D. Becher

Activation studies of low-dose Si implants in gallium nitride

The implantation of Si ions into undoped high-resistivity GaN films is of interest for the realization of high-performance digital and monolithic microwave integrated circuits. We report the effect of postimplant annealing conditions on the electrical, optical, and surface morphology of Si ion-implanted GaN films. We demonstrate high activation efficiencies for low-dose Si implants into unintentionally doped GaN/sapphire heteroepitaxial films. The Si ions were implanted through an epitaxial AlN cap layer at 100 keV and a dose ∼5×1014 cm−2. Samples were subsequently annealed in an open-tube furnace for various times and temperatures. The postanneal electrical activation is correlated with the surface morphology of the film after annealing. The samples annealed at 1150 °C in N2 for 5 min. exhibited a smooth surface morphology and a sheet electron concentration ns∼6.8×1013 cm−2.

Direct ion-implanted 0.12 μm GaAs MESFET with f/sub t/ of 121 GHz and f/sub max/ of 160 GHz

An 0.12 /spl mu/m gate length direct ion-implanted GaAs MESFET exhibiting excellent DC and microwave characteristics has been developed. By using a shallow implant schedule to form a highly-doped channel and an AsH/sub 3/ overpressure annealing system to optimize the shallow dopant profile, the GaAs MESFET performance was further improved. Peak transconductance of 500 mS/mm was obtained at I/sub ds/=380 mA/mm. A noise figure of 0.9 dB with associated gain of 8.9 dB were achieved at 18 GHz. The current gain cutoff frequency f/sub max/ of 160 GHz indicates the suitability of this 0.12 /spl mu/m T-gate device for millimeter-wave IC applications.

Improved Performance of AlGaN/GaN Heterojunction Field-Effect Transistors Using Delta Doping and a Binary Barrier

The improved performance of AlGaN/GaN heterojunction field-effect transistors using a delta-doping approach along with an AlN binary barrier is reported. Low-pressure metalorganic chemical vapor deposition was used to grow the epitaxial heterostructures on semi-insulating SiC substrates. The maximum carrier mobility of µ=1,066 cm2/V-s and sheet carrier density of ns~2.30×1013 cm-2 yields a large nsµ product of 2.45×1016 V-s. Devices with 0.15 µm gate lengths exhibited a maximum current density of IDSmax=1.82 A/mm (at VG=+1 V) and a peak transconductance of gm=331 mS/mm. Furthermore, fT~55 GHz and fmax~115 GHz were measured.

Low-cost 38 and 77 GHz CPW MMICs using ion-implanted GaAs MESFETs

Oscillators, amplifiers, and frequency doublers at 38 and 77 GHz have been fabricated using direct ion-implanted GaAs MESFETs and CPW. The 38-GHz VCO delivers 12 d8m of power and the 77-GHz amplifier has 7.5 dB of gain. The various circuit results demonstrate that the direct ion-implanted GaAs MESFET process is a low-cost alternative to more expensive epitaxial device technologies for a wide variety of existing and emerging millimeter-wave circuit applications.

DEVELOPMENT OF BROADBAND LOW ACTUATION VOLTAGE RF MEM SWITCHES

Low insertion loss, high isolation RF MEM switches have been thought of as one of the most attractive devices for space-based reconfigurable antenna and integrated circuit applications. Many RF MEMS switch topologies have been reported and they all show superior RF characteristics compared to semiconductor-based counterparts. At the University of Illinois, we developed state-of-the-art broadband low-voltage RF MEM switches using cantilever and hinged topologies. We demonstrated promising sub-10 volts operation for both switch topologies.The switches have an insertion loss of less than 0:1 dB, and an isolation of better than 25 dB over the frequency range from 0.25 to 40 GHz. The RF Model of the MEM switch was also established. The low voltage RF MEM switches will provide a solution for low voltage and highly linear switching methods for the next generation of broadband RF, microwave, and millimeter-wave circuits.

Low-cost GaAs MESFET and InP HFET technologies for 40-Gb/s OEICs

40 Gb/s are expected to become the future standard fiber- optic operating speed for the data communication and telecommunication systems. High performance and low cost technologies are required to lower the system cost, yet maintain the overall performance. In this paper, a state of the art ion implant GaAs MESFET and a simple layer structure InP/InGaAs doped channel HFET were described, compared and proposed for 40 Gb/s OEICs. We have developed 0.10 (mu) M gate direct ion implanted GaAs MESFET process with current cutoff frequency (ft) of 120GHz which is the highest reported ft for 0.1 micrometers gate MESFET device. Bas4ed on this result, we believe a low cost solution of ion implant GaAs MESFET with ft greater than 200GHz process is available in the n ear future with 0.05micrometers gate. The 0.14 micrometers InP/InGaAs doped channel HFET has ft of 188GHz, which is the highest reported doped channel HFET device. The measured device performance of both devices are described in the paper. Compared to the epitaxial device, the ion implant MESFET has the significant advantage in the low cost solution of 40 Gb/s OEIC. The doped channel HFET provides superior performance than MESFET, yet it needs only 5 epitaxial layers which provide advantage over HEMT device. 40Gb/s OEIC receiver was studied and designed using HFET HSPICE model. The simulation shows the circuit has bandwidth of greater than 30GHz with greater than 40 dB ohms gain which make it suitable for 40 Gb/s application. Using this circuit, a 1 by 4 OEIC receiver array in a wavelength division multiplexing system will have overall data rate of 160 Gb/s.