health, NIDCD R01 DC04928 and by National Science Foundation, IGERT NSF DGE-9987616.

用于投影显示的光栅光调制器

A novel grating light modulator for projection display is introduced. It consists of an upper moveable grating, a bottom mirror, and four supporting posts between them. The moveable grating and the bottom mirror compose a phase grating whose phase difference is controlled by the actuating voltage. When the phase difference is 2k\pi, the grating light modulator will switch the incident light to zero-order diffraction; when the phase difference is (2k-1)\pi, the grating light modulator will diffract light to first-order diffraction. A 16\times16 modulator array is fabricated by the surface micromachining technology. The device works well when it is actuated by a voltage with 1-kHz frequency and 10-V amplitude. The fabricated grating light modulator can show blackness and brightness when controlled by the voltage. This modulator has potential applications in projection display system.

Design of a Hybrid-Type Electrostatically Driven Microgripper Integrated Vacuum Tool

This work is focused on design and fabrication of a hybrid-type electrostatic silicon microgripper integrated vacuum tool. Vacuum tools are integrated in this novel microgripper in order to improve its pick and place capability. Surface and bulk micromachining technology is employed to fabricate the microgripper from single crystal silicon wafer (i.e., no silicon on insulator wafer is used). And the bonding technology is used to form the gas pipes for the vacuum tool. The linear motion of the microactuator is converted into a rotational gripping motion by a system of spring beams. At a driving voltage of 80V, a deflection of 25μm at the arm tip of the gripper is achieved.

Development of a MEMS Electrical Inertia Micro-switch Based on Non-silicon Substrate

Based on non-silicon surface micromachining technology, a simple but reliable micro electro-mechanical system (MEMS) electrical inertia micro-switch with single sensitive direction and reverse impact protection is designed and fabricated on glass substrate. In this design, conjoined serpentine springs are used to fix and suspend the mobile electrode (mass) and blocks are used to protect the device against reverse impulse. The switch is laterally driven (i.e. its sensitive direction is parallel to the substrate). Fabrication is carried out by low-cost and convenient multi-layer electroplating technology. The relationship between threshold acceleration and mass thickness has been investigated by theoretical analysis and finite element analysis (FEA) simulation. After fabrication and packaging, micro-switches are tested by using drop weight. The results show that the threshold accelerations distribute between 58g and 72g, which basically fulfils the expected 60g; and the response time to 100g half-sine waved shock is in the order of 10–4 s, which is in agreement with simulation result.

Micro Fabry Perot light modulator for flat panel display

A new type of Fabry Perot light modulator for displays based on micro-electro-mechanical system technology is proposed. Multiple beam interference theory is used to design the modulator and analyze its characteristics. If Fabry Perot cavity length is one-quarter of the incident wavelength, the transmitted light is blocked by the modulator, and the modulator, which is illuminated from its backside, appears black. If the Fabry Perot cavity length is 0 or one-half of the incident wavelength, light may transmit the Fabry Perot modulator from its backside, and the modulator appears bright. Hence, the modulator may be used for flat panel displays. In this paper one Fabry Perot light modulator based on surface micromachining technology is introduced. The designed modulator has a contrast ratio of 150 and can theoretically be driven by a voltage of 2.4 V.

