J. De Coster

Dynamics and squeeze film gas damping of a capacitive RF MEMS switch

We report on measurements of the time-dependent capacitance of an RF MEMS shunt switch. A high time-resolution detection set-up is used to determine switching time and motion of the device. From the equation of motion the damping force is extracted. The measured damping force is found to be approximately proportional to the speed over the gap to the third power (FD v/z3), in good agreement with squeeze film damping theory. Significant influence of slip–flow effects on the motion is observed. Measurements at low pressure show underdamped harmonic oscillations in the opening motion and contact bounce effects in the closing motion. Effects of dielectric charging on the C–V curves are discussed. Experimental results are compared with electromechanical and damping simulations.

RF MEMS tunable capacitors with large tuning ratio

MEMS tunable capacitors have been fabricated in a thin-film technology for passive integration. Using a dual-gap relay-type design, continuous and reversible capacitance tuning with a tuning ratio up to 17 has been demonstrated, while requiring an actuation voltage of only 20 V. A quality factor of 150 to 500 has been measured in the frequency range of 1 to 6 GHz, making these devices very suitable as building blocks in many RF applications. These are the highest tuning ratio and quality factor reported to date for parallel-plate tunable capacitors.

Microelectromechanical tunable capacitors for reconfigurable RF architectures

This paper reports on metal-based MEMS tunable capacitors, fabricated in a thin-film process on high-ohmic silicon. Continuous and reversible tuning has been demonstrated with an average tuning ratio of 4.5. A quality factor between 100 and 300 has been obtained in a frequency range of 0.5 to 4 GHz. The combination of a high quality factor and large tuning range makes these tunable capacitors very suitable as building blocks in many radio-frequency (RF) applications. The tuning speed, temperature stability and RF power handling have been studied in terms of self-actuation. Finally, the need for a hermetic package as well as a packaging concept which can potentially provide this has been demonstrated. After packaging, the devices can be handled as standard silicon dies, making them fit very well with a system-in-package approach.

The influence of mechanical shock on the operation of electrostatically driven RF-MEMS switches

A closed-form relationship between the insertion loss, the externally applied mechanical shock and the RF signal voltage of a capacitive RF-MEMS shunt switch is derived. It is shown that, based on this relationship, the minimum required mechanical stiffness of the suspended structure can be calculated. This allows determination of the minimum electrostatic switching voltage in a given process flow. The results are illustrated for specifications regarding shock resistance of electronic equipment as set out in MIL-STD-883. Even under the least severe test conditions, the shocks can affect the insertion loss of RF-MEMS switches, and can provoke self-biasing. This paper gives guidelines to avoid such false operation modes. The method can also be extended to yield the sensitivity of RF-MEMS devices to harmonic vibrations.

Variable RF MEMS capacitors with extended tuning range

Three distinct designs of variable RF MEMS capacitors are presented and a comparison is made in terms of their continuous tuning range. Among these designs are the classical parallel-plate capacitor, as well as the so-called two-gap structure and a novel device with torsion-beam suspensions and double actuation. This allows the capacitance to be tuned over a larger range compared to a single-driven device. As a result of this, the tuning range of the device exceeds the theoretical 50%-limit for parallel-plate capacitors. The tuning ranges of all three devices have been determined experimentally and were found to be 39% for the parallel-plate capacitor, 310% for the two-gap structure and 61% for the torsion-suspension device. The measured tuning voltages are 17 V, 22 V and 11 V respectively.

-1 V bias 67GHz bandwidth Si-contacted germanium waveguide p-i-n photodetector for optical links at 56 Gbps and beyond

We demonstrate a 67 GHz bandwidth silicon-contacted germanium waveguide p-i-n photodetector operating at -1 V with 6.8 fF capacitance. The dark current is below 4 nA. The responsivity is 0.74 A/W at 1550 nm and 0.93 A/W at 1310 nm wavelength. 56 Gbps on-off-keying data reception is demonstrated with clear open eye diagrams in both the C-band and O-band.

Highly reliable CMOS-integrated 11MPixel SiGe-based micro-mirror arrays for high-end industrial applications

In this paper we report for the first time on the fabrication of very reliable CMOS-integrated 10 cm2 11 MPixel SiGe-based micro-mirror arrays on top of 6 level metal CMOS wafers. The array, which is to be used as Spatial Light Modulator (SLM) for optical maskless lithography [1,2,3] consists of 8 mum x 8 mum pixels which can be individually addressed by an analog voltage to enable accurate tilt angle modulation. The pixel density is almost double compared to the state-of-the-art [4]. A stable average cupping below 7 nm, an RMS roughness below 1 nm and long lifetime (>1012 cycles, no creep [5]) are demonstrated.

11-Megapixel CMOS-Integrated SiGe Micromirror Arrays for High-End Applications

In this paper, we report on the design, fabrication, packaging, and testing of very reliable CMOS-integrated 10-cm2 11-megapixel SiGe-based micromirror arrays on top of planarized six-level metal 0.18-¿m CMOS wafers. The array, which is to be used as a spatial light modulator (SLM) for optical maskless lithography, consists of 8 ¿m × 8 ¿m pixels, which can be individually addressed by an analog voltage to enable accurate tilt angle modulation. Due to very stringent requirements on mounted-die flatness (< 0.01 mrad), the first level packaging of SLM die is done using specially designed SiC holders. To avoid trapped particles between the die and holder, which would jeopardize the flatness spec, special backside cleaning of the dies (less than or equal to one 0.8-¿m particle/cm2) is needed before mounting the SLM die on the holder. To enable this backside cleaning and to avoid front-side particles during dicing, handling, and wire bonding, a temporary waferor zero-level packaging cap, which can be placed and removed at room temperature, was developed. The dynamic white light interferometer measurements of packaged dies showed that 99.5% of the 123 648 mirrors tested are within the spec. In addition, a stable average cupping of below 7 nm, an rms roughness of below 1 nm, and a stable actuation of over 2.5 teracycles are demonstrated.

High-Q torsional mode Si triangular beam resonators encapsulated using SiGe thin film

This paper reports on an SOI-based 20 MHz MEMS torsional resonator, wafer-level packaged using SiGe thin film and hermetically sealed using Al sputtering at 1Pa. The packaged resonators display a high quality factor (220,000) and a low motional resistance (12 k Ω) for low DC bias (1 V). The quality factor remains above 100,000 and the temperature coefficient of frequency (TCf) was measured to be −25ppm/°C and linear over the temperature range of −40 to +140 °C. Successful operation of a CMOS-based oscillator using the MEMS torsional resonator as the frequency determining element was demonstrated.

Above-IC generic poly-SiGe thin film wafer level packaging and MEM device technology: Application to accelerometers

We present an attractive poly-SiGe thin film packaging and MEM (Micro Electro-Mechanical) platform technology for integrating various packaged MEM devices above standard CMOS. The packages, having cavities as large as 1mm2, make use of pillars designed to withstand subsequent molding during 1st level packaging. Covers on top of the release holes avoid deposition inside the cavity during sealing. Hermeticity is proven in vacuum, air and N2 atmosphere and at different temperatures. Packaged functional accelerometers sealed at a pressure around 1bar, have an equivalent performance in measuring accelerations of about 1g compared to a piezoelectric commercial reference device.