P. Dainesi

Reliability of RF MEMS Capacitive Switches and Distributed MEMS Phase Shifters using AlN Dielectric

The reliability and charging/discharging dynamics of wideband (1.5-14GHz) phase shifters made of MEMS capacitive switches using Aluminum Nitride (AlN) as dielectric are originally reported. Phase shifter lifetimes exceeding 109 cycles are achieved in hot-cycling (+5dBm RF power). Dynamic tests were done for the first time under ambient conditions (50% humidity) over 2×109 cycles with no major degradation of individual switches performances. It is demonstrated that the phase shifter is very robust (no permanent failure or stiction) and can withstand environmental effects as well as high temperature variations, without the need of expensive hermetical packaging. The excellent reliability is attributed to the slow dielectric charging (a square-root time law) and fast discharging mechanism of AlN (an exponential time law proposed and validated in our work). We extend the validity of charging and discharging models from single device to arrays of parallel MEMS capacitors.

Local volume inversion and corner effects in triangular gate-all-around MOSFETs

We report on the fabrication and measurement of triangular gate-all-around (GAA) and tri-gate devices. On the small triangular cross-section devices we observe a significant enhancement of the extracted carrier mobility (up to ~1000cm2/Vs). We assign this effect to enhanced conduction in the sharp corners of our device, and local volume inversion. The new concept of local volume inversion is supported by a boosting of experimental gm in the subthreshold region. Furthermore, we have carried out 3D numerical simulations, which support these findings

Experimental study of the process dependence of Mo, Cr, Ti, and W silicon Schottky diodes and contact resistance

This paper reports on the process dependence and electrical characterization of Schottky diodes and ohmic contacts fabricated on p- and n-type silicon wafers. Four metals are systematically studied using identical test structures and characterization methods: Mo, Ti, W, and Cr. The choice of these metals is motivated by their midgap barriers and compatibility with an integrated circuit technology. For these, a thorough investigation of the variation in Schottky-barrier height and contact resistance is carried out for the following process parameters: 1) predeposition wafer preparation, 2) deposition method (sputtering and e-beam evaporation), 3) deposition temperature for the sputtered samples, and 4) annealing. It is found that RF etching previous to metal deposition increases the contact resistance and the barrier height for diodes on p-type silicon. This is of great importance, since RF etching is a very common in situ cleaning process in microelectronic and microelectromechanical systems technologies. Annealing can be used to restore the values of barrier height and contact resistance on wafers exposed to the RF etching.

Fast and efficient light intensity modulation in SOI with gate-all-around transistor phase modulator

We report fast modulation (>30 GHz) in a SOI resonant cavity using integrated Bragg mirrors and a gate-all-around transistor as active element. Modulation depth >90% can be obtained in 12.5 /spl mu/m long devices.

3-D integrable optoelectronic devices for telecommunications ICs

3-D integrable SOI optoelectronic devices include telecommunication optical switches with 5 MHz bandwidth and unbalanced Mach Zehnder interferometers for filtering. Thermal compensation provides efficient modulation over 100 kHz -1 MHz and addresses 3-D IC thermal issues.

Scaling SOI photonics to micron and sub-micron devices

Scaling photonics devices in silicon on insulator (SOI) substrates has the potential to address important issues in the fields of optical telecommunications and optical interconnects. Silicon, is highly transparent in the infra-red spectral region and etching ribs or rectangular channels can create the condition for single-mode low-loss waveguiding. The high index difference between silicon and the surrounding media, typically SiO2 or air, is extremely favorable for the development of ultra-compact photonic devices. Active functionality can be performed by free charge injection in the waveguide resulting in a phase shift of the propagating fundamental mode. Moreover this technology is fully CMOS compatible allowing a low-cost monolithic integration of control electronics. Limitations deriving from an aggressive scaling of SOI waveguides are a lowered efficiency in the in-out coupling of light and higher propagation losses due to increased roughness scattering. We report on the perspectives and issues of scaling SOI photonics devices for both passive and active functionality. Results show that scaled waveguides can have very low bending radii down to the micrometer range. We also propose a new method and architecture for light phase modulation based on a Schottky barrier diode; a process flow will be analyzed and validated experimentally.

A novel CMOS SOI unbalanced Mach-Zehnder interferometer: from design and simulations to fabrication and characterization

This paper reports on a novel, simple yet reliable, unbalanced SOI Mach-Zehnder (M-Z) interferometer architecture based on 1.2 /spl mu/m CMOS process and adapted post-processing for the waveguide sidewalls. The fabricated electro-optical device is based on multiple PIN diode bars integrated on top of a SOI silicon waveguide and can be operated either at: (I) high-frequency (few MHz) based on the plasma dispersion effect and (II) low frequency (<1 MHz) based on the thermo-optic effect. The device main characteristics and figures of merit are presented and discussed.

Compact gate-all-around silicon light modulator for ultra high speed operation

We propose a novel, compact and ultra-high speed optical modulator, the performance of which is validated by 2D and 3D simulations. The light phase modulation is achieved by a gate-all-around (GAA) capacitive structure. The good overlap between the optical mode and the modulated region provides an efficient and fast modulation. A compact and fully integrated intensity modulator can be obtained by placing the GAA modulator in a resonant structure. We analyze the effects of sub-micron scaling on both optical and electrical performance. Maximum frequencies of operation beyond 10 GHz are predicted for a cross section 340/spl times/340 nm/sup 2/ and /spl mu/m modulator lengths.