Sebastian T. Bartsch

Ultra low power: Emerging devices and their benefits for integrated circuits

In this paper we analyze and discuss the characteristics and expected benefits of some emerging device categories for ultra low power integrated circuits. First, we focus on two categories of sub-thermal subthreshold swing switches Tunnel FETs and Negative Capacitance (NC) FETs and evaluate their potential advantages for digital and analog design, compared to CMOS. Second, we investigate the combined low power and novel integrated functionality in some hybrid Nano-Electro-Mechanical (NEM) devices: the Resonant Body (RB) Fin FET for nW time reference ICs and dense arrays of Suspended Body (SB) Double Gate (DG) Carbon Nanotube (CNT) FET for low power analog/RF and integrated sensor arrays.

Nanomechanical Silicon Resonators with Intrinsic Tunable Gain and Sub-nW Power Consumption

Nanoelectromechanical systems (NEMS) as integrated components for ultrasensitive sensing, time keeping, or radio frequency applications have driven the search for scalable nanomechanical transduction on-chip. Here, we present a hybrid silicon-on-insulator platform for building NEM oscillators in which fin field effect transistors (FinFETs) are integrated into nanomechanical silicon resonators. We demonstrate transistor amplification and signal mixing, coupled with mechanical motion at very high frequencies (25-80 MHz). By operating the transistor in the subthreshold region, the power consumption of resonators can be reduced to record-low nW levels, opening the way for the parallel operation of hundreds of thousands of NEM oscillators. The electromechanical charge modulation due to the field effect in a resonant transistor body constitutes a scalable nanomechanical motion detection all-on-chip and at room temperature. The new class of tunable NEMS represents a major step toward their integration in resonator arrays for applications in sensing and signal processing.

A single active nanoelectromechanical tuning fork front-end radio-frequency receiver

Nanoelectromechanical systems (NEMS) offer the potential to revolutionize fundamental methods employed for signal processing in todays telecommunication systems, owing to their spectral purity and the prospect of integration with existing technology. In this work we present a novel, front-end receiver topology based on a single device silicon nanoelectromechanical mixer-filter. The operation is demonstrated by using the signal amplification in a field effect transistor (FET) merged into a tuning fork resonator. The combination of both a transistor and a mechanical element into a hybrid unit enables on-chip functionality and performance previously unachievable in silicon. Signal mixing, filtering and demodulation are experimentally demonstrated at very high frequencies ( > 100 MHz), maintaining a high quality factor of Q = 800 and stable operation at near ambient pressure (0.1 atm) and room temperature (T = 300 K). The results show that, ultimately miniaturized, silicon NEMS can be utilized to realize multi-band, single-chip receiver systems based on NEMS mixer-filter arrays with reduced system complexity and power consumption.

Phase-locked loop based on nanoelectromechanical resonant-body field effect transistor

We demonstrate the room-temperature operation of a silicon nanoelectromechanical resonant-body field effect transistor (RB-FET) embedded into phase-locked loop (PLL). The very-high frequency resonator uses on-chip electrostatic actuation and transistor-based displacement detection. The heterodyne frequency down-conversion based on resistive FET mixing provides a loop feedback signal with high signal-to-noise ratio. We identify key parameters for PLL operation, and analyze the performance of the RB-FET at the system level. Used as resonant mass detector, the experimental frequency stability in the ppm-range translates into sub atto-gram (10(-18) g) sensitivity in high vacuum. The feedback and control system are generic and may be extended to other mechanical resonators with transistor properties, such as graphene membranes and carbon nanotubes

Wafer-Level Hysteresis-Free Resonant Carbon Nanotube Transistors

We report wafer-level fabrication of resonant-body carbon nanotube (CNT) field-effect transistors (FETs) in a dual-gate configuration. An integration density of >10(6) CNTFETs/cm(2), an assembly yield of >80%, and nanoprecision have been simultaneously obtained. Through combined chemical and thermal treatments, hysteresis-free (in vacuum) suspended-body CNTFETs have been demonstrated. Electrostatic actuation by lateral gate and FET-based readout of mechanical resonance have been achieved at room temperature. Both upward and downward in situ frequency tuning has been experimentally demonstrated in the dual-gate architecture. The minuscule mass, high resonance frequency, and in situ tunability of the resonant CNTFETs offer promising features for applications in radio frequency signal processing and ultrasensitive sensing.

