Quarter-micrometer gate ion-implanted GaAs MESFET's with an f1 of 126 GHz

The fabrication and characterization of a 0.25-μm-gate, ion-implanted GaAs MESFET with a maximum current-gain cutoff frequency f_t of 126 GHz is reported. Extrapolation of current gains from bias-dependent S-parameters at 70-100% of I _dss yields f₁'s of 108-126 GHz. It is projected that an f₁ of 320 GHz is achievable with 0.1-μm-gate GaAs MESFETs. This demonstration of f₁'s over 100 GHz with practical 0.25-μm gate length substantially advances the high-frequency operation limits of short-gate GaAs MESFETs     

High-performance In0.08Ga0.92As MESFETs onGaAs(100) substrates

In_0.08Ga_0.92As MESFETs were grown in GaAs (100) substrates by molecular beam epitaxy (MBE). The structure comprised an undoped compositionally graded In_xGa_1-x As buffer layer, an In_0.08Ga_0.92As active layer, and an n⁺-In_0.08Ga_0.92As cap layer. FETs with 50-μm width and 0.4-μm gate length were fabricated using the standard processing technique. The best device showed a maximum current density of 700 mA/mm and a transconductance of 400 mS/mm. The transconductance is extremely high for the doping level used and is comparable to that of a 0.25-μm gate GaAs MESFET with an active layer doped to 10¹⁸ cm^-3. The current-gain cutoff frequency was 36 GHz and the power-gain cutoff frequency was 65 GHz. The current gain cutoff frequency is comparable to that of a 0.25-μm gate GaAs MESFET     

Ultrahigh-frequency performance of submicrometer-gate ion-implantedGaAs MESFETs

A study of the high-frequency performance of short-gate ion-implanted GaAs MESFETs with gate lengths of 0.3 and 0.5 μm is discussed. Excellent DC and microwave performance have been achieved with an emphasis on the reduction of effective gate length during device fabrication. From f_t of 83 and 48 GHz for 0.3-0.5-μm gate devices, respectively, an electron velocity of 1.5×10⁷ cm/s is estimated. An f_t of 240 GHz is also projected for a 0.1-μm-gate GaAs MESFET. These experimental results are believed to be comparable to those of the best HEMTs (high-electron-mobility transistors) reported and higher than those generally accepted for MESFETs     

0.25-μm gate millimeter-wave ion-implanted GaAs MESFETs

Quarter-micrometer gated ion-implanted GaAs MESFETs which demonstrate device performance comparable to AlGaAs/InGaAs pseudomorphic HEMTs (high-electron mobility transistors) have been successfully fabricated on 3-in-diameter GaAs substrates. The MESFETs show a peak extrinsic transconductance of 480 mS/mm with a high channel current of 720 mA/mm. From S-parameter measurements, the MESFETs show a peak current-gain cutoff frequency f_t of 68 GHz with an average f_t of 62 GHz across the wafer. The 0.25-μm gate MESFETs also exhibit a maximum-available-gain cutoff frequency f_t greater than 100 GHz. These results are the first demonstration of potential volume production of high-performance ion-implanted MESFETs for millimeter-wave application     

Highly lattice-mismatched In0.26Ga0.74As/GaAsMESFET's: impact of critical thickness on device performance

Fabrication of 0.25-μm-gate MESFETs directly on In_0.26 Ga_0.74As epitaxial layers which are much thicker than the pseudomorphic critical thickness is described. The InAs mole fraction is increased in the MESFET channel to 26%. Whether the device performance can be further improved without detrimental dislocation effects as the channel thickness exceeds the critical thickness considerably is investigated. Despite large lattice mismatch and high defect density, these devices show excellent microwave performance with an extrinsic f_t of 120 GHz. Bias-dependent S-parameters indicate that the In_0.26Ga_0.74As MESFET maintains excellent device performance down to very low drain current without showing any performance degradation due to misfit or threading dislocations     

