Al 0 26 Ga 0 74 N-GaN heterojunction field-effect transistors were grown by metal-organic chemical vapor deposition on high-resistivity 100-mm Si (111) substrates. Van der Pauw sheet resistance of the two-dimensional electron gas was 300 square with a standard deviation of 10 square.Maximum drain current density of 1 A/mm was achieved with a three-terminal breakdown voltage of 200 V. The cutoff frequency and maximum frequency of oscillation were 18 and 31 GHz, respectively, for 0.7-m gate-length devices. When biased at 50 V, a 2.14-GHz continuous wave power density of 12 W/mm was achieved with associated large-signal gain of 15.3 dB and a power-added efficiency of 52.7%. This is the highest power density ever reported from a GaN-based device grown on a silicon substrate, and is competitive with the best results obtained from conventional device designs on any substrate.Index Terms-GaN, heterojunction field-effect transistor (HFET), high electron mobility transistor (HEMT), power density, silicon.

The reducing inhibition of interfacial electron transfer and the resulting impact on the catalytic current of bilirubin oxidase (BOx) biocathodes is explored. Polymer‐coated multi‐wall carbon nanotubes (MWNTs) are modified with tethering and orientating agents to provide stable immobilization and efficient enzyme orientation. 1‐pyrenebutanoic acid, succinimidyl ester (PBSE) is used as a cross‐linker. A BOx natural substrate, bilirubin, and its artificial analogues are explored as orientating agents. It is established that bilirubin/PBSE‐modified BOx cathodes show approximately 0.4‐ and 3.2‐fold increases in the current density compared to cathodes modified separately with either PBSE or bilirubin, respectively. In subsequent experiments, the incorporation of PBSE and 2,5‐dimethyl‐1‐phenyl‐1H‐pyrrole‐3‐carbaldehyde, a functional analogue of bilirubin, into the MWNT matrix results in a further 2–2.5‐fold increase in the generated current density compared to the hybrid bilirubin/PBSE‐modified cathode, which is, therefore, 20 times higher than the unmodified BOx cathode. This significant enhancement in the performance of the cathode is attributed to the concomitant covalent attachment and proper orientation of BOx, which leads to improved enzyme/electrode interactions.

An NAD+-dependent enzymatic sensor with biofuel cell power source system for non-invasive monitoring of lactate in sweat was designed, developed, and tested. The sensor component, based on lactate dehydrogenase, showed linear current response with increasing lactate concentrations with limits of detection from 5 to 100 mM lactate and sensitivity of 0.2 µA.mM−1 in the presence of target analyte. In addition to the sensor patch a power source was also designed, developed and tested. The power source was a biofuel cell designed to oxidize glucose via glucose oxidase. The biofuel cell showed excellent performance, achieving over 80 mA at 0.4 V (16 mW) in a footprint of 3.5 × 3.5 × 0.7 cm. Furthermore, in order to couple the sensor to the power source, system electronic components were designed and fabricated. These consisted of an energy harvester (EH) and a micropotentiostat (MP). The EH was employed for harvesting power provided by the biofuel cell as well as up-converting the voltage to 3.0 V needed for the operation of the MP. The sensor was attached to MP for chronoamperometric detection of lactate. The Sensor Patch System was demonstrated under laboratory conditions.

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The degradation of 36mm AlGaN/GaN HFETs-on-Si under DC stress conditions has been studied on a large number of nominally identical devices that were chosen randomly across a production process. A common and primary degradation phenomenon was observed in the devices. A combination of electrical and physical analysis was used to identify a possible failure mechanism related to the Ni/Au Schottky gate diode that appears to explain the degradation of the FET. Based on the analysis, a gate anneal step was added into the fabrication process of AlGaN/GaN HFETs-on-Si. Nominal devices processed using a gate anneal showed (a) a modified gate metal-semiconductor interface (b) forward diode characteristics that are unchanged upon stress and (c) improvement in overall reliability relative to control devices.