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     

Millimeter-wave ion-implanted gradedInxGa1-xAs MESFETs grown by MOCVD

The authors present the fabrication and characterization of ion-implanted graded In_xGa_1-xAs/GaAs MESFETs. The In_xGa_1-xAs layers are grown on GaAs substrates by MOCVD (metal-organic chemical vapor deposition) with InAs concentration graded from 15% at the substrate to 0% at the surface. 0.5-μm gate MESFETs are fabricated on these wafers using silicon ion implantation. In addition to improved Schottky contact, the graded In_xGa _1-xAs MESFET achieves maximum extrinsic transconductance of 460 mS/mm and a current-gain cutoff frequency f_t of 61 GHz, which is the highest ever reported for a 0.5-μm gate MESFET. In comparison, In_0.1Ga_0.9As MESFETs fabricated with the same processing technique show an f_t of 55 GHz     

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     

Microwave performance of GaAs-on-Si MESFETs with Si buffer layers

The incorporation of silicon-buffer layers is shown to be critical in attaining optimized microwave performance for GaAs on silicon MESFETs. A current gain cutoff frequency (f_t) of 18 GHz and maximum power cutoff frequency (f_max) of 30 GHz is reported for relaxed geometry devices. The low parasitic capacitance and excellent device isolation make this structure suitable for monolithic integration     

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     

MOCVD-grown 0.25-μm MESFET's using tertiary butyl arsine as thearsenic source

High-performance 0.25-μm-gate MESFETs on MOCVD-grown epitaxial structure have been fabricated using tertiary butyl arsine (TBA) as the arsenic source. TBA, a liquid-phase organometallic arsenic compound, is a promising alternate arsenic source due to its lower vapor pressure, which makes it safer to handle than arsine. DC characterizations show that the extrinsic peak transconductance is 508 mS/mm. From on-wafer S-parameter measurements, the MESFETs show a current-gain cutoff frequency of 55 GHz and a maximum-available-gain cutoff frequency of 93 GHz. These results represent the best results reported for MOCVD-grown MESFETs using a TBA source and compare favorably with the previously reported f_t of 40 GHz for molecular beam epitaxy (MBE)-grown MESFETs     

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     

Current-gain cutoff frequency comparison of InGaAs HEMTs

The current-gain cutoff frequency performance of pseudomorphic InGaAs/AlGaAs (20% InAs composition) high-electron-mobility transistors (HEMTs) on GaAs is compared to that of lattice-matched InGaAs/InAlAs HEMTs on InP. The current-gain cutoff frequency (f_t) characteristics as a function of gate length (L_g) indicate that the f_t-L_g product of ~26 GHz-μm in InGaAs/InAlAs HEMTs is 23% higher than that of ~21 GHz-μm in InGaAs/AlGaAs HEMTs. The performance of InGaAs/AlGaAs HEMTs is also 46% higher than that of conventional GaAs/AlGaAs HEMTs (~18 GHz-μm). These data are very useful in improving the device performance of HEMTs for a given gate length     

A high-performance lateral bipolar transistor fabricated on SIMOX

Double-diffused, lateral n-p-n bipolar transistors were fabricated in a simple CMOS-like process using SIMOX silicon-on-insulator (SOI) substrates. Excellent device characteristics were achieved, with peak h_FE=120, BV_CEO=10 V, and peak f_t=4.5 GHz. The f_t versus BV _CEO trade-off was studied as a function of n ^- collector width. f_t>25 GHz is predicted for this structure with an improved device layout and optimized basewidth. This process may be easily extended in order to fabricate complementary BJTs in a C-BiCMOS thin-film SOI technology     

On the speed and noise performance of direct ion-implanted GaAsMESFETs

Recent advances in high-speed and ultra-low-noise performance of GaAs MESFETs are reviewed. Experimental results showing that the current gain cutoff frequency and noise figure achieved by direct ion-implanted GaAs MESFETs are equal to or better than those achieved by GaAs HEMTs are presented. Detailed cryogenic-temperature microwave measurements of F_t on HEMTs and MESFETs are reported, showing a similar dependence of the effective velocity with temperature. It is concluded that the transport properties of the high electron mobility in the two-dimensional electron gas in HEMTs have been misinterpreted for high-speed device operation, and that the high-field velocity is the most important parameter for high-speed device operation. It is the fundamental Γ-L valley separation of the material and the associated effectiveness, either GaAs or InGaAs, that limit the high-field velocity and thus the speed of the devices     

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     

Characterization of ultra-high-speed pseudomorphic AlGaAs/InGaAs(on GaAs) MODFETs

The authors report a detailed characterization of ultrahigh-speed pseudomorphic AlGaAs/InGaAs (on GaAs) modulation-doped field-effect transistors (MODFETs) with emphasis on the device switching characteristics. The nominal 0.1-μm gate-length device exhibit a current gain cutoff frequency (f_t) as high as 152 GHz. This value of f_t corresponds to a total delay of approximately 1.0 ps and is attributed to the optimization of layer structure, device layout, and fabrication process. It is shown that the electron transit time in these very short gate-length devices still accounts for approximately 60% of the total delay, and, as a result, significant improvements in switching speed are possible with further reductions of gate length. The results reported clearly demonstrate the potential of the pseudomorphic AlGaAs/InGaAs MODFET as an ultrahigh-speed device. Its excellent switching characteristics are attributed to the high saturation velocity (~2×10⁷ cm/s), 2DEG sheet density (2.5×10¹² cm^-2), and current drive capability (>200 mA/mm at the peak transconductance)     

