Kaihsiang Yen

Applied electrostatic parallelogram actuators for microwave switches using the standard CMOS process

This paper presents the fabrication of a laminated-suspension microwave switch using a conventional 0.6 µm single polysilicon three metals complementary metal-oxide semiconductor process. The post-processing is completed with maskless dry etching. The micromachined microwave switch consists of two electrostatic parallelogram actuators, two T-type connectors and one coplanar waveguide on a p-type silicon substrate. The switch only requires a low dc voltage of around 18 V for electrostatic traction. The testing results of the microwave switch show that the insertion loss is 6.8 dB and isolation is -7.8 dB in the range 10-20 GHz. In addition to demonstrating the design and fabrication of the microwave switch, this paper summarizes the experimental results.

A wideband electrostatic microwave switch fabricated by surface micromachining

Abstract An electrostatic microwave switch has been implemented by applying surface micromachining processes. The substrate of the microwave switch is gallium arsenide (GaAs). The structure of the microwave switch contains a gold coplanar waveguide and a suspended aluminum membrane. The Al membrane is directly anchored to the sidewalls of the GaAs substrate. All processing temperatures are under 350°C. The microwave switch operation is controlled by electrostatic force. The experimental results of the microwave switch show a microwave isolation of ‐40 dB and an insertion loss of ‐0.5 dB in the range of 0.1 to 7 GHz. In addition to demonstrating the design and fabrication of the microwave switch, this work summarizes experimental results.

High aspect-ratio fine-line metallization

This study is aimed at making metallic fine lines characterized with high aspect ratio. There are two methods we have developed. One is the trilevel lift-off method with submicron lithography, and the other is the lift-off method by using the commercial negative photoresist SU-8 made by IBM. First, the trilevel lift-off method is described. A pre- imidized, soluble polyimide layer of OCG Probimide 293 A is spun on a wafer with thickness 4 micrometer. A 120 nm thick layer of silicon oxynitride was formed on the polyimide by PECVD. A layer photoresist layer was applied and patterned. This photoresist layer is used as the etching mask of silicon oxynitride by RIE with the gas CF4 plasma. Similarly, the silicon oxynitride is used as the etching mask of the thick polyimide layers by RIE with the gas O2 plasma. After metallization the pre-imidized polyimide is dissolved in methylene chloride lifting off the oxynitride and metal layers. Following this way, the submicron lithography, such as silylation technology, is suitable to make the aspect ratio up to 10 and the metal line will still have 3 micrometer height. The other is the lift-off method by using negative photoresist SU-8. This SU-8 is originally used as high aspect ratio molding. The linewidth of SU-8 is reduced to 2 micrometer linewidth with 12 micrometer height, and used as the remover to lift off after metallization. This SU-8 makes the fine-line metallization of 2 micrometer linewidth to achieve the aspect- ratio up to 5.

Fabrication of the planar angular rotator using the CMOS process

This investigation proposes a novel planar angular rotator fabricated by the conventional CMOS process. Following the 0.6 /spl mu/m SPTM (single poly triple metal) CMOS process, the device is completed by a simple post-process with maskless etching. The suspension unit rotates around its geometric center with electrostatic actuation. In addition to having a single rotatory component, 2/spl times/2 and 3/spl times/3 arrayed components are designed to have a larger rotatory angle with less actuation distance. The proposed design adopts an intelligent mechanism, including slider-crank and four-bar linkage, to permit simultaneous motion. With driving voltages of around 40 volts, the CMOS planar angular rotator could be driven. Comparing to the most common planar angular, micromotor, the design proposed herein has a shorter response time and longer life without the problems of friction and wear.

Wideband microwave switch by micromachining techniques

A micromachined microwave switch has been made on a semi- insulating GaAs substrate using a suspended membrane, gold coplanar waveguide (CPW), and electrostatic actuation as the switching mechanism. The electrostatic traction comes from the dc voltage applied between the ground of the CPW and the suspended membrane.

