I. Milosavljevic

GaN HFET for W-band Power Applications

In this paper we report high frequency GaN power device and measured power performance of the first W-band (75 GHz-110 GHz) MMIC fabricated in GaN material system. The first W-band GaN MMIC with 150 mum of output gate periphery produces 316 mW of continuous wave output power (power density =2.1 W/m) at a frequency of 80.5 GHz and has associated power gain of 17.5 dB. By comparison the reported state of the art for other solid state technologies in W-band is 427 mW measured in a pulsed mode on an InP HEMT MMIC with 1600 mum of output periphery (power density = 0.26 W/mm). The reported result demonstrates tremendous superiority of GaN device technology for power applications at frequencies greater than 75 GHz

GaN double heterojunction field effect transistor for microwave and millimeterwave power applications

We report development of a novel AlGaN/GaN/AlGaN double heterojunction field effect tansistor (DHFET) with improved device performance over the conventional single heterojunction GaN FET (SHFET). The GaN DHFETs with low Al content Al/sub 0.04/Ga/sub 0.96/N buffer layer exhibit three orders of magnitude lower subthreshold drain leakage current and almost three orders of magnitude higher buffer isolation than corresponding SHFET devices (600 M/spl Omega//sq. vs. 1 M/spl Omega//sq.). In GaN DHFETs with 0.15 /spl mu/m conventional T-gates we observed 30% improvement in saturated power density and 10% improvement in PAE at 10 GHz over a corresponding SHFET device.

Isotopically enhanced triple-quantum-dot qubit

Three coupled quantum dots in isotopically purified silicon enable all-electrical qubit control with long coherence time. Like modern microprocessors today, future processors of quantum information may be implemented using all-electrical control of silicon-based devices. A semiconductor spin qubit may be controlled without the use of magnetic fields by using three electrons in three tunnel-coupled quantum dots. Triple dots have previously been implemented in GaAs, but this material suffers from intrinsic nuclear magnetic noise. Reduction of this noise is possible by fabricating devices using isotopically purified silicon. We demonstrate universal coherent control of a triple-quantum-dot qubit implemented in an isotopically enhanced Si/SiGe heterostructure. Composite pulses are used to implement spin-echo type sequences, and differential charge sensing enables single-shot state readout. These experiments demonstrate sufficient control with sufficiently low noise to enable the long pulse sequences required for exchange-only two-qubit logic and randomized benchmarking.

92–96 GHz GaN power amplifiers

We report the test results of a family of 92-96 GHz GaN power amplifiers (PA) with increasing gate peripheries (150 µm to 1200 µm). The 1200 µm, 3-stage PA produces 2.138 W output power (Pout) with an associated PAE of 19% at 93.5 GHz (VD=14V). The amplifier offers Pout over 1.5W with associated PAE over 17.8% in the 92–96 GHz bandwidth. The measured data show that the maximum Pout scales linearly with increasing gate periphery at an almost constant PAE around 20%. This demonstrates the high efficiency of on-chip power combining and enables W-band high power single chip solid state power amplifiers.

W-Band GaN MMIC with 842 mW output power at 88 GHz

We report W-band GaN MMICs that produce 96% more power at a frequency of 88 GHz in continuous wave (CW) operation than the highest power reported in this frequency band for the best competing solid state technology[1], the InP HEMT. W-band power module containing a single three stage GaN MMIC chip with 600 µm wide output stage produced over 842 mW of output power in CW-mode, with associated PAE of 14.7% and associated power gain of 9.3 dB. This performance was measured at MMIC drain bias of 14 V.

Electron Velocity Enhancement in Laterally Scaled GaN DH-HEMTs With

In this letter, we report the first experimental observation of electron velocity enhancement by aggressive lateral scaling of GaN HEMTs. Through reduction of the source-drain distance down to 170 nm using <i>n</i>⁺-GaN ohmic regrowth, 45-nm gate AlN/GaN/Al_0.08Ga_0.92N HEMTs exhibited an extremely small on resistance of 0.44 Ω·mm , a high maximum drain current density of 2.3 A/mm, a high peak extrinsic transconductance of 905 mS/mm, and a record <i>fT</i>/<i>f</i>_max of 260/394 GHz. Delay time analysis showed that the outstanding <i>fT</i> was mainly due to significantly reduced electron transit time at higher drain-source voltages resulting from suppressed drain delay and enhanced electron velocity in the laterally scaled GaN HEMTs.

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In this paper we demonstrate the merits of GaN MMIC technology for high bandwidth millimeter-wave power applications and for microwave robust LNA receiver applications. We report the development of a broadband two-stage microstrip Ka-band GaN MMIC power amplifier, with 15dB of flat small signal gain over the 27.5GHz to 34.5GHz frequency range and 4W of saturated output power at 28GHz, with a power added efficiency of 23.8%. This is to the best of our knowledge the best combination of output power, bandwidth and efficiency reported for a GaN MMIC in Ka-band frequency range. We also report a robust two-stage wideband (0.5GHz-12GHz) GaN LNA MMIC, which can survive 4W of incident input RF power in CW mode without input power protective circuitry. The presented LNA MMIC has, to the best of our knowledge, the best combination of NF, bandwidth, survivability and low power consumption reported to date in GaN technology.

of 260 GHz

We demonstrate improved operation of exchange-coupled semiconductor quantum dots by substantially reducing the sensitivity of exchange operations to charge noise. The method involves biasing a double dot symmetrically between the charge-state anticrossings, where the derivative of the exchange energy with respect to gate voltages is minimized. Exchange remains highly tunable by adjusting the tunnel coupling. We find that this method reduces the dephasing effect of charge noise by more than a factor of 5 in comparison to operation near a charge-state anticrossing, increasing the number of observable exchange oscillations in our qubit by a similar factor. Performance also improves with exchange rate, favoring fast quantum operations.

GaN MMIC technology for microwave and millimeter-wave applications

An enhancement-mode (E-mode) AlN/GaN/AlGaN double-heterojunction field-effect transistor (DHFET) with record high-frequency performance is reported. E-mode operation was achieved through vertical scaling of the AlN barrier layer. Parasitic resistances were reduced through ohmic contact recess etching followed by regrowth of n+ GaN by molecular-beam epitaxy and SiN deposition to increase the sheet charge density in the access regions of the device, resulting in an extremely low on-resistance of 1.06 Ω · mm. A DHFET with an 80-nm gate length had a threshold voltage of 0.21 V, an extrinsic transconductance (gm) of 0.70 S/mm, a current-gain cutoff frequency (fT) of 112 GHz, and a maximum oscillation frequency (fmax) of 215 GHz. To our knowledge, these are the highest gm , fT, and fmax values reported to date for an E-mode GaN HFET.

Reduced Sensitivity to Charge Noise in Semiconductor Spin Qubits via Symmetric Operation.

High data rate E-band (71 GHz- 76 GHz, 81 GHz - 86 GHz, 92 GHz - 95 GHz) communication systems will benefit from power amplifiers that are more than twice as powerful than commercially available GaAs pHEMT MMICs. We report development of three stage GaN MMIC power amplifiers for E-band radio applications that produce 500 mW of saturated output power in CW mode and have > 12 dB of associated power gain. The output power density from 300 mum output gate width GaN MMICs is seven times higher than the power density of commercially available GaAs pHEMT MMICs in this frequency range.