Small-signal characteristics of n+-Ge gate AlGaAs/GaAsMISFET's

The small-signal characteristics have been clarified by S-parameter measurements and equivalent circuit modeling. A large intrinsic transconductance of 630 mS/mm and a maximum cutoff frequence f_T of 70 GHz have been achieved for a MISFET with a gate length of 0.4 μm. The average electron drift velocity in the channel, evaluated from the f_T, was as high as 1.7×10⁷ cm/s. In obtaining an equivalent-circuit model, a gate conductance parallel to the gate-source capacitance is introduced to take into account the gate forward current of normally-off FETs The gate conductance does not cause the f _T of the MISFET to deteriorate due to a small gate forward current at a large gate bias, in contrast to GaAs 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     

Si/a-Si:H heterojunction microwave bipolar transistors with cut-offfrequencies ft above 5 GHz

The fabrication of a silicon heterojunction microwave bipolar transistor with an n⁺ a-Si:H emitter is discussed, and experimental results are given. The device provides a base sheet resistance of 2 kΩ/□ a base width 0.1 μm, a maximum current gain of 21 (V_CE=6 V, I_c=15 mA), and an emitter Gummel number G _E of about 1.4×10¹⁴ Scm^-4. From the measured S parameters, a cutoff frequency f_t of 5.5 GHz and maximum oscillating frequency f_max of 7.5 GHz at V_CE=10 V, I_c=10 mA are obtained     

Electron space-charge effects on high-frequency performance ofAlGaAs/GaAs HBTs under high-current-density operation

The high-frequency characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) under high-current-density biasing condition are investigated in conjunction with the electron space charge in the collector depletion layer. A significant increase in cutoff frequency f_t and maximum oscillation frequency f_max at the early stage of the base push-out was observed in HBTs with a lightly doped n-type collector structure, and is attributed to the collector depletion layer widening and the enhancement of the velocity overshoot effect caused by the increasing electron density     

Microwave pnp AlGaAs/GaAs heterojunction bipolartransistor

The microwave performance of a pnp AlGaAs/GaAs heterojunction bipolar transistor was demonstrated for the first time. Common emitter current gains of 60 were obtained using MOCVD grown structures with 100 nm thick base layers and self-aligned emitter-base contacts. f_t and f_max values were 12 and 20 GHz respectively. Under common-base configuration, 8 dB gain was obtained at 10 GHz. Device performance was characterised under CW and pulsed conditions     

High drain current-voltage product of submicrometer-gateion-implanted GaAs MESFET's for millimeter-wave operation

Ion-implanted GaAs MESFETs with gate lengths of 0.3 and 0.5 μm have been fabricated using optical lithography. The devices with 0.3- and 0.5-μm gate lengths exhibit extrinsic transconductances, at zero gate bias, of 200 and 180 mS/mm at drain currents of 400 and 420 mA/mm, respectively. The gate-to-drain diode characteristics of these two different gate-length devices show similar breakdown voltages of 13-15 V. From S-parameter measurements, current-gain cutoff frequencies, f _ts, of 56 and 30 GHz are obtained for 0.3- and 0.5-μm gate-length devices, respectively. The high drain current-voltage product and the microwave performance indicate that ion-implanted technology has the potential to be used to manufacture power devices for millimeter-wave applications     

A broad-band amplifier using GaAs/GaAlAs heterojunction bipolartransistors

A compact wideband amplifier (or gain block) designed around a Darlington pair of GaAs/GaAlAs heterojunction bipolar transistors (HBTs) is discussed. This circuit has been fabricated by an ion-implanted process with a transistor f_t of 40 GHz. Two variants of the circuit gave either a 8.5-dB gain with a DC-to-5-GHz 3-dB bandwidth or a 13-dB gain with a DC-to-3-GHz bandwidth. These amplifiers gave 11.8- and 18.3-dBm output, respectively, at 1-dB gain compression     

0.33-μm gate-length millimeter-wave InP-channel HEMTs with highf1 and fmax

The fabrication of 0.33-μm gate-length AlInAs/InP high electron mobility transistors (HEMTs) is reported. These InP-channel devices have f_t values as high as 76 GHz, f_max values of 146 GHz, and maximum stable gains of 16.8, 14, and 12 dB at 10, 18, and 30 GHz, respectively. The extrinsic DC transconductances are as high as 610 mS/mm; with drain-source breakdown voltages exceeding 10 V. The effective electron velocity in the InP channel is estimated to be at least 1.8×10⁷ cm/s, while the f_tL_g product is 29 GHz-μm. These results are comparable to the best reported results for similar InGaAs-channel devices