Winston Sun

Bistable nanowire for micromechanical memory

We present a micromechanical device designed to be used as a non-volatile mechanical memory. The structure is composed of a suspended slender nanowire (width: 100 nm, thickness: 430 nm, length: 8 to 30 ?m) clamped at both ends. Electrodes are placed on each side of the nanowire to (1) actuate the structure during the data writing and erasing mode and (2) determine its position by measuring the capacitive bridge in the reading mode. The structure is patterned by electron beam lithography on a pre-stressed thermally grown silicon dioxide layer. When later released by plasma etching, the stressed material relaxes and the beam buckles by itself to a position of lower energy. These symmetric bistable Euler beams exhibit two stable deformed. This paper presents the microfabrication process and analysis of the static buckling of nanowires. Snapping of these nanowires from one stable position to another by mechanical or electrical means will also be discussed.

A Ku-band Dual-SPDT RF-MEMS Switch by Double-Side SOI Bulk Micromachining

This paper presents the design, fabrication method, and measurement results of a low-loss ohmic-contact radio-frequency microelectromechanical systems (MEMS) switch. A novel bidirectional electrostatic actuation mechanism has been developed for a dual single-pole double-throw switch that could be used for an X-Ku-band low-temperature cofired ceramic switched-line-type phase shifter. A high-aspect-ratio deep reactive-ion etching process and a thick gold-plating process were used to develop low-insertion-loss air-suspended MEMS waveguides and low resistive ohmic contacts. A typical insertion loss of 0.56 dB, a return loss of 19.4 dB, and an isolation of 51.4 dB were obtained at a Ku-band frequency of 12 GHz.

rf microelectromechanical system device with a lateral field-emission detectora)

We propose a micromachined device that utilizes the field-emission (FE) phenomenon as a mean to modulate signal for radio-frequency microelectromechanical system applications. In this article, we present the stationary reference (SR) device and the resonator-embedded (RE) device and compare their field-emission performances. The SR device contains no moving part and is used to examine the conditions to excite field emission. The RE device has an embedded microresonator of bandpass filter characteristic. Due to enhanced tip sharpness and closer gap, initial results show that compared to the SR device, the FE current of the RE device has been increased by 192 times under the same anode-cathode potential difference of 240V and 2×10−8Torr vacuum level.

A 12-GHz DPDT RF-MEMS Switch with Layer-Wise Waveguide/Actuator Design Technique

A novel design of double-pole double-throw (DPDT) RF-MEMS switch for 12-GHz phase shifter has been developed to minimize the electrical crosstalk between the signal waveguide and electrostatic actuator by allocating them in separate layers of an SOI wafer. Compared with the previous other reports, our design can use relatively large area on the chip to accommodate more electrostatic actuator and to have more electrical ground planes. With this newly developed method, silicon RF-MEMS devices will be able to overcome the drawback of solid-state devices in terms of performance, device size, and cost. This paper reports driving voltage of 4V with the switching speed of 12 microseconds, insertion loss of 3 dB, return loss of 12 dB, isolation of 30dB at 12 GHz.

In-plane bistable nanowire for memory devices

We present a micromechanical device designed to be used as a non-volatile mechanical memory. The structure is composed of a suspended slender nanowire (width: 100 nm, thickness: 430 nm, length: 8 to 30 mum) clamped at both ends. Electrodes are placed on each side of the nanowire to 1) actuate the structure during the data writing and erasing mode and 2) determine its position by measuring the capacitive bridge in the reading mode. The structure is patterned by electron beam lithography on a pre-stressed thermally grown silicon dioxide layer. When later released by plasma etching, the stressed material relaxes and the beam buckles by itself to a position of lower energy. These symmetric bistable Euler beams exhibit two stable deformed. This paper presents the microfabrication process and the analysis of the static buckling of nanowires. Snapping of these nanowires from one stable position to another by mechanical or electrical means will also be discussed.

