Papers by Keyword: Bulk Micromachining

Abstract: The ProTEX^® PSB thin film as a photosensitive layer has been released in the market as an alternative replacement for silicon nitride or silicon oxide wet etch masks. In this work, this film has been deposited on SiC-on-Si wafer for the back-etching of the bulk Si to leave SiC thin film to be used as a pressure sensor diaphragm. This paper will discuss the process flow to estimate the optimized ProTEX^® PSB thin film thickness for the sufficient back-etching of the 300um bulk Si. This thickness is defined by the following parameters: spin-coating rotational speed, final cure temperature and hard bake time of coating. Several samples of ProTEX^® PSB thin films have been preliminary characterized by infinite focus microscopy (IFM) and scanning electron microscopy (SEM) to examine the substrate surface conditions and the effects of undercut edges structure. Based on these data, it was determined that the optimum thickness of ProTEX^® PSB for this project is 2.133 μm with the spin speed of 3000 rpm, the first bake temperature of 110 °C in 120 seconds and the second bake temperature of 240 °C in 60 seconds. We conclude that ProTEX^® PSB can withstand the etch mask with etch rate of 1.28 μm/min for 8 hours and gives good quality effect of undercut edge on the SiC-on-Si wafer.

Abstract: The monolithic integrated technology of MEMS was discussed. First discussed the advantages and difficulties faced by the MEMS monolithic integration technology. Second the features and the process of the mainstream MEMS monolithic integration technology was introduced. And finally put forward a SOI MEMS monolithic integration technology, the technology with no high-temperature process, Post-CMOS integrated solution, compatible with the CMOS process. This technology can achieve high aspect ratio, high-performance micro-inertial devices..

Abstract: A low powered hydrogen gas sensor of the FET (field-effect transistor) structure was designed, fabricated and characterized for self-compensation to outer environments. The dual-gate FET hydrogen sensor was integrated with a micro-heater and two Pt-gate FETs; a sensing device for hydrogen detection, and a reference device as an electrical compensator. The identical output between the sensitive-FET and reference-FET was stable at temperatures ranging from room temperature to 250°C due to the same temperature dependence of the currentvoltage (IV) characteristics. The Pt-FET sensor showed stable responses to hydrogen at a range of operation temperatures. The optimal point in the micro-heater operation for 5,000 ppm H₂ gas injection was approximately 150°C. The highest sensitivity was 0.112 mA, and the response and recovery times were 18 sec and 19 sec, respectively. The low-power MOSFET gas sensor was found to be suitable for applications in portable gas monitoring units and automobiles.

Abstract: In the present work we report design, simulation, fabrication and characterization of thin film bulk acoustic resonator (FBAR). The FBAR has been modeled as a single port device with two terminals. The FBAR has been fabricated using Si-SiO₂-Al–ZnO-Al structure. Zinc Oxide (ZnO) films were deposited by RF magnetron sputtering using Ceramic ZnO target in Ar-O₂ (1:1) ambient without external substrate heating. The XRD result confirms the preferred C-axis orientation of the films required for good piezoelectric properties. These ZnO films have been used to fabricate air gap type resonator. A four mask process sequence was used for this purpose. Lift-off process was used to pattern Al top electrode. In order to create the air cavity under the active device area, the bulk Si was etched in 40 % KOH at 80 °C. A specially designed mechanical jig was used to protect the front side of the device during anisotropic etching. Vector network analyzer was used to measure the reflection coefficient (S₁₁: Return Loss) of the device. The resonant frequency of the resonator was measured to be 2.89 GHz as compare to the simulated frequency of 2.85 GHz with a return loss of 14.51 dB.

