Chang-Auck Choi

A low-loss single-pole six-throw switch based on compact RF MEMS switches

A low-loss single-pole six-throw (SP6T) switch using very compact metal-contact RF microelectromechanical system (MEMS) series switches is presented. The metal-contact MEMS switch has an extremely compact active area of 0.4 mm /spl times/ 0.3 mm, thus permitting the formation of an SP6T MEMS switch into the RF switch with a total area of 1 mm/sup 2/. The MEMS switch shows an effective spring constant of 746 N/m and an actuation time of 8.0 /spl mu/s. It has an isolation loss from -64.4 to -30.6dB and an insertion loss of 0.08-0.19 dB at 0.5-20 GHz. Furthermore, in order to evaluate RF performances of the SP6T MEMS switch, as well as those of the single-pole single-throw RF MEMS series switch, we have performed small-signal modeling based on a parameter-extraction method. Accurate agreement between the measured and modeled RF performances demonstrates the validity of the small-signal model. The SP6T switch performed well with an isolation loss from -62.4 to -39.1dB and an insertion loss of 0.19-0.70 dB from dc to 6 GHz between the input port and each output port.

A self-aligned vertical comb-drive actuator on an SOI wafer for a 2D scanning micromirror

A self-aligned vertical comb-drive actuator for a two-axis tilt scanning micromirror is presented. Self-alignment between moving and fixed fingers is essential in order to avoid lateral instability leading to an in-plane rotational pull-in during an actuation. Multilayered masking films have been utilized to fabricate the self-aligned comb fingers. To generate high electrostatic torque, high-aspect ratio comb-drive actuators with 40 µm thick fingers have been realized on a silicon-on-insulator (SOI) wafer utilizing deep reactive ion etching (DRIE) technology. A delay-mask process (DMP) was employed in an etching step of a silicon device layer to assist etching of a buried oxide (BOX) layer at the bottom of narrow (5 µm) and deep (40 µm) silicon trenches. The DC mechanical scan angles of the actuators employed in the two-axis tilt, gimbal-configured micromirror were measured as ±2.1° at 48 V around an inner axis and ±1.8° at 44 V around an outer axis, respectively. The fabricated micromirror with a mirror area of 1 mm × 1 mm has mechanical resonant frequencies of 1.2 kHz around the inner axis (a mirror only) and 0.9 kHz around the outer axis (a frame and the mirror), respectively.

Micromachined air-gap structure MEMS acoustic sensor using reproducible high-speed lateral etching and CMP process

This paper presents a micromachined air-gap structure microelectromechanical systems (MEMS) acoustic sensor, which is fabricated via assisted high-speed lateral etching and chemical mechanical polishing (CMP). A sandwich structure (LTO/P2O5/LTO) as a sacrificial layer for the releasing process is proposed to produce an air-gap structure MEMS acoustic sensor. This sandwich structure can be etched selectively in a specific patterned P2O5 layer. In addition, the sandwich structure proved superior to using only low temperature oxide (LTO) layer for the releasing process. We confirmed that the proposed releasing method assisted by lateral etching and CMP is very effective for creating a clean air-gap cavity in MEMS devices. In this work, the air-gap structure MEMS acoustic sensor is based on the capacitance change of a movable thin poly-silicon membrane. A high-gain impedance converter was mounted on a printed circuit board (PCB) with a silicon MEMS acoustic sensor to transform the electrical signal for input acoustic pressure. The membrane size of the MEMS acoustic sensor was 1.5 × 1.5 mm2. The sensitivity achieved was about 0.018–5.17 mV Pa−1. The noise level of the fabricated device was 10 µV Pa−1.

A self-aligned vertical comb-drive actuator using surface micromachining for scanning micromirrors

A self-aligned vertical comb-drive actuator fabricated using surface micromachining is presented. One- and two-axis tilt scanning micromirrors with the actuators were fabricated and tested. A mechanical tilt angle of /spl plusmn/1.4/spl deg/ at 66 V/sub DC/ was achieved for a 1-mm-diameter micromirror.