Floating-Disk Parylene Microvalves for Self-Pressure-Regulating Flow Controls

This paper presents the first parylene-based floating-disk microvalve with self-pressure-regulating characteristics for various microfluidic applications. By incorporating a free-floating disk diaphragm with no anchoring/tethering structures to constrain its movement, the microvalve realizes configurable pressure-based flow-shunting functions in a stand-alone fashion. Its passive operation eliminates the need for power sources or the external actuation of the device. A multilayer polymer surface-micromachining technology is utilized for device fabrication by exploiting parylene C (poly-chloro-p-xylylene) as the biocompatible structural material for high mechanical compliance as compared with other conventional thin-film materials. Experimental results successfully demonstrate that the in-channel microvalves control water flows in the following two different shunt designs: 1) a nearly ideal regular check valve with zero forward-cracking pressure, zero reverse leakage, and 1.25 times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> - 2.09 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> Nldrs/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> (0.03-0.05 psildrmin/muL, 1.55-2.59 mmHgldrmin/muL) of fluidic resistance; and 2) a pressure-bandpass check valve with 0-100 mmHg and 0-10 muL/min of pressure and flow rate regulation ranges, respectively, as well as 4.88 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> Nldrs/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> (0.12 psi middotmin/muL, 6.08 mmHg middotmin/muL) of fluidic resistance in the forward conductive region. Such a biocompatible and implantable microvalve has the great potential of being integrated in microfluidic systems to facilitate effective microflow control for lab-on-a-chip and biomedical applications. [2008-0055].

λ/4 흡수층 구조를 갖는 NDIR 이산화탄소 가스센서용 적외선 센서의 제조 및 특성

A noble infrared <TEX>$\lambda/4$</TEX> absorbing structure using metal reflector was studied for uncooled infrared sensors. This paper described the design and the fabrication of IR uncooled detectors which were composed of 21 by 21 elements using the surface micromachining technology. The characteristics of the array were investigated in the spectral region of 4.26 <TEX>${\mu}m$</TEX>. The fabricated detectors exhibited the thermal mass of <TEX>$9.75\times10^{-9}$</TEX> J/K, the thermal conductance of <TEX>$1.31\times10^{-6}$</TEX> W/K, the thermal time constant of 7.4 ms, the responsivity of <TEX>$1.07\times10^5$</TEX> V/W and the detectivity of <TEX>$1.04\times10^9$</TEX> <TEX>$cmHz^{1/2}/W$</TEX>, at the chopper frequency of 10 Hz and the bias current of 9.22<TEX>${\mu}A$</TEX>. Finally the absorptance efficiency of <TEX>$\lambda/4$</TEX> absorbing structure was about 23.2 % higher than that of absence absorbing structure.

Investigation of RF sputtered PSG films for MEMS and semiconductor devices

In this work, we report the preparation of phospho-silicate-glass (PSG) films using RF magnetron sputtering process and its application as a sacrificial layer in surface micromachining technology. For this purpose, a 76 mm diameter target of phosphorus-doped silicon dioxide was prepared by conventional solid-state reaction route using P 2O 5 and SiO 2 powders. The PSG films were deposited in a RF (13.56 MHz) magnetron sputtering system at 200–300 W RF power, 10–20 mTorr pressure and 45 mm target-to-substrate spacing without external substrate heating. To confirm the presence of phosphorus in the deposited films, hot-probe test and sheet resistance measurements were performed on silicon wafers following deposition of PSG film and a drive-in step. As a final confirmatory test, a p–n diode was fabricated in a p-type Si wafer using the deposited film as a source of phosphorus diffusion. The phosphorus concentration in the target and the deposited film were analyzed using energy dispersive X-rays (EDAX) tool. The etch rate of the PSG film in buffered HF was measured to be about 30 times higher as compared to that of thermally grown SiO 2 films. The application of RF sputtered PSG film as sacrificial layer in surface micromachining technology has been explored. To demonstrate the compatibility with MEMS process, micro-cantilevers and micro-bridges of silicon nitride were fabricated using RF sputtered PSG as a sacrificial layer in surface micromachining. It is envisaged that the lower deposition temperature in RF sputtering (<150 °C) compared to CVD process for PSG film preparation is advantageous, particularly for making MEMS on temperature sensitive substrates.