Abstract: The advantages of micromachining over conventional fabrication include precise dimensional control, integration of on-chip circuits and potential low cost owning to batch processing. Fabrication microspeaker for hearing instrument application using MEMS technology is challenging because of certain critical requirements, including their small size, low driving voltage, high output sound pressure level, flat frequency response and low energy consumption. A small in size, lightweight, and low cost microspeaker is demanded for application such as cellular phones and hearing aids. The device consist of two part; first parts is a micromachined polyimide membrane as the sound generating plate, where thevoice coil placed on the top of membrane, and the coil is a single loop voice coil. The second part is back plate permanent magnet. The disc permanent magnet bonded on acoustic hole plate is Neodymium-Iron-Boron (NdFeB) with magnetization of 1.45 T, diameter 1.6 mm, and thickness 0.8 mm. The fabrication process and performance of the first result device is discussed, and the thickness of electroplated single loop voice coil copper 10 mm and acoustic hole bonded together. The total size of the microspeaker chip is 5 mm x 5 mm x 1.5 mm, polyimide membrane thickness 2 mm.

Abstract: Much of the recent ongoing advanced research into the quest for improved etching techniques has brought forth a broad concept for the fabrication of micro/nano-electromechanical systems (MEMS/NEMS) having high accuracy, precision, efficiency, compatibility and through-put of metallic- as well as carbon-composition structural phases. This in turn leads towards a thorough understanding of the sensing, trapping, separating, controlling, positioning, directing, concentrating and manipulating of micro-nano-sized particles - predominantly biological particles - in the emerging MEMS/NEMS technological field. This paper focuses its attention on the easiest means of wet-etching {100}-type silicon wafer surfaces by guiding the choice of [<100> or <010>] orientation (at 45° to the normal orientation). This anisotropic etching is performed in KOH solution. Here, consideration is not concerned to a large extent with process parameters as in anodic oxidation, an intensely doped boron etching stops and silicon wafer surface back-etching. The main concern of the present practical application route involves a passivating material (silicon dioxide, SiO2) and two masking stages (for a two-step etching process). As a example of this method, silicon cantilever beams having vertical edges are produced. It is concluded that the method presented will be helpful in the comprehensive study of resonators, pressure/temperature sensors, three-dimensional carbon micro-electrodes, actuators and accelerometers for bioparticle applications.

Abstract: In the world of MEMS processing today, fabrications of membrane are performed using bulk micromachining (BMM). However these techniques not easiest to integrate with CMOS standard process due to not compatible of the processing flow. An attractive alternative deployment of surface micromachining (SMM). There is a trend to use surface micromachining to their advantage of simplicity in design and fabrication process compatibility. This paper presents process development of thin layer membrane for very low capacitive pressure sensor application. The structure of the membrane consists of parallel plate which both top and bottom electrodes were fixed at both sides. Utilizing CMOS MEMS process compatible fabrication of the thin layer membrane involved in three stages; i) hole opening etch, ii) sacrificial intermediate oxide release etch and iii) closing of etch holes. Therefore seals-off process characterization and optimization experiment are presented in this paper, will spur advancement in the development of a CMOS MEMS product for very low capacitive pressure sensor.

Abstract: High aspect ratio silicon carbide (SiC) microstructures are needed for microengines and other harsh environment micro-electro-mechanical systems (MEMS). Previously, deep reactive ion etching (DRIE) of low aspect ratio (AR ≤1) deep (>100 *m) trenches in SiC has been reported. However, existing DRIE processes for SiC are not well-suited for definition of high aspect ratio features because such simple etch-only processes provide insufficient control over sidewall roughness and slope. Therefore, we have investigated the use of a time-multiplexed etch-passivate (TMEP) process, which alternates etching with polymer passivation of the etch sidewalls. An optimized TMEP process was used to etch high aspect ratio (AR up to 13) deep (>100 *m) trenches in 6H-SiC. Power MEMS structures (micro turbine blades) in 6H-SiC were also fabricated.

Abstract: In this paper, presented are the design and the fabrication of the novel bulk-micromachined gyroscope with its detection and control circuit. The proposed structure is designed to have good properties such as heavy proof mass, a large movement and high moving velocity of the proof mass at an operating frequency. Despite of an appropriate design of the proof mass and comb electrodes, the high-Q property and the capacitance measurement scheme inevitably bring on nonlinear property and limited bandwidth of the system. Moreover, temperature variation degrades the stability of the performance. In this paper, we adopt a feedback control scheme to achieve a linear output and a less sensitive operation to the temperature variation. Through experiments, it is confirmed that the designed gyroscope and the control circuit achieve performances of wide input range of 1,000 deg/sec and bandwidth of 80 Hz.