High-performance millimeter-wave ion-implanted GaAs MESFETs

GaAs MESFETs (metal-epitaxial-semiconductor-field-effect transistors) with ion-implanted active channels have been fabricated on 3-in-diameter GaAs substrates which demonstrate device performance comparable with that of AlGaAs/InGaAs pseudomorphic HEMT (high-electron-mobility transistor) devices. Implanted MESFETs with 0.5-μm gate lengths exhibit an extrinsic transconductance of 350 mS/mm. From S-parameter measurements, a current-gain cutoff frequency f₁ of 48 GHz and a maximum-available-gain cutoff frequency f_max greater than 100 GHz are achieved. These results clearly demonstrate the suitability of ion-implanted MESFET technology for millimeter-wave discrete device, high-density digital, and monolithic microwave and millimeter-wave IC applications     

In0.52Al0.48As/InxGa1-xAs (0.53⩽x⩽0.70) lattice-matched and strainedheterostructure insulated-gate FETs

The DC and microwave properties of In_0.52Al_0.48 Al/In_xGa_1-xAs (0.53⩽x⩽0.70) heterostructure insulated gate field-effect transistors (HIGFETs) with a quantum well channel design are presented. DC and microwave transconductances (g_m) are enhanced as the In content is increased in the InGaAs channel. An intrinsic microwave g _m value of 428 mS/mm and a K-factor of 1140 mS/mm-V have been obtained for 1.0-μm gate length with the 65% In channel devices. The sheet charge density, drift mobility, transconductance, current-gain cutoff frequency (f_T), and maximum oscillation frequency (f _max) all show a continuous improvement up to 65% In content ( f_T=22.5 GHz with 53% and f_T=27 GHz with 65% In; the corresponding f_max change is from 6.5 to 8 GHz). The device performance degrades as the In content is increased to 70%. DC and microwave characteristics show the presence of negative differential resistance (NDR) up to 2.7 GHz     

Doubly strainedIn0.41Al0.59As/n+-In0.65Ga0.35As HFET with high breakdown voltage

An In_0.41Al_0.59As/n⁺-In_0.65 Ga_0.35As HFET on InP was designed and fabricated, using the following methodology to enhance device breakdown: a quantum-well channel to introduce electron quantization and increase the effective channel bandgap, a strained In_0.41Al_0.59As insulator, and the elimination of parasitic mesa-sidewall gate leakage. The In_0.65Ga_0.35As channel is optimally doped to N_D=6×10¹⁸ cm^-3. The resulting device (L_g=1.9 μm, W_g =200 μm) has f_t=14.9 GHz, f_max in the range of 85 to 101 GHz, MSG=17.6 dB at 12 GHz V_B=12.8 V, and I_D(max)=302 mA/mm. This structure offers the promise of high-voltage applications at high frequencies on InP     

Low-temperature microwave characteristics of pseudomorphic InxGa1-xAs/In0.52Al0.48Asmodulation-doped field-effect transistors

Low-temperature microwave measurements of both lattice-matched and pseudomorphic In_xGa_1-xAs/In_0.48As (x=0.53, 0.60, and 0.70) channel MODFETs on InP substrates were carried out in a cryogenic measurement system. The measurements were done in the temperature range of 77 to 300 K and in the frequency range of 0.5 to 11.0 GHz at different bias conditions. The cutoff frequency ( f_T) for the In_xGa_1-xAs/In_0.52Al_0.48As MODFETs improved from 22 to 29 GHz, 29 to 38 GHz, and 39 to 51 GHz, for x=0.53, 0.60, and 0.70, respectively, as the temperature was lowered from 300 to 77 K, which is approximately a 31% increase at each composition. No degradations were observed in device performance. These results indicate an excellent potential of the pseudomorphic devices at low temperatures     

60-GHz noise performance of ion-implanted InxGa1-xAs MESFET's

The authors report the 60-GHz noise performance of low-noise ion-implanted In_xGa_1-xAs MESFETs with 0.25 μm T-shaped gates and amplifiers using these devices. The device noise figure was 2.8 dB with an associated gain of 5.6 dB at 60 GHz. A hybrid two-state amplifier using these ion-implanted In_xGa_1-x As MESFETs achieved a noise figure of 4.6 dB with an associated gain of 10.1 dB at 60 GHz. When this amplifier was biased at 100% I _dss, it achieved 11.5-dB gain at 60 GHz. These results, achieved using low-cost ion-implantation techniques, are the best reported noise figures for ion-implanted MESFETs     

Gate-length dependence of DC and microwave properties ofsubmicrometer In0.53Ga0.47As HIGFETs