Real-time monitoring of thickness of silicon membrane during wet etching using a novel surface acoustic wave sensor

This study presents a novel method based on the surface acoustic wave (SAW) sensor, for monitoring the thickness of a silicon membrane in real time during wet etching. Similar to accelerometers and pressure sensors, some micro-electro-mechanical systems (MEMS) devices require the thickness of silicon membranes to be known precisely. Precisely controlling the thickness of a silicon membrane during wet etching is important, because the thickness strongly affects post-processing and device performance. Moreover, the proposed surface acoustic wave sensor allows the thickness of a silicon membrane to be monitored from a few μm to hundreds of μm in situ, which depends on the periodicity of interdigital transducers (IDT). A novel method, which differs from any in previous work on etch-stop techniques, is developed in-situ for monitoring the thickness of a silicon membrane during wet etching. In summary, the proposed method for measuring the thickness of a silicon membrane in real time, is highly accurate; is simple to implement, and can be mass-produced. This work also describes the principles of the method used, detailed process flows, the method of taking measurements and the simulated and experimental results. The theoretical and measured values differ by an error of less than 2.50μm, so the results closely agree with each other.

In-situ monitoring of thickness of quartz membrane during batch chemical etching using a novel micromachined acoustic wave sensor

This work presents a novel method based on the surface acoustic wave (SAW) device for monitoring in-situ the thickness of quartz membrane during batch chemical etching. Similar to oscillators and resonators, some SAW devices require the thickness of quartz membranes to be known precisely. Precisely controlling the thickness of a quartz membrane during batch chemical etching is important, because it strongly influences post-processing and frequency control. Furthermore, the proposed micromachined acoustic wave sensor, allows the thickness of a quartz membrane from a few /spl mu/m to hundreds of /spl mu/m to be monitored in-situ. In particular, the proposed method is highly appropriate for monitoring in-situ a few /spl mu/m thick quartz membranes, because the thickness of a quartz membrane is proportional to the phase velocity. In summary, the proposed method for measuring the thickness of quartz membrane in real time, has high accuracy, is simple to set up and can be mass produced. Also described herein are the principles of the method used, the detailed process flows, the measurement set-up and the simulation and experimental results. The theoretical and measured values differ by an error of less than 2 /spl mu/m, so the results agreed with each other closely.

Fabrication of diffractive optical elements using the CMOS process

This investigation presents a novel type of DOEs fabricated by the conventional CMOS process. A simple post-CMOS process is applied to form the relief pattern, which can be used directly for its optical properties or serve as a mold for the subsequent replication. By using the CMOS process, in addition to reducing the depth, alignment, dimension, and shape errors of the pattern, the scale is minimized by the advancing microfabrication as well. The performance of arbitrary DOEs can be directly related to the diffraction efficiency of the gratings. Therefore, in this investigation, the shape of the multi-level gratings is designed and the diffraction efficiency is calculated by the rigorous vector coupled-wave analysis. The largest constraint of the CMOS process for the multilevel gratings is that the depth of each layer is different and unchangeable. However, a suitable length for each level can be determined and, in doing so, the diffraction efficiency can reach 81%.

Integrated eyeball-tracking device

This investigation presents a concept of integrated device, which tracks the movement of eyeball in real time. Integrated optical components are applied to perform infrared oculography to find the position of the eyeball. First, the photodiodes emits infrared to human eyes via the output coupler, then the reflected light is collected by the input coupler and detected by the photodetectors. By analyzing the electrical signal, we could figure the position of the eyeball out. The basic principle is based on the differential of reflected index between sclera and iris. The light source and detectors are settled on the side of goggles worn and, in doing so, the eyesight could be wide without obstacles. Therefore, the optical guiding interconnection is an essential issue for the eyeball- tracking device. Since the fine line gratings are necessary for the optical coupler, the electron beam writing is used to meet the requirement. The gratings with 40 nm line width are achieved, and it is sufficient for optical coupling. On the other hand, the electrical signal related eyeball position is simulated. We could translate the electrical signal readout into the coordinate of the eyeball position. The whole eyeball-tracking device would be small volume, less weight, and portable.

Fabrication of a micromachined optical modulator using the CMOS process

This investigation presenst a micromachined optical modulator with electrostatic actuation fabricated by the conventional CMOS process. The modulator is operated by interaction of fixed part, stationary gratings, and movable part, sliding gratings. The period of the gratings varies with the slide of the movable part, thereby allowing different diffraction patterns of the reflected light. In addition, 100% modulation in the first order can serve as an optical switch. All procedures following the CMOS process merely require a simple post-process. With maskless etching, the micromachined optical modulator is developed to obtain a high-aspect-ratio structure and high efficiency of modulation. Compare to the commercially available acoustic ones, the micromachined optical modulator proposed herein is smaller and weigh less.