A foundry fabricated high-speed rotation sensor using off-chip RF wireless signal transmission

A novel MEMS surface-micromachined non-contact high-speed rotation sensor with total surface area under 4 mm/sup 2/ was developed using the MCNC Multi-User MEMS Processes (MUMPs). This paper reports the initial characterization of the sensor, including rotation and vibration tests. Initial results indicate that this piezoresistive sensor is capable of wirelessly measuring rotation speeds at /spl sim/2Hz/rpm/V with 5V input in the 100 to 6000 rpm rotation range. We believe our groundwork will allow the MEMS community to use the MUMPs foundry service to design simple and reliable high-speed rotation sensors that can be interfaced with commercial wireless chips for signal transmission.

Design, Simulation, Fabrication, and Characterization of a Digital Variable Optical Attenuator

In this paper, we present the design, simulation, fabrication, and some measurement and characterization of a novel 16-bit digital variable optical attenuator (VOA) that attenuates by switching individual mirror of an array as an attempt to achieve input voltage variation independence and output linearization. The design was aided by a simulation package that features coupled electrostatic and mechanical solver. The mirror array spans an area of 1500times1500 mum2 and contains 16 equal-length rectangular micromirrors. Each mirror is suspended by two torsion beams. Experiments on beam design and width variations are conducted. Assuming Gaussian distribution, the mirror widths computed by an iteration algorithm vary from about 40 to 250 mum. Based on silicon-on-insulator (SOI) technology, two fabrication schemes to open the backside optical entrance were investigated. A hydrofluoric (HF) acid vapor-phase-etching (VPE) setup built to release the microstructure anhydrously is the key to achieve high yield especially for fragile components. Surface flatness, resonance frequencies, and tilt angles of selected mirrors were characterized. Quartz chips patterned with aluminum electrodes and 10 mum-high SU8 spacer columns were fabricated and assembled to corresponding device chips. Optical performance adversely affected by mirror bending is believed to originate from the intrinsic stress of the SOI wafer

An SOI bulk-micromachined dual SPDT RF-MEMS switch by layer-wise separation design of waveguide and switching mechanism

A compact monolithic RF-MEMS switch (2mm × 4mm in area) with the dual single-pole-double-throw (SPDT) configuration was developed by using the SOI bulk micromachining technique. The electrostatic comb-drive actuators and the mechanically movable coplanar waveguides were implemented on the low-resistive active SOI layer and the high-resistive handle layer, respectively, to effectively allocate the device footprint. Electrical crosstalk between the waveguide and the electrostatic actuator was suppressed by using the buried silicon dioxide layer. At a driving voltage of 35V, the switch exhibits an insertion loss of 3dB and isolation of 30dB at 12GHz.

Development of a Dual-SPDT RF-MEMS switch for Ku-band

This paper presents the design, fabrication method and measurement results on a low-loss Ohmic-contact RF-MEMS switch with a bi-lateral actuation for a Dual-SPDT switching system. The switch was fabricated based on the silicon bulk-micromachining technology and a layer-wise technique on an SOI wafer. We demonstrated a compatibility with electroplating and high aspect-ratio Deep-RIE process to have loss-less quasi-air-suspended MEMS waveguides and adequately thick gold layer for side-wall ohmic contact. Typical performance shows 0.56 dB insertion loss, 19.4 dB return loss and 51.4 dB isolation at the Ku-band frequency of 12 GHz.

Design and simulation of a 16-bit variable optical attenuator

Presents an initial design and simulation results of 16-bit variable optical attenuator (VOA) with chip dimensions of 4 /spl times/ 4 /spl mu/m/sup 2/. Initial results indicate device-switching time is below 1 ms at a driving voltage of above 100 V. VOAs are widely used in optical communication and signal processing systems to attenuate light intensity between input and output optical ports. This VOA is currently under development and will be fabricated using SOI technology.