In_0.52Al_0.48As/In_0.53Ga_0.47 As/InP heterostructure insulated-gate field-effect transistors (HIGFETs) with gate lengths from 1.1 and 0.3 μm have been fabricated, and their electrical performance is characterized at DC and microwave frequencies. The refractory-gate self-aligned process, applied to devices with In_0.53Ga_0.47As channels, yields an unprecedented combination of very-high speed and excellent uniformity. HIGFETs with L_g=0.6 μm showed average peak transconductance g_m of 528 mS/mm and unity-current-gain cutoff frequency f_t of 50 GHz. The uniformity of g_m was better than 1%, and the voltage of the g_m peak was uniform to ±30 mV. HIGFETs with L_g=0.3 μm showed f₁ up to 63 GHz, but suffered from serious short-channel effect, due to excessive thickness of the InGaAs channel layer. A self-aligned technique for gate resistance reduction is shown to substantially improve microwave power gain     

An anisotype GaAs/InxGa1-xAs heterojunctionfield-effect transistor for digital logic applications

An anisotype heterojunction field-effect transistor (A-HJFET) for GaAs digital integrated circuit applications is proposed. A thin, highly doped, strained In_xGa_1-xAs (x⩽0.2) n-channel is employed for improved transconductance while a p⁺-GaAs cap is used to enhance the dynamic gate voltage range of the device. Prototype devices with 5-μm gate lengths show a maximum transconductance of 80 mS/mm at V_ds=2 V and a forward gate bias voltage of up to +2 V without significant leakage current     

Unstrained, modulation-doped, In0.3Ga0.7As/In0.29Al0.71As field-effect transistor grown on GaAssubstrate

The fabrication, structure, and properties of unstrained modulation-doped, 1-μm-long and 10-μm-wide gate, field effect transistors made of In_0.3Ga_0.7As/In_0.29As_0.71As heterojunctions grown on GaAs substrates using compositionally step-graded buffer layers are described. These devices have a transconductance of 335 mS/mm, f_max of 56 GHz, and a gate breakdown voltage of 23.5 V     

DC and microwave characteristics of InAlAs/InGaAssingle-quantum-well MODFETs with GaAs gate barriers

The design and performance of In_0.53Ga_0.47As/In_0.52Al_0.48 As modulation-doped field-effect transistors (MODFETs) have been optimized by incorporating a single In_0.53Ga_0.47As quantum-well channel and a thin strained GaAs gate barrier layer. These help to lower the output conductance and gate leakage current of the device, respectively. The DC performance of 1-μm-gate devices is characterized by extrinsic transconductances of 320 mS/mm at 300 K and 450 mS/mm at 77 K and a best value of f_T=35 GHz is derived from S-parameter measurements     

Ion-implanted GaAs/AlGaAs heterojunction FET's grown by MOCVD

The successful fabrication of an ion-implanted GaAs/AlGaAs heterojunction FET device is discussed. Half-micrometer gate-length FET devices are fabricated by ion implantation into GaAs/AlGa heterostructures grown by metalorganic chemical vapor deposition (MOCVD) on 3-in-diameter GaAs substrates. The FET device exhibits a maximum extrinsic transconductance of 280 mS/mm with reduced transconductance variation over 2 V of gate bias. Excellent microwave performance is achieved with an f_t of 40 GHz, which is comparable to results obtained from 0.25-μm gate GaAs MESFETs. The effects of ion implantation on the heterojunction and corresponding device characteristics are also discussed     

Integration of high-Q GaAs varactor diodes and 0.25 μmGaAs MESFET's for multifunction millimeter-wave monolithic circuitapplications

Two technologies are demonstrated whereby high-Q, vertical-structure, abrupt-junction varactor diodes are monolithically integrated with 0.25-μm GaAs MESFETs on semi-insulating GaAs substrates for multifunction millimeter-wave monolithic circuit applications. Diodes with various anode sizes have been realized with measured capacitance swings of >2.1:1 from 0 V to -4 V and series resistances of approximately 1 Ω. Diodes having a zero bias capacitance of 0.35 pF have Q's of >19000 (50 MHz) with -4 V applied to the anode. Under power bias conditions, the MESFETs have a measured gain of >6 dB at 35 GHz with extrapolated values for f _t and f_max of 32 GHz and 78 GHz, respectively. Using these technologies, a monolithic Ka-band voltage controlled oscillator (VCO) containing a varactor diode, a 0.25-μm GaAs MESFET, and the usual MMIC passive components has been built and tested. At around 31 GHz, the circuit has demonstrated 60-mW power output with 300 MHz of tuning bandwidth     

