Showing papers by "Bumman Kim published in 1985"

Process for forming a T-shaped gate structure

Abstract: Using the present invention, a gate for a MESFET may be fabricated having a minimum gate length while having a low resistance gate. In addition, the present invention provides a method for forming a gate and gate recess which are perfectly aligned which is the optimal structure for high frequency power MESFETs. A two layer masking layer is fabricated having a first layer which may be etched uniformly and a second layer of lithographic material which may be photolithographic material such as AZ resist. A gate opening is patterned in the photoresist material and a metal such as gold is deposited by evaporation from acute angles on opposite sides of the gate opening in the resist. The deposited metal serves as a mask which covers all but a very small portion of the opening in the photoresist. The silicon nitride layer is then etched to form a gate opening and gate recess. Gate contact metal is then deposited in the opening thus formed and the nitride, photoresist and gold layers are removed, lifting off a portion of the gate metal layer thus leaving a T-shaped gate which provides a minimum length at the channel gate interface and provides a low gate resistance.

110 GHz GaAs FET oscillator

Abstract: A W-band GaAs FET oscillator has been demonstrated for the first time A 75 μm gate width device with sub-half-micrometre (02 μm) electron-beam defined gates was used as a common-gate oscillator for operation in the 70 to 110 GHz frequency range The highest oscillation frequency achieved was 110 GHz

AlGaAs/GaAs Heterojunction bipolar power transistors

Abstract: An AlGaAs/GaAs heterojunction bipolar transistor with a total emitter periphery of 320 µm has been developed for power amplifier applications. For the base contact, Zn diffusion was used to convert the n-type emitter material into p-type with a doping of ∼1.0 × 1020 cm‾3. Because of the highly doped layer, contact resistivity was extremely low (5 × 10‾7 Ωcm2). At 3 GHz, a CW output power of 320 mW with 7 dB gain and 30% power-added efficiency was obtained. Under pulsed operation, the output power increased to 500 mW with 6 dB gain and 40% power-added efficiency. With further device structure optimisations, the power performance of heterojunction bipolar transistors is expected to rival, or even surpass, that of the GaAs MESFETs.

Millimeter-wave GaAs FET's prepared by MBE

Abstract: GaAs MESFET's suitable for operation in the millimeter-wave frequency range have been developed. These devices feature electron-beam-defined sub-half-micrometer gates with MBE grown materials. With an active-layer doping of 6 × 1017/cm3, an extrinsic transconductance of 330 mS/mm was obtained. A 75-µm gate-width device has achieved a gain of 13, 9.5, and 6.5 dB at 35, 44, and 60 GHz, respectively.

Monolithic GaAs Dual-Gate FET Variable Power Amplifier Module

Abstract: The design, fabrication, and microwave performance of a monolithic four-stage GaAs dual-gate FET amplifier are described. A linear gain of 23 dB with 250 mW output power has been measured at 18 GHz. The highest power obtained was 500 mW with 21 dB gain at the same frequency. By varying the second gate bias voltage, a dynamic gain control range of more than 60 dB has been observed. The chip size is 6.45mm x 2.1mm x 0.1mm.

High Power Distributed Amplifier Using MBE Synthesized Material

Abstract: The main limitations of the output power of a distributed amplifier are the gate line loss and the gate-to-drain breakdown voltage. A novel circuit concept to reduce the gate loss using series capacitors on the gate feeding lines has been implemented. The device breakdown voltage has been improved by using an MBE grown material with two layers (low doped gate buffer layer and usual active layer). A monolithic GaAs distributed amplifier using 6 x 300 µm FETs has achieved an output power of 800 mW with 4dB gain. The power added efficiency was about 15%.