A MEMS Inertia Switch With Bridge-Type Elastic Fixed Electrode for Long Duration Contact

A multilayer structural inertia microswitch with a bridge-type elastic fixed electrode for long duration contact has been designed and fabricated based on surface micromachining technology. The microswitch mainly consists of a suspended thick proof mass as a movable electrode and two parallel elastic beams with holes as a fixed electrode. The proof mass is designed to be much thicker than attached snake spring section. As a new type of fixed electrode, the bridge-type elastic beams can effectively improve the contact of the microswitch. The packaged microswitch (3.2 times 2.1 times1.3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) has been tested and characterized by a dropping hammer system. The response time and the contact time of the microswitch are about 0.25 ms and 12 mus, respectively, when 100 g acceleration is applied, which indicates a better contact effect than current reported switches. Dependence of the contact time on the thickness of the parallel beam under applied acceleration of 100 g has been discussed. The contact time increases as the thickness of the parallel elastic beam decreases. The test data have an agreement with dynamic finite element simulation results.

Design, Modeling, and Demonstration of a MEMS Repulsive-Force Out-of-Plane Electrostatic Micro Actuator

An analytical model is developed for a two-layer repulsive-force out-of-plane micro electrostatic actuator by using conformal mapping techniques. The model provides the means to establish the performance characteristics in terms of stroke and generated force of the actuator and is used to develop design and optimization rules for the actuator. Numerical simulations were conducted in order to verify the analytical model. A simple physical model is also presented that explains the mechanism for generating the repulsive force. A Multi-User-MEMS-Processes repulsive-force out-of-plane rotation micromirror is developed to experimentally verify the analytical model and to demonstrate the repulsive-force actuator's capability of driving large-size rotation plates by using surface micromachining technology. Experimental measurements show that the repulsive-force rotation micromirror with a size of 312 mum times 312 mum achieved a mechanical rotation of 0deg-2.1deg at a dc driving voltage of 0-200 V. The micromirror achieved an open-loop settling time of 2.9 ms for a mechanical rotation of 2.3deg and an open-loop bandwidth of 150 Hz (-3 dB).

Two-dimensional grating light modulator for projection display

A novel two-dimensional (2D) phase grating light modulator for projection display is proposed. It consists of an upper moveable grating, a bottom mirror, and four supporting posts between them. After the driving voltage is applied to the modulator, the upper grating will move down, which induces a phase difference and, therefore, leads to a controlled variation of its diffraction pattern. Optical characteristics of the modulator and the modulator array are analyzed with Fourier optics theory. The analysis shows the incident light will be switched from its zero order diffraction fringe to the first order diffraction fringe when the phase difference between the moveable grating and the bottom mirror changes from 2 pi to pi. The diffraction pattern of the light modulator array is the coherent superposition of all single modulators. A 16 x 16 modulator array is fabricated by surface micromachining technology. The test result shows that the device works well when it is actuated by a voltage with a 1 kHz frequency and 10V amplitude. Both theoretical analysis and experiment results indicate that the 2D phase grating light modulator has potential application in a projection display system.

Surface Micromachining Polymer-Core-Conductor Approach for High-Performance Millimeter-Wave Air-Cavity Filters Integration

This paper presents a novel approach to integrate high-performance millimeter wave filters on top of wafers. The proposed method eliminates the dielectric loss by elevating cavity-based filters into the air with the aid of the polymer-core conductor surface micromachining technology. The electrical fields of the cavity are thus entirely in air. A coplanar waveguide input and output interface is designed for easy integration with other planar electronics. Several 60-GHz (V-band) air-cavity filters with superior performances, including two two-pole filters and one four-pole transmission zero filter using a novel capacitive coupling scheme, are developed and characterized to demonstrate advantages of the proposed technology. The filters exhibit excellent performances. Insertion losses as low as 1.45 dB for a two-pole filter and 2.45 dB for a four-pole transmission-zero filter have been observed at 60 GHz. Design curves and parametric analyses are included to help readers better understand key factors in optimizations. The proposed technology is capable of integrating high-performance millimeter-wave cavity filters on top of wafers, while providing easy integration with other electronic components.