Very high frequency double-ended tuning fork nano-mechanical Fin-FET resonator

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.

Junctionless Silicon Nanowire Resonator

The development of nanoelectromechanical systems (NEMS) is likely to open up a broad spectrum of applications in science and technology. In this paper, we demonstrate a novel double-transduction principle for silicon nanowire resonators, which exploits the depletion charge modulation in a junctionless field effect transistor body and the piezoresistive modulation. A mechanical resonance at the very high frequency of 100 MHz is detected in the drain current of the highly doped silicon wire with a cross-section down to ~ 30 nm. We show that the depletion charge modulation provides a ~ 35 dB increase in output signal-to-noise compared to the second-order piezoresistive detection, which can be separately investigated within the same device. The proposed junctionless resonator stands, therefore, as a unique and valuable tool for comparing the field effect and the piezoresistive modulation efficiency in the same structure, depending on size and doping. The experimental frequency stability of 10 ppm translates into an estimated mass detection noise floor of ~ 60 kDa at a few seconds integration time in high vacuum and at room temperature. Integrated with conventional semiconductor technology, this device offers new opportunities for NEMS-based sensor and signal processing systems hybridized with CMOS circuitry on a single chip.

Resonant-body Fin-FETs with sub-nW power consumption

This paper presents, for the first time, experimental evidence on resonant-body Fin-FETs (RB-FinFET) with two independent lateral gates, operated from weak to strong inversion, which enables unique trade-off between power consumption and gain. Resonance frequencies from 25 MHz to 80 MHz with quality factors of the order of 3000 and motional resistances of the order of tens of kOhm are demonstrated with a mixer mode measurement technique, dedicated to ultra-scaled resonators. The power consumption of the active resonators can be reduced in weak inversion of the RB-FinFET well below 1nW, which is a record value compared to any prior active NEM resonator.

Active NEM filters for communications applications based on vibrating body transistors

In this work we propose and demonstrate the first active Nano-Electro-Mechanical (NEM) filters based on scaled vibrating body field effect transistor (VB-FET) with mechanically coupled flexural-mode beam resonators working at a fundamental resonant frequency of 115MHz. The VB-FET filters are fabricated on a 200 nm thin SOI substrate using E-Beam lithography and sacrificial layer etching. Numerical simulations prove the validity of the design and allow a fine control of the center frequency and bandwidth via applied DC voltages. The measured DC characteristics show a working FET with threshold voltage at -3V and short channel effects. Despite the low signal-to-background ratio, direct S-parameter mesurements demonstrate the functionality and the tuneable gain of VB-FET based NEM-filters.

High performance 110 nm InGaAs/InP DHBTs in dry-etched in-situ refractory emitter contact technology

We report a 110 nm InP/In<inf>0.53</inf>Ga<inf>0.47</inf>As/InP double heterojunction bipolar transistor (DHBT) demonstrating a simultaneous f<inf>t</inf>/f<inf>max</inf> of 465/660 GHz and operating at power densities in excess of 50 mW/µm². To our knowledge this is the smallest junction width reported for a III–V DHBT. The narrow 110 nm emitter junction permits the devices to be biased simultaneously at high voltages and high current densities (J<inf>e</inf>) with peak RF performance at 41 mW/µm² (J<inf>e</inf> = 23.6 mA/µm², V<inf>ce</inf> = 1.75 V). Devices incorporate low contact resistance, refractory, in-situ Mo emitter contact to a highly doped, regrown InGaAs cap. A low stress, sputter deposited, refractory, dry-etched W/Ti<inf>0.1</inf>W<inf>0.9</inf> emitter metal process was developed demonstrating both high emitter yield and scalability to sub-100 nm junctions. Previously reported dry etch processes involving Ti/Ti<inf>0.1</inf>W<inf>0.9</inf> metals could not be scaled below 180 nm junction widths due to high metal stress resulting in very low emitter yield [1, 2]. The emitter metal contacts reported here are 100 nm wide and the emitter-base junction width is 110 nm. On-wafer Through-Reflect-Line (TRL) calibration structures were used to measure the RF performance of devices from 140 – 180 GHz.