W. Patrick

Analytical bias dependent noise model for InP HEMT's

A practical device model for both high frequency small signal and noise behavior of InP-HEMTs depending on both gate and drain voltage has been developed. The model is based on the two-piece linear approximation using charge control and saturation velocity models. Combining large signal model and analytical expressions for the noise source parameter P, R, and C, an analytical bias-dependent noise model can be obtained. For implementation into high frequency simulation software, the exact calculated bias dependence was mathematically fitted by elementary functions. It could be shown that lowest noise is observed when the drain current for maximum gain is reduced to a third while the drain voltage is reduced to the start of the saturation region V/sub ds/=0.6 V. Modeling scaling effects of the noise behavior shows that lowest noise is observed for a gate width of 1/spl times/40 /spl mu/m. Multi-finger layouts are preferable for gate widths above 70 /spl mu/m. Furthermore it is shown, that the optimum width of each finger decreases with the number of fingers. >

Atomic force microscopy investigations of dry etched gate recesses for InGaAs/InAlAs‐based high‐electron‐mobility transistors using methane–hydrogen reactive ion etching

A methane–hydrogen (CH4/H2) reactive ion etching process has been developed for selective gate recess etching of lattice‐matched InGaAs/InAlAs/InP high‐electron‐mobility transistors without the need for additional ashing or annealing steps after dry etching. An atomic force microscope was used for accurate studies of the morphology of the etched 0.2 μm gate recess. We found that dry etching does not alter the surface roughness significantly for low methane concentrations. Direct current and microwave measurements showed uniform device parameters with a peak transconductance gmmax of 700 mS/mm and a unity current gain frequency ft of 170 GHz.

Reactive ion etch‐induced effects on 0.2 μm T‐gate In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobility transistors

The effect of CH4/H2 reactive ion etching on In0.52Al0.48As surfaces and In0.52Al0.48As/ In0.53Ga0.47As/InP heterostructure have been studied using Schottky diode, x‐ray photoelectron spectroscopy, and room temperature transport experiments. The application of CH4/H2 as a dry etch gas for the gate recess step in the fabrication of 0.2 μm T‐gate In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobility transistor has been explored. We show that while the room temperature mobility and the dc and high frequency performance of the dry etched devices are at least comparable to the wet etched ones, their microwave noise behaviours are extremely sensitive to dry etch‐induced defects.

Determination of the noise source parameters in AlInAs/GaInAs HEMT heterostructures based on measured noise temperature dependence on the electric field

The noise temperature dependence on the electric field in an AlInAs/GaInAs HEMT heterostructure has been measured. It was found that the dependence of the noise temperature on the electric field in GaAs MESFETs and in AlInAs/GaInAs HEMTs are remarkably different. For this reason a different model must be used for AlInAs/GaInAs HEMTs. Based on the measured noise temperature dependence on the electric field, am analytic noise model for the AlInAs/GaInAs HEMT has been developed. The noise source parameters were calculated and compared with extracted noise source parameters from noise measurements.<<ETX>>

Integrated coplanar mm-wave amplifier with gain control using a dual-gate InP HEMT

A variable gain mm-wave amplifier, based on InP HEMT devices, is demonstrated. The measured gain control range of 14 dB is the largest reported in the mm-wave range for a monolithically integrated variable gain amplifier. The two stage circuit consists of a single gate transistor and a dual-gate transistor. The circuit has a maximum gain of 22 dB at 44 GHz and a bandwidth of 14.6 GHz. The circuit was fabricated in coplanar technology.

Monolithic V-band high power and varactor tunable HEMT oscillators

The design, fabrication, and the measured results of V-band monolithically integrated fundamental oscillators are presented. The active device is a 0.2 /spl mu/m InP based HEMT with f/sub max/=200 GHz and f/sub t/=100 GHz. A basic V-band oscillator, a high power and a varactor tuned oscillator are compared. The resonance frequency of the basic oscillator is 54.333 GHz and the phase noise -70 dBc/Hz @ 1 MHz offset. The high power oscillator shows 83 dBm output power at 48 GHz For the varactor tunable oscillator an output power of 0 dBm at 63 GHz and a tuning range of 100 MHz are measured. The circuits were fabricated in coplanar technology.

Comparison and optimisation of different ohmic contact metallisations for InP-HEMT structures with doped and undoped cap-layers

A direct comparison was made between several ohmic contact metallisations using Ni, Ge and Au for InP based HEMT applications. HEMT structures with both doped and undoped GaInAs cap-layers were investigated. Ni-Ge-Au proved to be the most suitable contact for both structures. An optimum nickel thickness of 100 /spl Aring/ Ni followed by 500 /spl Aring/ Ge and 800 /spl Aring/ Au was found. The contact resistances of the optimised Ni-Ge-Au structure were as low as 0.09 /spl Omega/mm and relatively insensitive to anneal time and temperature and are therefore most suitable for IC fabrication. For applications where high anneal temperatures are required, Ge-Ni-Au ohmic contacts show the largest process window for the anneal temperature. Furthermore it is reported that the contact resistance is independent of the doping of the thin (50-100 /spl Aring/) cap-layer. This indicates that it is the bandgap and not the doping of the cap-layer, which determines the contact resistance to the HEMT structure.<<ETX>>

Frequency analysis of the kink effect in AlInAs/GaInAs HEMTs

A frequency analysis of the transconduction and output conduction of 0.25 /spl mu/m InP based HEMTs was carried out using S-parameter measurements down to 1 kHz. The advantage of this method is that very low frequency and hf performance is determined using a single measurement sequence. It has been shown that the kink effect in the output characteristics consists of two ranges of a reduced and an increased drain current. Additionally it was found, that while g/sub d,hf/ increases for more positive gate voltages, g/sub d,dc/ usually decreases. It has also been shown, that the dc measured transconductance g/sub m,dc/ is lower than g/sub m,hf/. This difference is increased for high drain voltages. The frequency analysis shows that g/sub m,dc/ is generally decreased at higher drain voltages. Finally, it has been shown that the dispersion output conduction can be up to the GHz range for high drain source voltages.

Influence of cap-layer doping on ohmic contacts for InP based hemt structures

Abstract Ohmic contacts to lattice matched InP based HEMT structures with both doped and undoped GaInAs cap-layers have been investigated. Contact resistances as low as 0.09 Ωmm were achieved using annealed NiGeAu ohmic contacts. It is reported that the contact resistance is independent of the doping of the thin (50–100 A) cap-layer. This indicates that it is the bandgap and not the doping of the cap-layer, which determines the contact resistance to the HEMT structure. Furthermore it was shown, that the contact resistance is reduced for lower sheet resistances of the 2DEG.

Passive, coplanar V-band HEMT mixer

A passive V-band mixer is presented which uses an InP HEMT for mixing. The measured minimum conversion loss is 10.3 dB (RF 61 GHz, LO 60 GHz) with an LO power of 6 dBm. The circuit was fabricated in coplanar technology.