Fabrication of a MEMS inertia switch on quartz substrate and evaluation of its threshold acceleration

Based on surface micromachining technology, a micro-electro-mechanical system (MEMS) inertia switch with single sensitive direction and reverse impact protection has been designed and fabricated on quartz substrate. The switch is laterally driven (i.e. its sensitive direction is parallel to the substrate plane), in which the conjoined snake springs are used to fix and suspend the movable electrode (i.e. proof mass), and blocks are used to protect the device against reverse impact. The relationship between the threshold acceleration ath and the intrinsic frequency ω0=k/m has been investigated by theoretical analysis and finite element simulation, respectively, based on which the geometrical parameters of the switch can be decided to meet design objective. The proof mass thickness H was chosen as a variable, as the micro-fabrication of the device was carried out by low-cost and convenient multi-layer electroplating technology, where H can be easily adjusted while the plane geometry remains the same. The stress distribution of the switch in the contact process was also simulated. Packaged micro-switches were tested by dropping hammer experiments, which generated half-sine wave acceleration as in reality. The measured threshold acceleration generally met the design objective of 60g and the response time was in the order of 10−4s, both agreed with the simulated results.

An Integrated Surface Micromachined Convex Microhotplate Structure for Tin Oxide Gas Sensor Array

This paper describes the fabrication process for a novel convex microhotplate (MHP) structure using surface micromachining technology. The process is used to fabricate an integrated 4times4 tin oxide gas sensor array. Surface micro-machining is selected for its simplified process and CMOS compatibility. However, limited sacrificial layer thickness usually leads to higher power consumption. In this work, a convex MHP structure is developed to increase the thermal efficiency, which is critical for large dimension and low-power gas sensor array integration. Before the structure release process, 700degC-950degC annealing process was carried out on the 190 times190 mum2 MHP with 2.8 mum polysilicon sacrificial layer. It is shown that higher annealing temperature leads to lower tensional stress of the MHP membrane and larger curvature of the released structure, which enables higher thermal efficiency. Among the four annealing temperatures, the 950degC annealed MHP has the largest curvature of 2.438 cm-1 and the highest thermal efficiency of 13degC/mW. Experimental results showing the responses of the sensor array to different combustible gases are also illustrated in this paper. Comparison of power consumption with other designs reported in the literature illustrates the effectiveness of the proposed process.

Ultrathick and High-Aspect-Ratio Nickel Microgyroscope Using EFAB Multilayer Additive Electroforming

This paper presents a new approach for the development of a microgyroscope that has a 240-mum-thick multilayer electroformed-nickel structural mass and a lateral aspect ratio greater than 100. The gyroscope is fabricated using commercial multilayer additive electroforming process EFAB of Microfabrica, Inc., which allows defining the thickness of different structural regions, such as suspensions, proof mass, and capacitive electrodes, unlike many classical surface-micromachining technologies that require a uniform thickness for the structural features. The capacitive gaps of the gyroscope are designed to be laying parallel to the substrate plane and can be set as small as 4 mum, and therefore, the lateral aspect ratio, which is defined as the ratio of the overlap length of capacitor plates to the gap spacing, can easily exceed 100. The high capacitive aspect ratio, multilayer capacitors, and thick proof mass altogether yield a highly sensitive gyroscope for in-plane angular-rate measurements. Characterization of the fabricated gyroscope using a very simple capacitive interface circuit constructed from standard IC components yields a measured mechanical sensitivity of 65 muV/(deg/s) and a noise equivalent rate of 0.086deg/s at atmospheric pressure in a bandwidth of 1 Hz. The response bandwidth is limited to 100 Hz when the resonance frequencies of the drive and sense modes are matched by electrostatic tuning. The measured stability of the drive-mode resonance frequency is better than 0.1% within a 40-h period, demonstrating reliability of electroformed nickel of EFAB process. In addition, the mechanical quality factor of the sense mode reaches 2000 at 20-mtorr vacuum, verifying the quality of structural nickel. The resonance-frequency variations of the drive and sense modes with respect to increasing temperature are characterized to be smaller than 1 and -2 Hz/degC, respectively, in the -40-degC to +85-degC measurement range. The gyroscope performance can be further increased by reducing the minimum capacitive gaps, by increasing the number of stacked layers, by using a nickel-alloy structural layer with better mechanical properties, and by using a dedicated CMOS-application-specified integrated circuit which are under consideration.

