Yu-Shiang Lin

A sub-pW timer using gate leakage for ultra low-power sub-Hz monitoring systems

In this work, we present a novel ultra-low power timer designed using the gate leakage of MOS capacitors. The test chip was fabricated in a 0.13 mum CMOS technology and the total circuit area is 480 mum2. Measurement results show that the circuit functions correctly at a wide range of supply voltages from 300 mV to 1.2 V, making it particularly suitable for subthreshold systems. The temperature sensitivity is 0.16%/degC at 600 mV and 0.6%/degC at 300 mV. The power dissipation is less than 1pW running at 20degC and 300 mV.

An ultra low power 1V, 220nW temperature sensor for passive wireless applications

This work presents a low power temperature sensor that is suitable for passive wireless systems. The test chip is fabricated with a 0.18 mum CMOS technology and the total area is 0.05 mm2. With temperature inaccuracy of -1.6degC/+3degC from 0degC to 100degC, the temperature sensor consumes only 220 nW at 1V under room temperature. The data conversion rate is 100 sample/s with an output resolution of 0.3degC, which is sufficient for most sensor applications.

A Millimeter-Scale Energy-Autonomous Sensor System With Stacked Battery and Solar Cells

An 8.75 mm3 microsystem targeting temperature sensing achieves zero-net-energy operation using energy harvesting and ultra-low-power circuit techniques. A 200 nW sensor measures temperature with -1.6 °C/+3 °C accuracy at a rate of 10 samples/sec. A 28 pJ/cycle, 0.4 V, 72 kHz ARM Cortex-M3 microcontroller processes temperature data using a 3.3 fW leakage per bit SRAM. Two 1 mm2 solar cells and a thin-film Li battery power the microsystem through an integrated power management unit. The complete microsystem consumes 7.7 μ W when active and enters a 550 pW data-retentive standby mode between temperature measurements. The microsystem can process temperature data hourly for 5 years using only the initial energy stored in the battery. This lifetime is extended indefinitely using energy harvesting to recharge the battery, enabling energy-autonomous operation.

Record high RF performance for epitaxial graphene transistors

By optimizing of the gate dielectrics and device dimensions, we achieve a record high output current and transconductance of 5 mA/µm and 2 mS/µm in epitaxial graphene FETs. A cut-off frequency of 280 GHz is achieved for a 40-nm graphene FET, the highest so far on any synthesized graphene. Also, highest voltage gain of 10 dB has been achieved, with an f<inf>max</inf>/f<inf>T</inf> ratio larger than 1 demonstrated consistently on different devices. For the first time, forward power gain |S<inf>21</inf>|>1 delivered into a 50-Ω load is demonstrated.

RF performance of short channel graphene field-effect transistor

We have experimentally demonstrated the high performance short channel RF graphene device with cut-off frequency of 170 GHz on epitaxial graphene on SiC. We have also studied performance improvement by reducing contact resistance at lower measurement temperature for short channel device. The study shows continuous performance improvement can be achieved by proper channel length scaling and structure optimization such as self-aligned gate and technological solutions for contact resistance reduction.

Novel structures enabling bulk switching in carbon nanotube FETs

In order to alleviate the disadvantages associated with Schottky barriers in CNFETs, it is necessary to design CNFETs with bulk switching properties meaning that the bulk portion of the nanotube rather than the interface controls the CNFET characteristics. Here we present the first self-aligned bulk-switched CNFET that operates in the enhancement mode with a p-i-p (or n-i-n) doping profile along the tube. With our novel approach, we successfully fabricated CNFETs with excellent switching (S/spl sim/63 mV/dec), the smallest value reported for CNFETs so far, and very good performance in terms of their drain-induced-barrier-lowering (DIBL)-like behavior.

Graphene-based fast electronics and optoelectronics

We present experimental results on high frequency field-effect transistors and fast photodetectors utilizing wafer-scale graphene grown epitaxially from silicon carbide.

Low-voltage circuit design for widespread sensing applications

Ubiquitous computing has a number of compelling applications ranging from biomedical sensing to environmental monitoring. These computing systems require low cost sensor nodes with volumes <1mm3 and lifetimes on the order of months or years. We advocate the use of aggressively scaled supply voltages in such applications to maximize energy efficiency. This paper reviews our recent progress in mapping out the low energy design space. We explore the design and test of three low voltage systems targeting ubiquitous computing. We conclude with a survey of open research directions in the ultra-low energy design space.

An extended model for carbon nanotube field-effect transistors

In this paper, we present an extended Schottky barrier model that includes two new crucial aspects: i) current injection from the metal contacts into the channel does not occur directly but is mediated by the segment of the nanotube underneath the metal contacts whose density of states (DOS) is altered through the proximity of the metal (referred to in the following as metal-modified nanotube segment); and ii) the energy gap of carbon nanotubes with an average diameter of /spl sim/1.4 nm seems to be rather /spl sim/1.2 eV than /spl sim/0.7 eV as typically assumed for these type of tubes. Our simulation allows us for the first time to quantitatively describe subthreshold characteristics of CNFETs over the entire gate voltage range.

Near-field communication using phase-locking and pulse signaling for millimeter-scale systems

An inductive coupling based proximity communication system is proposed for data readout of remote powered sensor systems with ultra small form factor in ñmm3 range for implantable applications. The passive transponder is powered with a 1×1mm on-chip inductor, which also enables readout signaling using pulse signaling. The required resonance frequency for pulse signaling is obtained using a transponder PLL that locks to the incoming frequency transmitted by the reader system. Communication with a passive 1mm2 sensor node implemented in 0.13µm technology is demonstrated.