Jinwen Zhang

CMOS-compatible micromachined edge-suspended spiral inductors with high Q-factors and self-resonance frequencies

This paper reports a new category of high-Q edge-suspended inductors (ESI) that are fabricated using CMOS-compatible micromachining techniques. This structure was designed based on the concept that the current was crowded at the edges of the conducting metal wires at high frequencies due to the proximity effect. The substrate coupling and loss can be effectively suppressed by removing the silicon around and underneath the edges of the signal lines. Different from the conventional air-suspended inductors that have the inductors built on membranes or totally suspended in the air, the edge-suspended structures have the silicon underneath the center of the metal lines as the strong mechanical supports. The ESIs are fabricated using a combination of deep dry etching and anisotropic wet etching techniques that are compatible with CMOS process. For a three-turn 4.5-nH inductor, a 70% increase (from 6.8 to 11.7) in maximum Q-factor and a 57% increase (from 9.1 to 14.3 GHz) in self-resonance frequency were obtained with a 11-/spl mu/m suspended edge in 25-/spl mu/m-wide lines.

Characterization and attenuation mechanism of CMOS-compatible micromachined edge-suspended coplanar waveguides on low-resistivity silicon substrate

This paper presents detailed characterization of a category of edge-suspended coplanar waveguides that were fabricated on low-resistivity silicon substrates using improved CMOS-compatible micromachining techniques. The edge-suspended structure is proposed to provide reduced substrate loss and strong mechanical support at the same time. It is revealed that, at radio or microwave frequencies, the electromagnetic waves are highly concentrated along the edges of the signal line. Removing the silicon underneath the edges of the signal line, along with the silicon between the signal and ground lines, can effectively reduce the substrate coupling and loss. The edge-suspended structure has been implemented by a combination of deep reactive ion etching and anisotropic wet etching. Compared to the conventional silicon-based coplanar waveguides, which show an insertion loss of 2.5dB/mm, the loss of edge-suspended coplanar waveguides with the same dimensions is reduced to as low as 0.5 dB/mm and a much reduced attenuation per wavelength (dB/lambdag) at 39 GHz. Most importantly, the edge-suspended coplanar waveguides feature strong mechanical support provided by the silicon remaining underneath the center of the signal line. The performance of the coplanar waveguides is evaluated by high-frequency measurement and full-wave electromagnetic (EM) simulation. In addition, the resistance, inductance, conductance, capacitance (RLGC) line parameters and the propagation constant of the coplanar waveguides (CPWs) were extracted and analyzed

A high-performance micro electret power generator based on microball bearings

In this paper, a high-performance micro electret power generator fabricated by simple bulk micromachining technology is presented. It has microballs as movable bearings for harvesting changing low-frequency vibration energy from the environment. The silicon V-grooves where the microballs slide have very smooth (1 1 1) planes, and so the device is sensitive to very slight vibration and almost has no resonant frequency. A plasma-enhanced chemical vapour deposition SiO2/Si3N4 double layer was used as the electret. The device was fabricated by simple micromachining technology suitable for mass production except for microball assembly. The influence of various frequencies and accelerations on the performance was studied in detail. The measurement results of this electret micro power generator show that the optimal load is proportional to the frequency, and inversely proportional to the acceleration. The peak-to-peak output charge and output power were 72 nC and 5.9 µW respectively at 20 Hz and 0.7 g with the optimal resistive load 626 kΩ. The work frequencies range from 100 Hz to a lower frequency (1 Hz). 112 nW can still be obtained in the minimum acceleration of 0.05 g at 10 Hz with the optimal resistive load, indicating that this device has high sensitivity. The possible application of our device in scavenging energy from low-frequency irregular movements, such as human motion, was proved by a primary experiment.

CMOS-compatible micromachining techniques for fabricating high-performance edge-suspended RF/microwave passive components on silicon substrates

This paper reports the micromachining techniques for fabricating edge-suspended RF/microwave passive components, which are proposed to deliver enhanced performance without sacrificing their mechanical strength and reliability. The fabrication incorporates ICP-DRIE dry etching and TMAH anisotropic etching techniques, which are both CMOS compatible. The edge-suspended structures were realized by a TMAH solution consisting of 5 wt% TMAH, 1.6 wt% Si and 0.5 wt% (NH4)2S2O8. This solution offers effective etching of silicon along the {100} and {110} planes, while having negligible etching on aluminum and {111} planes. The layout requirement for achieving edge-suspended passive components is also outlined on the basis of the analysis of the anisotropic etching along different crystal orientations. Using the techniques described here, high performance spiral inductors and coplanar waveguides (CPW) with significantly reduced loss are demonstrated. For a three-turn 4.5 nH inductor, a 70% increase (from 6.8 to 11.7) in maximum Q-factor and a 57% increase (from 9.1 GHz to 14.3 GHz) in self-resonance frequency are obtained with an 11 µm suspended edge in 25 µm wide lines compared to the conventional inductors without being micromachined. A 50 Ω edge-suspended CPW exhibits a reduction in insertion loss, from 2.4 dB mm−1 in a conventional CPW to 0.4 dB mm−1 at 39 GHz.

