Kopin Corporation (United States)

To be widely adopted for consumers, smart headsets should be fashionable, comfortable, and provide useful applications. This paper will focus on the technologies, including microdisplays, small optics, high energy‐density batteries and reliable voice interface, which are necessary for making good consumer smart headsets but not available from smartphones. Two examples of consumer smart eyewear design are shown.

We have investigated the effect of proton irradiation on reliability of InAlN/GaN high electron mobility transistors (HEMTs). Devices were subjected to 5-15 MeV proton irradiations with a fixed dose of 5 × 10 15 cm -2 , or to a different doses of 2 × 10 11 , 5 × 10 13 or 2 × 10 15 cm -2 of protons at a fixed energy of 5 MeV. During off-state electrical stressing, the typical critical voltage for un-irradiated devices was 45 to 55 V. By sharp contrast, no critical voltage was detected for proton irradiated HEMTs up to 100 V, which was instrument-limited. After electrical stressing, no degradation was observed for the drain or gate current-voltage characteristics of the proton-irradiated HEMTs. However, the drain current decreased ~12%, and the reverse bias gate leakage current increased more than two orders of magnitude for un-irradiated HEMTs as a result of electrical stressing.

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Lattice-matched depletion-mode InAlN/AlN/GaN high-electron mobility transistors (HEMTs) on a SiC substrate were fabricated, for the first time, with a dielectric-free passivation (DFP) process in which the device access region was treated by O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar plasma. Similar to dielectric passivation using SiN and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , the plasma treatment can effectively shorten the gate-length extension. As a result, the current gain cutoff frequency fT of a 60-nm rectangular-gate HEMT increased from 125 to 210 GHz after the plasma DFP; this RF performance is among the highest reported fT for GaN-based HEMTs. The device showed a dc drain current density of 2.1 A/mm and a peak extrinsic transconductance of 487 mS/mm after DFP. The Lg-fTproduct of 12.6 GHz ·μm is among the highest reported for a gate-physical-length-to-barrier-thickness aspect ratio of 5.6. Small gate lag and drain lag are observed in pulsed I-V measurements with a 300-ns pulsewidth.

GaN-based high electron mobility transistors (HEMTs) have been developed for high-temperature, high-frequency and high-power applications. To improve the transistor speed, various techniques have been explored in addition to scaling down the gate length and top barrier thickness: ultrathin SiN passivation to reduce access resistance and parasitic capacitances [1]; re-grown ohmic contacts and self-alignment to minimize access resistances [2, 3]; O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> plasma treatment in the gate region prior to the metal deposition to suppress rf transconductance collapse [4]; and dielectric-free passivation (DFP) by a O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -containing plasma treatment in the access region to shorten the gate extension in InAlN HEMTs [5]. Here we report a comparative study on the impact of various plasma treatments in the access region (DFP) as well as under the gate for InAl(Ga)N barrier HEMTs, and propose a model for the observed f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> improvement.

By replacing the commonly used Ni/Au gate metallization with Pt/Ti/Au, the critical voltage for degradation of AlGaN/GaN High Electron Mobility Transistors (HEMTs) during off-state biasing stress was significantly increased. The typical critical voltage for the HEMTs with Ni/Au gate metallization was around -55V. By sharp contrast, no critical voltage was observed for the HEMTs with Pt/Ti/Au gate metallization, even up -100V, which was the instrumental limitation in this experiment. Both Schottky forward and reverse gate characteristics of the Ni/Au degraded once the gate voltage passed the critical voltage of -55V. There was no degradation exhibited for the HEMTs with Pt/Ti/Au gate metallization.

Nitrogen ion-implanted AlGaN/GaN high electron mobility transistor structures showed an isolation blocking voltage of 900 V with a leakage current at 1 μA/mm across an implanted isolation-gap of 10 μm between two Ohmic pads. The effect of implanted gap distance (1.7, 5, or 10 μm) between two Ohmic contact pads was evaluated. The isolation current density was determined to be solely dependent on the applied field between the contact pads. A model using a combination of resistive current and Poole–Frenkel current is consistent with the experimental data. The resistance of the isolation implantation region significantly decreased after the sample was annealed at temperatures above 600 °C.

Nitride semiconductors possess a number of unique material properties applicable to energy harvesting photovoltaic devices, including a large range of energy gaps, superior radiation resistance, and tolerance to high temperatures. We present here our experimental results related to the self-assembled InN quantum dots formed on Si substrates. We have been successful at synthesizing InN quantum dots using the metal-organic chemical vapor deposition (MOCVD) process. We demonstrate the synthesis of a high density of InN dots exhibiting excellent structural and optical properties. An unprecedented range of absorption energies, ranging from the infrared to the ultraviolet, can be obtained by embedding InN-based quantum dots in a wide band gap GaN barrier. The combination of energy-gaps accessible to III-V nitride materials may be used to reap the benefits of advance quantum dot device concepts involving hot carrier effects or multiple carrier generation processes.