Jeffrey F. Denatale

Low-loss 2- and 4-bit TTD MEMS phase shifters based on SP4T switches

2- and 4-bit microelectromechanical system (MEMS) X- to K/sub u/-band true-time-delay phase shifters with a very low insertion loss are described. The phase shifters are fabricated on 200-/spl mu/m GaAs substrates and the low loss is achieved using MEMS SP4T switches, which reduce the number of switches in the signal path by half when compared to conventional designs with SP2T switches. Measurements indicate an insertion loss of -0.6/spl plusmn/0.3 and -1.2/spl plusmn/0.5 dB at 10 GHz for the 2- and 4-bit designs, respectively. The measured losses agreed very well with Momentum simulations and are the lowest reported to date. The 2-bit phase shifter performed well from dc-18 GHz, with -0.8/spl plusmn/0.3-dB insertion loss at 18 GHz and a return loss of <-10.5 dB over dc-18 GHz.

Variable MEMS capacitors implemented into RF filter systems

A microelectromechanical systems analog tunable capacitor has been designed and fabricated for implementation into a two-pole UHF filter. Recent developments on the capacitor have improved the RF device performance significantly, and have resulted in improved UHF filter performance. In the 225-400-MHz range that this device is intended for, Q values are in excess of 100. In addition, an 8.4 : 1 tuning ratio has been achieved with continuous tuning over a 1.4 : 11.9-pF range. When implemented into a two-pole UHF filter, tuning over the entire 225-400-MHz range was achieved with a loss under 6.2 dB.

A Ka-band 3-bit RF MEMS true-time-delay network

A monolithic Ka-band true-time-delay (TTD) switched-line network containing 12 metal-to-metal contact RF microelectromechanical system switches has been successfully fabricated and characterized on a 75-/spl mu/m-thick GaAs substrate. The compact 9.1-mm/sup 2/ TTD network was designed to produce flat delay time over a dc-to-40-GHz bandwidth with full 360/spl deg/ phase control at 45/spl deg/ intervals at 35 GHz. Measurements show a match to within 2% to the designed delay times at 35 GHz for all eight switch states with 2.2-dB average insertion loss over all states. Peak rms phase error is 2.28/spl deg/ and peak rms amplitude error is 0.28 dB from dc to 40 GHz. Return loss better than 15 dB from dc to 40 GHz for all eight states confirms the circuits broad-band operation.

A novel MEMS LTCC switch matrix

A novel planar 4/spl times/4 switch matrix using microelectromechanical system (MEMS) switches and low temperature cofired ceramic (LTCC) substrate is presented for the first time. Together a 9-layer LTCC substrate and 32 MEMS switches are integrated to create a non-blocking 4/spl times/4 switch matrix functionality with excellent RF performance up to 7 GHz. An accurate model for predicting the interconnect circuit and switch matrix RF performance up to 20 GHz is also presented.

An isolated tunable capacitor with a linear capacitance-voltage behavior

A unique tunable capacitor has been designed that facilitates a completely isolated capacitance and a truly linear capacitance-voltage behavior. Using a low-temperature adhesive bonding process and device layer transfer techniques, a linear analog tunable capacitor has been fabricated and tested. The device shows a linear capacitance-voltage behavior using a +-10 V input voltage and tunes over a 1.78 to 3.88 pf range. The isolated design also allows greater flexibility in circuit design because the capacitor is not required to be a capacitor to ground.

A high Q, large tuning range, tunable capacitor for RF applications

Using a new, double-sided adhesive process, an analog tunable capacitor has been designed and fabricated with an extremely large tuning range and a high Q. New design components such as two-sided metal deposition, low resistivity silicon, thicker device layers, and double beam suspensions have improved RF performance drastically. In the 200-400 MHz range that this device is intended for, Q values are in excess of 100. In addition, an 8.4 to 1 tuning ratio has been achieved with continuous tuning over a 1.4 to 11.9 pF range. To further improve dynamic performance, devices were operated in a high viscosity gas environment and near critical damping was achieved.

A 2-bit miniature X-band MEMS phase shifter

The design and performance of a compact low-loss X-band true-time-delay (TTD) MEMS phase shifter fabricated on 8-mil GaAs substrate is described. A semi-lumped approach using microstrip transmission lines and metal-insulator-metal (MIM) capacitors is employed for the delay lines in order to both reduce circuit size as well as avoid the high insertion loss found in typical miniaturized designs. The 2-bit phase shifter achieved an average insertion loss of -0.70 dB at 9.45 GHz, and an associated phase accuracy of /spl plusmn/1.3/spl deg/. It occupies an area of only 5 mm/sup 2/, which is 44% the area of the smallest known X-band MEMS phase shifter . The phase shifter operates over 6-14 GHz with a return loss of better than -14 dB.

A very-low-loss 2-bit X-band RF MEMS phase shifter

A novel low-loss phase shifter, based on RF MEMS series switches and a single-pole four-throw (SP4T) switch design, is presented. The phase shifter is fabricated on a 200 /spl mu/m-thick GaAs substrate, and occupies less than 12 mm/sup 2/ of space. The measured average insertion loss is -0.55 dB, with a reflection loss of less than -17 dB over the 8-12 GHz frequency range. The 2-bit phase shifter performs well up to 18 GHz with an average loss of only -0.85 dB and a near-perfect linear phase shift from DC-18 GHz. This is the lowest loss MMIC-type phase shifter to-date at 8-18 GHz.

A hybrid approach to low-voltage MEMS switches

We have fabricated a hybrid MEMS switch that has improved mechanical performance over that of the traditional electrostatic switch. The hybrid switch uses the Lorentz force for actuation and electrostatics for the holding force. A short current pulse is passed along the suspension in the presence of a permanent magnetic field, thereby creating a lateral displacement. The displacement moves the micro-relay into contact and reduces the gap of the hold capacitors. Voltages as low as 1 V can be used to drive and hold the switch shut, without compromising contact force, hold force, restoring force, or response time. Additionally, the bi-directional nature of the Lorentz force allows for an active open of switches to counter contact adhesion. This approach offers additional design space for enhanced switch performance without compromising many of the desired qualities of a MEMS switch.

Microelectromechanical system radio frequency switches in a picosatellite mission

Rockwell Science Center (RSC) has designed and implemented a microelectromechanical-system- (MEMS-) based radio frequency switch experiment in a miniature satellite format (picosat) as an initial demonstration of MEMS for space applications. This effort is supported by DARPA-MTO, and the mission was conducted with Aerospace Corporation and Stanford University as partners. MEMS surface-micromachined metal contacting switches were manufactured and used in a simple, yet informative, experiment aboard the miniature satellites to study the device behavior in space, and its feasibility for space applications in general. Communication links between multiple miniature satellites, as well as between the satellites and ground, were also achieved using communications circuits constructed and provided by RSC. Details of both the MEMS and radio communications and networking efforts will be discussed in this paper.