Monolithically integrated high-power broad-band RF switch based on III-N insulated gate transistors

We report on the high-performance monolithically integrated RF switch based on metal-oxide-semiconductor III-N heterostructure field-effect transistors (MOSHFETs). The radio frequency (RF) switch microwave monolithic integrated circuit (MMIC) consists of three submicron-gate MOSHFETs connected into /spl pi/-type configuration. In the 0-10 GHz frequency range, the insertion loss is less than 1dB and the isolation is better than 20 dB. The switching powers well exceed 20 W per 1mm of the active element width. The high performance parameters of the switch are achieved due to unique properties of III-nitride MOSHFET, which combines a low channel resistance and high breakdown voltage features of AlGaN/GaN HFETs and extremely low gate leakage currents, large gate voltage swing and low gate capacitance specific to insulated gate design. The combination of these parameters makes MOSHFETs excellent candidates for high-power switching. The experimental data obtained from the RF switch are in close agreement with the results of simulations.     

High-power operation of III-N MOSHFET RF switches

We describe a large-signal performance of novel high-power radio frequency (RF) switches based on III-nitride insulated gate metal-oxide semiconductor heterostructure field-effect transistors (MOSHFETs). The maximum switching powers for a single MOSHFET with only 1-mm gate width exceed 50W at 10GHz, more than an order of magnitude higher than those achievable using GaAs transistors. In the ON state, the highest powers are determined by the device peak drain currents, 1-2A/mm for the state-of-the art III-N MOSHFETs; in the OFF state their maximum powers are limited by the breakdown voltage, normally well above 100V. Our experimental data are in close agreement with large-signal simulations and the proposed simple analytical model. We also show that the insulating gate design allows for broader bandwidth and higher switching powers and better stability as compared to conventional Schottky gate transistors.     

S-band operation of SiC power MESFET with 20 W (4.4 W/mm) output power and 60% PAE

Previous efforts have revealed instabilities in standard SiC MESFET device electrical characteristics, which have been attributed to charged surface states. This work describes the use of an undoped "spacer" layer on top of a SiC MESFET to form a "buried-channel" structure where the active current carrying channel is removed from the surface. By using this approach, the induced surface traps are physically removed from the channel region, such that the depletion depth caused by the unneutralized surface states cannot reach the conductive channel. This results in minimal RF dispersion ("gate lag") and, thus, improved RF performance. Furthermore, the buried-channel approach provides for a relatively broad and uniform transconductance (G/sub m/) with gate bias (V/sub gs/), resulting in higher efficiency MESFETs with improved linearity and lower signal distortion. SiC MESFETs having 4.8-mm gate periphery were fabricated using this buried-channel structure and were measured to have an output power of 21 W (P/sub out//spl sim/4.4 W/mm), 62% power added efficiency, and 10.6 dB power gain at 3 GHz under pulse operation. When operated at continuous wave, similar 4.8-mm gate periphery SiC MESFETs produced 9.2 W output power (P/sub out//spl sim/2 W/mm), 40% PAE, and /spl sim/7 dB associated gain at 3 GHz.     

Stable CW operation of field-plated GaN-AlGaN MOSHFETs at 19 W/mm

We report for the first time the dc and radio frequency (RF) operation of a field-plated GaN-AlGaN metal-oxide-semiconductor heterostructure field effect transistor (MOSHFET). At 2 GHz and an RF output power level of 19 W/mm (drain bias 55 V), the device exhibited a remarkably stable operation for times in excess of 100 h. In contrast, a similar geometry HFET from the same wafer continuously degraded from 17 W/mm down to 14 W/mm within the first 20 h. We attribute the stable performance of the MOSHFET at high microwave powers to the extremely low gate-leakage currents and the current collapse-free operation resulting from the field-plated design.     

High-power microwave GaN/AlGaN HEMTs on semi-insulating siliconcarbide substrates

Record performance of high-power GaN/Al_0.14-Ga_0.86 N high-electron mobility transistors (HEMTs) fabricated on semi-insulating (SI) 4H-SiC substrates is reported. Devices of 0.125-0.25 mm gate periphery show high CW power densities between 5.3 and 6.9 W/mm, with a typical power-added efficiency (PAE) of 35.4% and an associated gain of 9.2 dB at 10 GHz. High-electron mobility transistors with 1.5-mm gate widths (12×125 μm), measured on-wafer, exhibit a total output power of 3.9 W CW (2.6 W/mm) at 10 GHz with a PAE of 29% and an associated gain of 10 dB at the -2 dB compression point. A 3-mm HEMT, packaged with a hybrid matching circuit, demonstrated 9.1 W CW at 7.4 GHz with a PAE of 29.6% and a gain of 7.1 dB. These data represent the highest power density, total power, and associated gain demonstrated for a III-nitride HEMT under RF drive     

