Kamaljit Rangra

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.

A novel interdigitated, inductively tuned, capacitive shunt RF — MEMS switch for X and K bands applications

This paper presents a new type of capacitive shunt RF-MEMS switch. In the proposed design, interdigitation of signal lines with actuation electrodes is used to make a compact device. A bridge structure anchored in between ground planes and attached to two cantilevers on either side has been used to implement the switch structure. This novel structure is used to inductively tune the isolation peaks in X and K bands which is not possible with conventional approach. The designed switch shows an insertion loss of 0.01 dB to 0.11 dB over the frequency range from 1 to 25 GHz. Isolation of 34.71, 34.33, and 40.7 dB has been observed at 10.4 GHz, 11 GHz and 21.4 GHz when bridge is electro-statically actuated with either left, right or both cantilevers in the down state respectively. The bridge structure shows a pull-in voltage of 12.25 V and switching time of 34.40 μs whereas left and right cantilevers have 7.5 V and 57 μs. The designed device can be useful for the future multiband communication applications.

Resist debris formation in electron beam lithography

Abstract The resist debris (RD) formation dependence on beam stepping to beam size ratio in electron beam lithography (EBL) is theoretically and experimentally investigated. The theoretically simulated results show a distinct variation in RD formation as the beam stepping to beam size ratio is varied from 0.5 to 2.0. The corresponding experimental results show a very close resemblance with the simulated results. It is further demonstrated that this undesirable phenomenon of RD formation gives another dimension to look at the problem of proximity exposure effect in EBL and can also be well utilized in certain cases.

Proximity exposure compensation and resist debris formation in electron beam lithography

A theoretical and experimental investigation into the formation of resist debris due to proximity exposure compensation (PEC) in electron beam lithography is provided. The two dimensional simulation of resist contours in closely spaced rectangular patterns shows that the unsupported resist fragments (debris) originate at the top of the resist when a PEC scheme based on dose variation method is used to compensate for the proximity exposure effects within and between the patterns. It is found that by taking some precautions during electron exposure and development process, the adverse effects of resist fragments can be eliminated.

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.

On-wafer electro-mechanical characterization of silicon MEMS switches

The feasibility of integrating the RF MEMS switches in space and wireless communication systems has generated tremendous interest in related design, fabrication and characterization methodologies. The space applications make long term reliability of the devices a very pertinent issue and involves both the process and device characterization. In this paper we describe the experimental setup and measurement results on RF MEMS switches fabricated for DC to 30 GHz applications. The on-wafer experimental setup, based on standard manual microprobe station provides dual pulse actuation voltage waveforms with programmable period and amplitude, ranging from 10/sup -5/ to 1 sec and 0-200 volts respectively. The usefulness of the dual-pulse testing is demonstrated by the minimal charge generation in the dielectric layer and capacitance measurements with negligible variations over long measurement periods.

Online exposure dose correction during electron beam pattern delineation by blanking width modulation

Abstract The electron beam exposure over extended periods of time using guassion electron beam in a SEM like column is highly prone to variation in exposure dose due to changes in the incident beam current, charging on the resist surface etc. This leads to the loss of global linewidth control. This paper presents a method in which the exposure current is monitored in-situ and the required correction to the exposure time is provided automatically in order to maintain uniform exposure globally.

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.