Characteristics including electron velocity overshoot for0.1-μm-gate-length GaAs SAINT MESFET's

Short-channel effects, substrate leakage current, and average electron velocity are investigated for 0.1-μm-gate-length GaAs MESFETs fabricated using the SAINT (self-aligned implantation for n⁺-layer technology) process. The threshold-voltage shift was scaled by the aspect ratio of the channel thickness to the gate length ( a/L_g). The substrate leakage current in a sub-quarter-micrometer MESFET is completely suppressed by the buried p layers and shallow n⁺-layers. The average electron velocity for 0.1- to 0.2-μm-gate-length FETs is estimated to be 3×10⁶ cm/s from the analysis of intrinsic FET parameters. This high value indicates electron velocity overshoot. Moreover, a very high f_T of 93.1 GHz has been attained by the 0.1-μm SAINT MESFET     

Scaling properties and short-channel effects in submicrometerAlGaAs/GaAs MODFET's: A Monte Carlo study

Scaling properties of n⁺-Al_xGa_1-xAs/GaAs MODFETs with submicrometer gate lengths (L_G=0.50 to 0.05 μm) are examined, using Monte Carlo methods. High-frequency performance of MODFETs can be improved by scaling the gate lengths, but various studies suggest that there exists a lower limit for the gate after which no improvement should be expected. The lower limit is determined here to be ≈0.10 μm. Devices with smaller gate lengths than 0.1 μm exhibit degraded transconductance (g_m), large shift in threshold voltage due to poor charge control in the channel, and a sharp reduction in output resistance (R_o). It is shown that the drain current saturation in MODFETs is not caused by the velocity saturation effect, but by channel pitch-off. Electron velocities calculated from Monte Carlo simulations and extracted from g_m and f_t measurements are reconciled     

A pseudomorphic AlGaAs/n+-InGaAs metal-insulator-dopedchannel FET for broad-band, large-signal applications

Molecular beam epitaxy (MBE)-grown L_g=1.7-μm pseudomorphic Al_0.38Ga_0.62As/n⁺-In_0.15Ga _0.85As metal-insulator-doped channel FETs (MIDFETs) are presented that display extremely broad plateaus in both f_T and f_max versus V_GS, with f_T sustaining 90% of its peak over a gate swing of 2.6 V. Drain current is highly linear with V_GS over this swing, reaching 514 mA/mm. No frequency dispersion in g _m up to 3 GHz was found, indicating the absence of electrically active traps in the undoped AlGaAs pseudoinsulator layer. These properties combine to make the pseudomorphic MIDFET highly suited to linear, large-signal, broadband applications     

8-element linear array monolithic p-i-n MODFET photoreceivers usingmolecular beam epitaxial regrowth

An 8-element linear array of single-stage integrating front-end photoreceivers using molecular beam epitaxial (MBE) regrowth was investigated. Each element consisted of a p-i-n In_0.53Ga_0.47As photodiode integrated with a selectively regrown pseudomorphic In_0.65Ga_0.35As/In_0.52Al_0.48 As MODFET. Cutoff frequencies of 1.0-μm discrete regrown MODFETs were f_t=24 GHz and f_max=50 GHz. Transconductance of the regrown MODFETs was as high as 495 mS/mm with a current density (I_ds) of 250 mA/mm. The 3-dB bandwidth of the photoreceiver was measured to be 1 GHz. The bit rate sensitivity at 1 Gb/s was -31.8 dBm for BER 10^-9 using 1.55 μm excitation for a photoreceiver with an anti-reflection coating. The single-stage amplifier exhibited up to 25 dB flatband gain of the photocurrent, and a two-stage amplifier was up to 31 dB of gain. Good uniformity between each photoreceiver element in the array was achieved. Electrical crosstalk between photoreceiver elements was estimated to be ~-34 dB