Submillimeter-wave InP Gunn devices

Recent advances in design and technology signifi- cantly improved the performance of low-noise InP Gunn devices in oscillators first at -band (110–170 GHz) and then at -band (75–110 GHz) frequencies. More importantly, they next resulted in orders of magnitude higher RF output power levels above -band and operation in a second harmonic mode up to at least 325 GHz. Examples of the state-of-the-art performance are continuous-wave RF power levels of more than 30 mW at 193 GHz, more than 3.5 mW at 300 GHz, and more than 2 mW at 315 GHz. The dc power requirements of these oscillators compare favorably with those of RF sources driving frequency multiplier chains to reach the same output RF power levels and frequencies. Two different types of doping profiles, a graded profile and one with a doping notch at the cathode, are prime candidates for operation at submillimeter- wave frequencies. Generation of significant RF power levels from InP Gunn devices with these optimized doping profiles is predicted up to at least 500 GHz and the performance predictions for the two different types of doping profiles are compared

D-band (110-170 GHz) InP gunn devices

This paper reports on the development of InP Gunn sources for operation in the D-band (110-170 GHz). n+-n-n+ structures with flat doping as well as graded doping profiles have been considered. Oscillations were obtained at 108.3 GHz from a 1 [mu]m structure with a uniform n doping of 2.5 x 1016 cm-3. The CW RF output power was 33 mW. A 1 [mu]m graded structure with an n doping increasing linearly from 7.5 x 1015 to 2.0 x 1016 cm-3 has resulted in 20 mW at 120 GHz and 10 mW at 136 GHz. These results are believed to correspond to a fundamental mode operation and represent the state-of-the-art performance from InP Gunn devices at these frequencies. This improvement in performance is attributed in part to a processing technique based on the use of etch-stop layers and InGaAs cap layers. An etch-stop layer allows low-profile mesas (2-3 [mu]m) and InGaAs cap layers help reduce the contact resistance, thus minimizing series resistances in the device. In addition, a physical model based on the Monte Carlo method was developed to aid in the design of structures for high frequency operation. Experimental results obtained from a 1.7 [mu]m Gunn device operating at W-band frequencies were used to estimate appropriate InP material parameters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30504/1/0000133.pd

Ensemble Monte Carlo characterization of graded AlxGa1−xAs heterojunction barriers

Injection over and through heterojunction barriers is becoming increasingly more important in modern electronic devices. We consider the properties of graded AlxGa1−xAs heterojunction barriers using a self‐consistent ensemble Monte Carlo method. In this paper, we consider barriers with two doping levels, 1×1015 cm−3 and 1×1017 cm−3, and two barrier heights, 100 and 265 meV. The 100‐meV barrier resulted in small rectification at room temperature whereas the higher barrier exhibited considerable rectification. In both cases the structure with the lower doped barrier has resulted in a smaller current in both forward and reverse regions due to space‐charge effects. The energy and momentum distribution functions deviate from a Maxwellian distribution inside the barrier region and in general show two peaks: one is comprised mainly of electrons near equilibrium and the second arises mainly from ballistic electrons. The higher doped structure resulted in a faster electron relaxation toward equilibrium as a function of position because the electric field decreases rapidly in the barrier region.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70741/2/JAPIAU-68-3-1114-1.pd

Active two-terminal devices as local oscillators for low-noise receiver systems at submillimeter wave frequencies

The power capabilities of three different two-terminal devices, GaAs IMPATT diodes, InP Gunn devices and GaAs TUNNETT diodes are evaluated. Two different selective etching technologies have been employed to fabricate devices on either a diamond heat sink or an integral heat sink. The reported RF power levels in fundamental mode are 20 mW at 120 GHz and 15 mW at 135 GHz for D-band GaAs IMPATT diodes, 21 mW at 120 GHz, 17 mW at 133 GHz and 8 mW at 155 GHz for D-band InP Gunn devices and up to 35 mW around 103 GHz for W-band GaAs TUNNETT diodes. Typical de to RF conversion efficiencies range from 0.9% up to over 4.0%. In second harmonic mode power levels of 0.25 mW at 223 GHz were measured from TUNNETT diodes and 0.4 mW at 220 GHz from a Gunn device. Die Leistungsfähigkeit dreier verschiedener Zweipolbauelemente, GaAs-IMPATT-Dioden, InP-Gunn-Bauelemente und GaAs-TUNNETT-Dioden, wird untersucht. Zwei unterschiedliche Herstellungsverfahren mit selektivem Ätzen wurden eingesetzt, um Bauelemente auf einer Diamant- bzw. integrierten Wärmesenke herzustellen. Hochfrequenzausgangsleistungen von 20 mW bei 120 GHz und 15 mW bei 135 GHz wurden mit GaAs-IMPATT-Dioden für das D-Band erzielt, 21 mW bei 120 GHz, 17 mW bei 133 GHz und 8 mW bei 155 GHz mit InP-Gunn-Bauelementen für das D-Band und bis zu 35 mW um 103 GHz mit GaAs-TUNNETT-Dioden für das W-Band. Typische Hochfrequenzwirkungsgrade lagen zwischen 0,9% und über 4%. Bei der ersten Oberwelle wurden mit TUNNETT-Dioden HF-Leistungen von 0,25 mW bei 223 GHz gemessen und 0,4 mW bei 220 GHz mit einem Gunn-Bauelement.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46116/1/202_2005_Article_BF01574916.pd

A low-power low-data-rate neural recording system with adaptive spike detection

A design of small, low-power, low-data rate, wireless 32-channel neural recording system for small animal head-stage is presented. A neural pre-amplifier has low-input-referred-noise of 1.95 muVrms and consumes 53.6 muW. To enable digital telemetry with optimized bandwidth under size and power constraint for small-animal headstage, we propose to separately record spikes and local-field potentials. An adaptive spike detector using absolute value algorithm accompanied with 7th-order all-pass delay filter provides accurate on-chip acquisition of spike waveform in duration of 2 ms. A low-power 10-bit and 5-bit resolution A/D converters running at 22 Ksamples/s for active spikes and 200 samples/s for local field potential, respectively, can be integrated with the proposed system. Using adaptive bandwidth control, we achieve reduction of data-rate up to seven times which provides compatibility to 1 Mbps ultra low power Bluetooth technology. Total power consumption of single channel excluding ADCs is 109.58 muW in 3.3 V power supply