A High-$Q$ Millimeter-Wave Air-Lifted Cavity Resonator on Lossy Substrates

In this letter, a 3D high-quality-factor millimeter- wave cavity resonator is integrated on the lossy soda-lime glass substrate utilizing surface micromachining technologies. With a height of 300 mum, the air-lifted cavity features a measured <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of at least 219 at 30 GHz, demonstrating an improvement by almost an order of magnitude with respect to respective planar resonators on the same substrate. The 3D cavity is monolithically integrated on the top of the substrate, with its side walls consisting of two rows of metalized pillars, while a weak coupling excitation scheme is used to extract the quality factor. This high performance cavity can be easily integrated with other monolithic integrated circuits and planar mm-wave components in multilayer modules.

Design, simulation and characterization of an inertia micro-switch fabricated by non-silicon surface micromachining

A multilayer structural inertia micro-switch with conjoined snake springs has been designed and successfully fabricated based on non-silicon surface micromachining technology. The micro-switch consists mainly of a suspended thick proof mass as a movable electrode that is located above the supporting layer, and an elastic beam with holes as a fixed electrode that is some distance above the proof mass. The designed proof mass is much thicker than the conjoined snake spring section. This conformation benefits the improvement of its sensitivity and the contact effect, while protecting the switch against severe shock damage from intensive impact of the switch contacts. The fabricated prototype micro-switch has been tested and characterized. The result indicates that the response time and the contact time of the micro-switch are about 0.40 ms and 12 µs, respectively, when a 100g acceleration is applied, which shows relatively better sensitivity and contact effect. This result agrees with that of dynamics finite-element contact simulation about the designed micro-switch. Besides, no severe plastic deformation occurs to springs or elastic beams after over 10 000 dropping tests in the optical profiling characterization. The fabricated micro-switch shows satisfactory mechanical behavior.

Surface micromachining technology with two SU-8 structural layers and sol–gel, SU-8 or SiO2/sol–gel sacrificial layers

The development reported herein is that of a surface micromachining technology using two SU-8 layers as a structural material. Three different processes are presented and discussed: the first process makes use of a sol–gel as the sacrificial layer; the second process utilizes the SU-8 itself as the sacrificial layer; the third process utilizes silicon dioxide as the first sacrificial layer and the sol–gel as the second sacrificial layer. These three processes are adapted for one structural layer structure. With a two-layer structure and when release is long, the third process is more adapted.

Frequency Tunable Microstrip Patch Antenna Using RF MEMS Technology

A novel reconfigurable microstrip patch antenna is presented that is monolithically integrated with RF microelectromechanical systems (MEMS) capacitors for tuning the resonant frequency. Reconfigurability of the operating frequency of the microstrip patch antenna is achieved by loading it with a coplanar waveguide (CPW) stub on which variable MEMS capacitors are placed periodically. MEMS capacitors are implemented with surface micromachining technology, where a 1-mum thick aluminum structural layer is placed on a glass substrate with a capacitive gap of 1.5 mum. MEMS capacitors are electrostatically actuated with a low tuning voltage in the range of 0-11.9 V. The antenna resonant frequency can continuously be shifted from 16.05 GHz down to 15.75 GHz as the actuation voltage is increased from 0 to 11.9 V. These measurement results are in good agreement with the simulation results obtained with Ansoft HFSS. The radiation pattern is not affected from the bias voltage. This is the first monolithic frequency tunable microstrip patch antenna where a CPW stub loaded with MEMS capacitors is used as a variable load operating at low dc voltages