Bistable planar polysilicon microactuator with shallow arch-shaped leaf springs

Bi-stable microactuators are necessary to implement optical switch and microrelay with low power and high reliability. In this work, we analyzed the buckling and vibration characteristics of a planar microactuators with shallow arch- shaped leaf springs. To investigate elastic stability of the proposed microactuator, we derived static buckling modes. A concentrated force of 0.35 muN at the center of beam was required for the snap-through motion for the beam length of 1600 micrometer, thickness of 3 micrometer, beam width of 6.5 micrometer and initial rise of 15 micrometer considering only the first buckling mode. We also analyzed vibration characteristics of arch-shaped leaf spring. The resonant frequencies of the first modes across over the second mode and keeps constant resonant frequencies over the cross point. On the contrary, the resonant frequencies of second modes become almost constant regardless of initial rise. The planar microactuator with shallow arch-shaped leaf springs at both sides were fabricated using silicon micromachining technology. The vertical structure of the planar microactuator features simplicity and consists of p-doped polysilicon as a structural layer and LTO (Low Temperature Oxide) as a sacrificial layer. The polysilicon was annealed for the relaxation of residual stress and HF GPE (gas-phase etching) process was finally employed in order to release the microactuators. These bi- stable planar microactuators with shallow arch-shaped leaf springs showed a high stiffness against external disturbance, and would be very useful for the stable operation of micro optical switch and microrelay.

Lateral field emission diode with wedge-type tip and nanogap on separation by implantation of oxygen silicon

A field emission diode array with a novel nanometer scale silicon gap in a separation by implantation oxygen structure was fabricated using the thin film stress that had been generated during high-temperature annealing and cooling. In this work, an interelectrode gap ranging from 20 to 100 nm was obtained depending on the width of the pattern when the patterned wafer was cooled after annealing at 1050 °C for 1 h in N2 ambient. The parameters for determining the gap size were identified, and the crystal orientation dependency in forming the gaps was clarified. The proposed nanogap formation technique is very simple and applicable to a field emission (FEA) with a short interelectrode distance. The fabricated FEA exhibited a turn on voltage of 25 V and an emission current of 6 μA per tip at 35 V.

Field activated lateral-type polysilicon emitter with extremely high emission current and very low turn-on voltage

A lateral-type poly-Si field emission device was fabricated by utilizing the local oxidation of silicon (LOCOS) process and a simple and efficient activation technique of the tip end was proposed to achieve a high emission current. The fabricated single field emitter exhibits excellent electrical characteristics such as a very low turn-on voltage of 2 V and an extremely high current of ∼500 μA at anode to cathode voltage of 30 V. These superior field emission characteristics are believed to be due to both an increased enhancement factor (β) by appropriate activation and originally sharpened tip by the LOCOS process.

Sensing gap reconfigurable capacitive type MEMS accelerometer

A novel sensing gap reconfigurable capacitive type MEMS accelerometer with high sensitivity and high resolution is designed, fabricated and characterized. The present MEMS accelerometer is fabricated by using simple SOI process-DRIE. However, conventional Silicon on Insulator (SOI) process is hard to make patterns which is smaller than 1 um because of its high aspect ratio and ICP etching error such as loading-effect and under-cutting. So we have adopted a simple idea of the MEMS actuator-stopper system to modulate the sensing gap precisely. Unlike previous capacitive type MEMS accelerometer which has an anchored reference comb electrodes, the proposed accelerometer has a movable reference comb with MEMS electrostatic actuators and stoppers. By simply applying DC bias to MEMS actuators, the reference comb electrode is moved to the sensing comb structure until the actuators contacting the stoppers. The gap between sensing comb fingers and reference comb fingers is reduced by the gap between actuators and stoppers. In this paper, the initial sensing gap is 1.5um and it reduced to 0.5um, when working. Then, the overall capacitance and sensitivity is simple increased. The capacitance is increased from 3.47pF at the OFF state to 5.35pF at the ON state by applying 2V DC bias.

A single-pole 6-throw (SP6T) antenna switch using metal-contact RF MEMS switches for multi-band applications

A single-pole 6-throw (SP6T) antenna switch using metal-contact RF micro-electro-mechanical system (MEMS) series switches has been developed for multi-band applications. The fabricated metal-contact MEMS switch with a broad signal line gap of 140 /spl mu/m shows a very high isolation loss of -51 dB at 2 GHz because its center-wedge (CW) can control a membrane stiction problem due to the anchor role. The pull-down voltage (V/sub P/) of the MEMS switch is 27.5 V and its leakage current is 26.1 /spl mu/A at V/sub P/. The SP6T antenna switch, which has six SPST MEMS switches, is comprised of two transmitter (Tx) ports and four receiver (Rx) ports for quad-band application. The chip area is very compact to 1 mm/sup 2/ (1.3 mm /spl times/ 0.8 mm). This antenna switch has an isolation loss of -48 dB and an insertion loss of -0.27 dB at 2 GHz between the antenna (ANT) port and transmitter portl (T/spl times/1) at V/sub A/ = 36V.

The Fabrication of an Applicative Device for Trench Width and Depth Using Inductively Coupled Plasma and the Bulk Silicon Etching Process

Copyright 2014 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2014.15.1.49 TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS Vol. 15, No. 1, pp. 49-54, February 25, 2014