Design and fabrication of high performance wafer-level vacuum packaging based on glass-silicon-glass bonding techniques

In this paper, a high performance wafer-level vacuum packaging technology based on GSG triple-layer sealing structure for encapsulating large mass inertial MEMS devices fabricated by silicon-on-glass bulk micromachining technology is presented. Roughness controlling strategy of bonding surfaces was proposed and described in detail. Silicon substrate was thinned and polished by CMP after the first bonding with the glass substrate and was then bonded with the glass micro-cap. Zr thin film was embedded into the concave of the micro-cap by a shadow-mask technique. The glass substrate was thinned to about 100??m, wet etched through and metalized for realizing vertical feedthrough. During the fabrication, all patterning processes were operated carefully so as to reduce extrusive fragments to as little as possible. In addition, a high-performance micro-Pirani vacuum gauge was integrated into the package for monitoring the pressure and the leak rate further. The result shows that the pressure in the package is about 120 Pa and has no obvious change for more than one year indicating 10?13?stdcc s?1?leak rate.

A low-loss RF MEMS switch with dielectric layer on the lower surface of the bridge

This paper reports a low-loss RF MEMS switch with the dielectric layer on the lower surface of bridge instead of on the transmission line as conventional switches. Analysis on the fringing capacitance of switch capacitor shows this kind of switch has much smaller fringing capacitance and lower insertion loss than conventional one when the bridge is wider than transmission line. The simulation results obtained from 3D electromagnetic simulation tools well demonstrate the theoretical analysis. As increasing compact miniaturization and highly developed integration, this kind of switch with low insertion loss is expected a broad application in the future.

A simple micro pirani vasuum gauge fabricated by bulk micromachining technology

In this paper, a very simple micro vacuum pirani gauge made of single crystal silicon is presented. It was fabricated by standard bulk micromachining with only three masks. The high aspect ratio structure of the pirani gauge has large efficient gaseous heat transfer area, thus can increase the sensitivity of the pirani gauge. The dynamic range of the pirani gauge is 2Pa to 400Pa which should be larger if the power of the current source be larger with high sensitivity. And the average sensitivity is 184 K/W/Pa.

Design and simulation of 4-bit 10-14GHz RF MEMS tunable filter

This paper presents a 4-bit RF microelectromechanical system (MEMS) wide-band tunable filter at the 10–14GHz frequency range. Open-ended shunt stubs is utilized to load RF MEMS capacitive switches and MAM capacitors acting as the tunable cells, and leads to lower loss and more flexibility of design. The simulation results obtained by 3D electromagnetic simulation tool show that the tuning range is about 30% (from 10.5GHz to 13.5GHz) and the insertion loss is from −4.8dB to −5.2dB.

Microwave Performance Dependence of BST Thin Film Planar Interdigitated Varactors on Different substrates

This paper investigated the RF and microwave characterization dependence of BST (BaSrTiO₃) planar interdigitated (PID) varactors on different substrates, such as MO (MgO), LAO (LaAlO₃) and STO (SrTiO₃). Double-layer Ba_0.6Sr_0.4TiO₃/ Ba_0.4Sr_0.6TiO₃ thin film was deposited using reactive pulsed laser deposition (PLD) and then varactors were fabricated. The results show that the capacitance, tunability and Q-factor of the PID varactors are strong dependent upon the properties of the substrates. The capacitance of the PID varactor on STO is much higher than those on MO and LAO substrates, and so its self-resonant frequency is the lowest. The tunability of the PID varactors on MO, LAO and STO are 45%, 50% and 30% respectively at 40V DC bias. The Q-factors of three PID varactors on MO, LAO and STO are different, i.e., MO>STO>LAO.

Single-walled carbon nanotube film-silicon heterojunction radioisotope betavoltaic microbatteries

Ever since the appearance of nanomaterials and nanotechnologies, they have been used in almost every type of microbattery except for nuclear ones. Here we present a radioisotope betavoltaic (BV) microbattery based on a single-walled carbon nanotube (SWCNT) film that acts as a carrier separator. SWCNT film also provides a shortcut for carrier transportation. The energy conversion efficiency of a BV microbattery can reach up to 0.15% after the subtraction of the energy loss of beta particles in air and SWCNT film, proving that the SWCNT film-silicon heterojunction presents a promising configuration suitable for use in radioisotope BV microbatteries. Tracing the particle route, we achieved a charge collection rate of 59.9%, indicating that our device could potentially achieve higher performance. Primary strategies to improve the performance of the BV microbattery are discussed.