Dimitrios Tsamados

Analytical Modeling of the Suspended-Gate FET and Design Insights for Low-Power Logic

An analytical model for the suspended-gate field-effect transistor (SGFET), dedicated to the dc analysis of SGFET logic circuits, is developed. The model is based on the depletion approximation and expresses the pull-in voltage, the pull-out voltage, and the stable travel range as a function of the structural parameters. Gate position is explicitly expressed as a function of the gate voltage, thus enabling the convenient integration of the analytical SGFET relationships into the standard MOSFET models. Starting from the new SGFET model, the influence of the mechanical hysteresis on the circuit steady-state behavior is discussed, the potential of using the SGFET as an ultra-low power switch is demonstrated, and the operation of the complementary SGFET inverter is analyzed.

Bended Gate-All-Around Nanowire MOSFET: a device with enhanced carrier mobility due to oxidation-induced tensile stress

In this paper we investigate the mobility enhancement due to strain in bended NW MOSFETs. Stress of 200 MPa to 2 GPa, induced by thermal oxidation, is measured in suspended NW FETs by Raman spectroscopy. Mobility enhancement of more than 100% is observed. Performance gain of bended compared to non-bended structures is most pronounced in low field conditions and at low temperatures.

Multi-gate vibrating-body field effect transistor (VB-FETs)

This paper reports on the design, fabrication and detailed characteristics of multi-gate vibrating-body field effect transistors (VB-FETs). Double-gate and four-gate VB-FETs with resonance frequencies of 2 MHz and 71 MHz, respectively, are successfully demonstrated. The VB-FETs exhibit built-in amplification (more than +30 dB improvement of signal detection compared with capacitive detection), low motional resistances (in the orders kOhms down to tens of Ohms) and frequency tuning by applied voltages. For the first time, we experimentally demonstrate an active MEM resonator concept, with built-in amplification, which has a negative resistance of -30 Ohms, enabling the possibility to build an oscillator without any sustaining amplifier, thus reducing the power consumption and oscillator size. Also for the first time, we demonstrate a VB-FET mixer-filter based on a single-device operating at 9.84 MHz and a VB-FET oscillator at 2.6 MHz.

Bulk Lateral MEM Resonator on Thin SOI With High

The fabrication, design, and characterization of high-quality factor microelectromechanical (MEM) resonators fabricated on thin-film silicon-on-insulators (SOIs) are addressed in this paper. In particular, we investigate laterally vibrating bulk-mode resonators based on connected parallel beams [parallel beam resonators (PBRs)]. The experimental characteristics of PBRs are compared to disk resonators and rectangular plate resonators. All the reported MEM resonators are fabricated on 1.25-mum SOI substrates by a hard mask and deep reactive-ion etching process, resulting in transduction gaps smaller than 200 nm. Additionally, this fabrication process allows the growth of a thermal silicon dioxide layer on the resonators, which is used to compensate the resonance-frequency dependence on temperature. Quality factors Q, ranging from 20 000 at 32 MHz up to 100 000 at 24.6 MHz, are experimentally demonstrated. The motional resistances R m are compared for different designs, and values as low as 55 kOmega at 18 V of bias voltage are obtained with the thin SOI substrate. The thermal sensitivity of the resonance frequency is investigated from 200 K to 360 K, showing values of -15 ppm/K for the PBRs, with a possible compensation of 2 ppm/K when using 20 nm of SiO2.

Q

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.

-Factor

Micro-electromechanical (MEM) laterally vibrating square resonators and beams, fabricated via a prototyping technology combining FIB-micromachined gaps with conventional UV lithography in 1.35 mum thick SOI are presented. Resonators with both capacitive and MOSFET detection and gaps of ~100 nm are demonstrated. Resonance frequencies of 32 MHz and 13 MHz were measured for squares and beams, respectively. The square shaped resonators have Q-factors in the order of 4000. This paper reports on a vibrating body MOS transistor active detection scheme integrated in a MEMS fabrication process to improve the signal read out.

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

For the first time, a compact model for suspended gate (SG) FET valid for entire bias range is proposed. The model is capable of simulating both pull-in and pull-out effects, which are the two important phenomena of this device. A novel hybrid numerical simulation approach combining ANSYS Multiphysics and ISE-DESSIS in a self-consistent system is developed. The model is then validated on this numerical device simulation of SGFET. The model shows excellent performance over the entire drain and gate voltage range. The model has been implemented in Verilog-A code and tested on ELDO and Spectre simulators, which makes it useful for circuit simulations using SGFET devices.

Integration of MOSFET Transistors in MEMS Resonators for Improved Output Detection

This paper discusses three categories of small slope electronic switches: the tunnel FET, the IMOS and the NEM-FET, which are expected to bring added value compared to CMOS by presenting an abrupt subthreshold slope, smaller than the physical limit, 60mV/decade, of the solid-state MOS transistor at room temperature. Recent results and future promises are reported.

Compact Modeling of Suspended Gate FET

This paper reports on the fabrication, experimental characterization and data transmission application of a double-gate movable body FET. As its name suggests, the proposed movable-body Micro-Electro-Mechanical FET (MB-MEMFET) is a hybrid MEMS-semiconductor device that, in contrast with previously reported Suspended-Gate MOSFET, has a movable body separated by nano-size air gaps from two lateral fixed gates. We report here on the unique abrupt hysteretic characteristic of MB-MEMFET, which for our design offer reproducibility after intense cycling and, due to double gate architecture, a multi-level tunable hysteresis. Based on the ID-VG hysteretic behavior of the new hybrid device we report for the first time a FSK circuit exploiting oscillation at two selectable frequencies (26 kHz and 14 kHz) used to transmit numerical data, which demonstrates the potential of the MB-MEMFET for applications in data transmission systems.

Small Slope Micro/Nano-Electronic Switches

We present the very high frequency (VHF) operation of a nano-mechanical double-ended tuning fork resonator (DETF), in which two fin field effect transistors (FinFET) are co-integrated. We benefit from the excellent mixing properties of the FinFET to characterize accurately its fundamental resonance (f0=113 MHz) and quality factor (Q=1300) and compare these results with clamped-clamped (cc-) beam FinFET resonators of similar dimensions. We find the tuning fork design to be superior in terms of Q-factors, transconductance and available on-current.