Deepak Bansal

Design of vertical packaging technology for RF MEMS switch

Wafer-level micro-encapsulation is an innovative, low-cost, wafer-level packaging method for encapsulating RF MEMS switches. This article presents an approach for design and processing steps related to encapsulation of individual RF components e.g. CPW, RF MEMS switches, in view of the variation in performance subsequent to packaging. Bottom contact vertical packaging is more prone to misalignment margin and easy to make connections. Cavity height of 30 µm is optimized for bottom contact vertical packaging.

Comparative study of various release methods for gold surface micromachining

Abstract. A comparison of dry and wet release methods for surface micromachining of metallic structures, such as RF MEMS switches, test structures, bridges, and cantilevers is presented. The dry release process is optimized by varying the concentration of O2 and CF4 plasma and RF power. The plasma ashing of the sacrificial layer typically results in damage to metallic structures or stress-related deformation due to rise in temperature (>80°C). A wet release process using critical point drying (CPD) has been investigated to realize gold-electroplated structures with reduced residual stress. The CPD, being a low-temperature (31.1°C) process, is more suitable for compliant structures without any deformation.

Fabrication and analysis of radiofrequency MEMS series capacitive single-pole double-throw switch

Abstract. A compact radiofrequency (RF) MEMS single-pole double-throw (SPDT) switch based on series capacitive configuration is proposed. The critical process parameters are analyzed to improve the fabrication process. A technique of cold–hot thermal shock for lift-off method is explored. The residual stress in the structure is quantified by lancet test structures that come out to be 51 MPa. Effect of residual stress on actuation voltage is explored, which changes its value from 24 to 22 V. Resonance frequency and switching speed of the switch are 11 kHz and 44  μs, respectively, measured using laser Doppler vibrometer. Measured bandwidth of the SPDT switch is 20 GHz (5 to 25 GHz), which is verified with finite element method simulations in high frequency structure simulator© and an equivalent LCR circuit in advanced design system©. Insertion loss of the switch lies in −0.1 to −0.5  dB with isolation better than −20  dB for the above-mentioned bandwidth.

Design and fabrication of a reduced stiction radio frequency MEMS switch

Abstract. The design, fabrication, and mechanical characterization of a compact-reduced stiction see-saw radio frequency MEMS switch are presented. The switch has a resonance frequency of 9.8 kHz with a corresponding switching speed of 46  μs. Use of a floating metal layer and optimal contact area ensures reduced stiction and smaller capacitive leakage. Overall size of the switch is 0.535 (0.50×1.070)  mm2. Reduction in up-state capacitance also results in improvement in self-actuation voltage, insertion, and return loss. The optimized topology has improved the stiction and power handling of the switch.

Design and optimization of RF MEMS T-type switch for redundancy switch matrix applications

This paper presents a novel approach to monolithically implement a planar multiport radio-frequency (RF) microelectromechanical systems (MEMS) T-type switch. T-type switches are used as building blocks for redundancy switch matrix applications in space telecommunication. The T-type switch performs signal routing in three operational states. Two of them are turning states while the other one is a crossover state. The proposed design uses a series metal contact clamped-clamped beam SPST switches, four port cross junctions and a RF crossover. The simulated results for the entire T-type switch demonstrates an insertion loss of -0.46 dB, return loss of better than -15.50dB and isolation better than -17.73dB for all states for a wideband frequency range 0-30GHz. The switch gives excellent RF performance near X-band and Ku-band which is the most widely used frequency range for satellite communication.

Low temperature bonding techniques for MEMS devices

Conventional bonding techniques like fusion, glass frit, soldering, eutectic, and anodic bonding, have been used in packaging for micro-electro-mechanical systems (MEMS). These bonding techniques require high temperature which results in bending/buckling of MEMS devices especially in case of hanging structures. In this work, low temperature and low cost bonding techniques with commercially available epoxy 320 NC and photoresist SU-8 2010 are done. Bonding with commercially available epoxy 320 NC at room temperature leads to spreading of epoxy in device region and affects the device performance. To define bonding ring dimensions, photoresist SU 8 2010 is used as an adhesive. Sharp dimensions of SU 8 2010 bonding ring are achieved using lithography. Top silicon cap is fabricated using TMAH etching. The bonds made with these techniques gave good shear strength, as measured with an indigenous setup.

Silicon micromachined K-band filters

This paper describes a substrate integrated waveguide (SIW) based filter at K band frequency on silicon substrate. TMAH etching is used to form the via-holes for SIW cavities. Simulations and comparison of TMAH and Deep reactive ion etching (DRIE) etched cavity has been presented. A micro- machined filter is made from rectangular cavities integrated into a silicon substrate and is fed by coplanar waveguide (CPW) transmission-lines through current probes. Simulated filter using TMAH etching shows insertion loss of 0.29dB and return loss of 21.96 dB.

Design of MEMS based ‘cross over junction’ for T-type switch

This paper presents a novel design approach of T-type RF MEMS switch cross over junction, implemented using symmetric toggle switch (STS) as a basic building block. T-type switches are key elements for designing redundancy switch matrices. Proposed design is a dual type switch, i.e. under operation same bridge is used as an ohmic series switch as well as a capacitive shunt switch. This reconfigurable switch constitutes the cross over junction part for the T-type switch. Simulated results show an insertion loss of < 0.2 dB upto 10 Ghz and isolation is better than −20 dB over a band of 5 Ghz through capacitive path and is better than −80 dB up-to 10 Ghz through ohmic contact path. STS as a building block is used for designing cross over junction and is a technologically mature device. The designed actuation voltage of this cross over switch is 4.75 Volts and simulated resonant frequency is 3.253 KHz.

Low cost lift-off process optimization for MEMS applications

The patterning of thin films play major role in the performance of MEMS devices. The wet etching gives an isotropic profile and etch rate depends on the temperature, size of the microstructures and repetitive use of the solution. Even with the use of selective etchants, it significantly attacks the underlying layer. On the other side, dry etching is expensive process. In this paper, double layer of photoresist is optimized for lift-off process. Double layer lift-off technique offers process simplicity, low cost, over conventional single layer lift-off or bilayer lift-off with LOR. The problem of retention and flagging is resolved. The thickness of double coat photoresist is increased by 2.3 times to single coat photo resist.

Change of characteristic length with packaging for torsional MEMS switch

Fluid continuity theory is used to describe the dynamic response of open Micro-Electro-Mechanical-System (MEMS) devices. For a packaged device, at low pressure, the fluid continuity theory is no longer valid and a rarefication theory based on a Knudsen number is used. In an open MEMS device, the characteristic length which determines the Knudsen number is represented by the gap between the MEMS bridge and underneath actuation electrodes. On the other hand, for a packaged device, effective characteristic length is modified with the packaging cavity height. In this paper, for a packaged MEMS device, effective characteristic length with reference to the packaging height is derived.