N. Hoivik

Digitally controllable variable high-Q MEMS capacitor for RF applications

This paper describes the novel design of an electrostatic digitally controllable variable MEMS capacitor constructed using Cronos MUMPS technology and flip-chip technology processing. The capacitor consists of an array of individual plates of equal area, which are connected to the bonding pads by springs of varying width. This creates a cascading snap-down effect when actuated by electrostatic forces. The capacitor has a measured Q-factor of 140 at 750 MHz, and a tuning ratio of 4:1.

Atomic layer deposition of conformal dielectric and protective coatings for released micro-electromechanical devices

This paper describes a novel fabrication approach using Atomic Layer Deposition (ALD) of dielectric materials to protect and coat released MEMS devices. The nature of ALD film ensures coverage on all sides of a released MEMS device and is done at a relatively low temperature (down to 150/spl deg/C). The ALD film thickness can be precisely controlled as each reaction cycle deposits approximately one monolayer of atoms. To demonstrate the concept of conformal layer deposition, alumina (Al/sub 2/O/sub 3/) was deposited onto released MEMS devices prior to electrostatic testing. Curvature and increase in beam stiffness for coated MEMS devices were investigated.

Atomic layer deposition (ALD) technology for reliable RF MEMS

A nano-layer inorganic coating technology has been developed to protect RF MEMS from electrical shorting as well as long-term reliability failures due to charging or moisture. The combination of alumina dielectric and zinc-oxide conducting layers can be constructed one atomic layer at a time. At 177/spl deg/C, the released RF MEMS devices can be coated on a wafer or as a single device with conformal, inorganic coverage where the thickness and electrical conductivity can be controlled to meet desired values. With additional chemical treatment, the surface could be made hydrophobic to avoid moisture-induced stiction. The long-term reliability problem is the main barrier that impedes the growth of RF MEMS applications. This novel atomic layer deposition (ALD) technology can help in overcoming this limitation.

Flip-Chip-Assembled Air-Suspended Inductors

This paper discusses high-performance planar suspended inductors for hybrid integration with microwave circuits. The inductors are fabricated using a silicon surface micromachining foundry process and assembled using flip-chip bonding. The silicon substrate is removed, leaving a metal inductor suspended 60 mum above the microwave substrate, thus reducing the parasitic capacitance and loss. Various rectangular, octagonal, and circular inductor geometries with one to five windings are designed with inductance values between 0.65 and 16 nH to demonstrate the flexibility of this technique. Measured self-resonant frequencies are between 5 and 34.8 GHz, with quality factors from 45 to 100. Equivalent circuits extracted from measurement for each inductor type show good agreement with measured impedance and full-wave simulations over frequency. The dc current handling limit is 200 mA

Atomic layer deposition of Al/sub 2/O/sub 3//ZnO nano-scale films for gold RF MEMS

Atomic layer deposition (ALD) was used to create an Al/sub 2/O/sub 3//ZnO thin film for gold capacitive RF MEMS switches. These films exhibited a widely tunable range of physical properties, allowing the creation of a material capable of dissipating trapped charges and maximizing the on-capacitance of the switch. Predicted pull-down voltages of the ALD-coated switches underestimated the experimental findings due to residual stresses in the ALD film and annealing of the gold during the ALD deposition. Switch cycles to failure were measured using a 10 dBm, 10 GHz, CW signal with a bipolar actuation voltage of 25-55 V. Preliminary testing showed lifetimes of 400 million cycles using 50/50 ALD Al/sub 2/O/sub 3//ZnO films, with ultimate failure due to moisture-induced stiction and particulate contamination, not dielectric charging. The insertion loss and isolation for the switches was typically <0.35 dB and > 25 dBm, respectively, over a 10-25 GHz frequency range.

A frequency tunable half‐wave resonator using a MEMS variable capacitor

A frequency tunable half‐wave resonator at 3 GHz is presented with a microelectromechanical systems (MEMS) variable capacitor as the tuning element. The capacitor is fabricated using the multi‐user MEMS process (MUMPs) technology provided by JDS/Cronos, and transferred to an alumina substrate by an in‐house developed flip‐chip process. This capacitor is electrostatically actuated. The resulting C‐V response is linear with a slope of 0.05 pF/V for a wide range of actuation voltages. The MEMS device has a capacitance ratio of 3:1 for 0‐70 V bias, with a Q‐factor of 140 measured at 1 GHz. A half‐wave tunable microstrip resonator with bias lines is designed to include this MEMS device, which exhibits linear tuning over 180 MHz (6 percent) centered around 3 GHz with a constant 3 dB bandwidth of 160 MHz over the entire tuning range. The power consumption of the MEMS device was measured to be negligible.