Quentin Diduck

A ROOM TEMPERATURE BALLISTIC DEFLECTION TRANSISTOR FOR HIGH PERFORMANCE APPLICATIONS

The Ballistic Deflection Transistor (BDT) is a novel device that is based upon an electron steering and a ballistic deflection effect. Composed of an InGaAs-InAlAs heterostructure on an InP substrate, this material system provides a large mean free path and high mobility to support ballistic transport at room temperature. The planar nature of the device enables a two step lithography process, as well, implies a very low capacitance design. This transistor is unique in that no doping junction or barrier structure is employed. Rather, the transistor utilizes a two-dimensional electron gas (2DEG) to achieve ballistic electron transport in a gated microstructure, combined with asymmetric geometrical deflection. Motivated by reduced transit times, the structure can be operated such that current never stops flowing, but rather is only directed toward one of two output drain terminals. The BDT is unique in that it possesses both a positive and negative transconductance region. Experimental measurements have indicated that the transconductance of the device increases with applied drain-source voltage. DC measurements of prototype devices have verified small signal voltage gains of over 150, with transconductance values from 45 to 130 mS/mm depending upon geometry and bias. Gate-channel separation is currently 80nm, and allows for higher transconductance through scaling. The six terminal device enables a normally differential mode of operation, and provides two drain outputs. These outputs, depending on gate bias, are either complementary or non-complementary. This facilitates a wide variety of circuit design techniques. Given the ultralow capacitive design, initial estimates of ft, for the device fabricated with a 430nm gate width, are over a THz.

3,000+ Hours continuous operation of GaN-on-Diamond HEMTs at 350°c channel temperature

The authors report for the first time the observation of GaN-on-Diamond HEMTs each operating continuously at channel temperatures of 290°C and 350°C for 9,000+ hrs and 3,000+ hrs respectively per HEMT. No catastrophic failures were observed whereas all the control GaN-on-Si HEMTs exhibited catastrophic failures.

SIMULATION AND EXPERIMENTAL RESULTS ON GaN BASED ULTRA-SHORT PLANAR NEGATIVE DIFFERENTIAL CONDUCTIVITY DIODES FOR THz POWER GENERATION

A GaN based negative differential conductivity diode utilizing transient ballistic transport effects is proposed and large-signal circuit simulations along with preliminary experimental results are presented. The diode is an n+-n-n+ structure and transport is described by an empirical velocity-field relation which is derived directly from femtosecond pulse-probe measurements available in literature and incorporated into the simulations through curve fitting. Efficient THz generation is predicted as a result of ~2.8 peak-to-valley ratio. Pulsed current-voltage characteristics were measured and N-type dependence was observed.

6-bit low power low area frequency modulation based flash ADC

This paper presents a 6-bit frequency modulation based ADC design. The demonstrated design yields a device that uses less than 10% of the power of comparable designs. In addition, this architecture provides a simple and logical way to trade sampling rate for accuracy. The presented device has a power consumption of 30mW while operating at approximately 1.05 GSample/sec with an INL and DNL values of 0.23 and 0.4/-0.3 LSB respectively. The design has been implemented in a 1.8 volt 0.18/spl mu/m CMOS process.

Importance and measurement of phase-stiffness in RF switching amplifiers

Phase-stiffness is a measure of the ability of an RF power amplifier to tolerate disturbance injected into its output. Phase-stiffness of conventional (linear) RF power amplifiers used in phased-array radar results from inserting circulators and isolators on their output as they can not tolerate typical disturbances arising from antenna mismatch and signals arriving from mutual coupling of array elements. We show that the output stage of a RF switching amplifier employing a single AlGaN/GaN HEMT loaded with an inductor exhibits high tolerance to external signal disturbance at the carrier frequency. This RF amplifier architecture shows promise for use in phase-array radar and active antenna array transmit/receive modules as this may operate without isolators.

Process tolerant calibration circuit for PLL applications with BIST

A process-invariant calibration circuit, capable of correcting performance errors in charge-pump based PLLs is described. Process variations detrimentally affect all building blocks of standard PLL architectures. Utilizing a novel ADC, these variations are sensed and corrected. The self-calibration circuitry is non-intrusive and requires minimal area and power overhead. A case study of a 2.4GHz ring VCO-based PLL designed in a TSMCs 0.18mum CMOS mixed-signal technology is given. The calibration circuitry is able to sense and calibrate under all four process corners as well as detect under high temperature conditions

Class-D GaN 15MHz-bandwidth amplitude modulator with a direct CMOS interface

Switching supply modulators are key in achieving reasonable energy efficiency in a polar amplitude modulating RF power amplifier. However, achieving good conversion efficiency, high tracking bandwidth and low switching harmonic feedthrough at high power are challenging to meet at the same time. GaN technology is a viable candidate for this task, but signal interfacing and level shifting at high switching rates can be difficult and power hungry. Here we present a 100MHz GaN switching, multi-stage, highly integrated class-D amplifier that can be driven with a single ended CMOS level PWM signal. It provides up to 3.5W of power with 83% efficiency and 15MHz Fourier-flat bandwidth with less than 20mVpp ripple.

A fully polar transmitter for efficient software-defined radios

While polar modulation is a transmitter technique that is known to maximize energy efficiency, it also has no circuit linearity and traditionally is unable to produce signals that contain envelope zeros such as QAM and LTE. This polar transmitter solves this weakness and is modulation agnostic across the decade-wide tuning bandwidth of 200–2500 MHz. In particular, a conventional Nyquist filtered 256QAM signal is generated with error vector magnitude (EVM) less than 1.5% across the frequency range, and is below 1% across the bottom decade of frequency — without use of digital predistortion (DPD) linearization. Peak output power is 2.5 watts.

Minimization of maximum electric field in high-voltage parallel-plate capacitor

Minimization of maximum electric field of a parallel-plate capacitor for high-voltage and temperature stable applications is presented. Cubic zirconia is used as a dielectric material because of its high relative permittivity, high dielectric strength and high temperature stability. The maximum electric field present in the structure limits the maximum achievable capacitance of the capacitor structure. Reducing the maximum electric field of the capacitor allows to reduce the thickness of the dielectric material, which increases its capacitance. The impact of geometrical and electrical parameters of the parallel-plate capacitor on the maximum electric field is analyzed by a 2D multiphysics solver. The guidelines for the minimization of the maximum electric field are given.

NOVEL HIGH TEMPERATURE ANNEALED SCHOTTKY METAL FOR GaN DEVICES

We have found that Scandium metal is near ohmic as deposited on GaN, but when it is annealed at high temperatures a large barrier height Schottky forms. In this study we used Sc-Au contacts to form Schottky barrier diodes on AlGaN/GaN HEMT material. We have found that the morphology remains unchanged even after an 800 degrees centigrade anneal. This investigation has revealed that the reverse leakage current of this metal system is an order of magnitude lower than a conventional Ni-Au contact and supports a reverse breakdown that is 1/3rd larger. The similarity of the anneal temperatures to ohmic contacts enable gates and contacts to be annealed at the same time thus simplifying processing. The lack of morphology change supports the use of Sc-Au for E-beam alignment marks as well. Diode contacts on AlGaN/GaN with Schottky-ohmic separation of 10 microns demonstrated reverse breakdown in excess of 100V when the contacts were annealed at 800C. These results suggest this metallization may have applications as a new HEMT gate metal, and Schottky diodes.