DC and RF Characteristics of 0.15 pm Power Metamorphic HEMTs

DC and RF characteristics of 0.15 °m GaAs power metamorphic high electron mobility transistors (MHEMT) have been investigated. The 0.15 °m ° 100 °m MHEMT device shows a drain saturation current of 480 mA/mm, an extrinsic transconductance of 830 mS/mm, and a threshold voltage of ‐0.65 V. Uniformities of the threshold voltage and the maximum extrinsic transconductance across a 4‐inch wafer were 8.3% and 5.1%, respectively. The obtained cut‐off frequency and maximum frequency of oscillation are 141 GHz and 243 GHz, respectively. The 8 ° 50 °m MHEMT device shows 33.2% power‐added efficiency, an 18.1 dB power gain, and a 28.2 mW output power. A very low minimum noise figure of 0.79 dB and an associated gain of 10.56 dB at 26 GHz are obtained for the power MHEMT with an indium content of 53% in the InGaAs channel. This excellent noise characteristic is attributed to the drastic reduction of gate resistance by the T‐shaped gate with a wide head and improved device performance. This power MHEMT technology can be used toward 77 GHz band applications.     

High-power RF switching using III-nitride metal-oxide-semiconductor heterojunction capacitors

We propose and demonstrate a novel III-Nitride high-power robust RF switch using SiO/sub 2/-AlGaN-GaN metal-oxide-semiconductor heterojunction (MOSH) capacitors. A metal electrode deposited on the top of the SiO/sub 2/ layer and the low-resistivity two-dimensional electron gas (2DEG) channel at the AlGaN-GaN interface serve as the MOSH capacitor plates. Two "back-to-back" connected MOSH capacitors form a double MOSH (D-MOSH) RF switch thereby eliminating the need for ohmic contacts and also allowing fully self-aligned fabrication. The D-MOSH switch has a symmetrical /spl pi/-type capacitance-voltage characteristic with a static ON-OFF capacitance ratio greater than 20:1. The RF switch exhibits similar polarity independent sharp /spl pi/-type transmission bias curve. At 2GHz, a single-element multifinger D-MOSH switch shows isolation greater than 25 dB and insertion loss of 0.7 dB. The switching power exceeds 60 W/mm making the novel D-MOSH switch robust device for high-power high-temperature integrated electronics.     

VCO phase-noise improvement by gate-finger configuration of 0.13-/spl mu/m CMOS transistors

Using a standard logic process, 0.13-/spl mu/m RF CMOS devices with multifinger gate structure have been fabricated. The flicker noise and minimum noise figure characteristics have been investigated with different gate layout splits, where the device parasitic resistance is the determining factor in this issue. The stripe-shaped gate configuration demonstrates better noise performance, due to the reduction of device gate resistance. In addition, the MOS varactors designed with different gate layouts were used in a 5.2-GHz voltage-controlled oscillator (VCO) design, where the VCO with the stripe-shaped (2 /spl mu/m /spl times/ 36 fingers) gate varactor improved about 6 dB in phase-noise performance at 100-kHz offset frequency than that of square-shaped (8 /spl mu/m /spl times/ 9 fingers) gate varactor.     

Microwave power double-heterojunction HEMT's

The RF and dc characteristics of microwave power double-heterojunction HEMt's (DH-HEMT's) with low doping density have been studied. Small-signal RF measurements indicated that the cutoff frequency and the maximum frequency of oscillation in DH-HEMT's with 0.8-1 µm gate length and 1.2 mm gate periphery are typically 11- 16 GHz and 36-41 GHz, respectively. However, the cutoff frequency in DH-HEMT's degrades strongly with increasing drain bias voltage. This may be caused by both effects of increasing effective transit length of electrons and decreasing average electron velocity, due to Gunn domain formation. In large-signal microwave measurement, the DH-HEMT (2.4 mm gate periphery) delivered a maximum output power of 1.05 W with 2.8 dB gain and 0.58 W with 1.6 dB gain at 20 and 30 GHz, respectively. These are the highest output powers yet reported for HEMT devices. For the dc characteristics, the onset of two-terminal gate breakdown voltage is found to correlate with the drain current Idssand recessed length, and three-terminal source-drain breakdown characteristics near pinchoff are limited by the gate-drain breakdown. A simple model on gate breakdown voltage in HEMT is also presented.     

A new lossy substrate de-embedding method for sub-100 nm RF CMOS noise extraction and modeling

A new equivalent circuit method is proposed in this paper to de-embed the lossy substrate and lossy pads' parasitics from the measured RF noise of multifinger MOSFETs with aggressive gate length scaling down to 80 nm. A new RLC network model is subsequently developed to simulate the lossy substrate and lossy pad effect. Good agreement has been realized between the measurement and simulation in terms of S-parameters and four noise parameters, NF/sub min/ (minimum noise figure), R/sub n/ (noise resistance), Re(Y/sub sopt/), and Im(Y/sub sopt/) for the sub-100-nm RF nMOS devices. The intrinsic NF/sub min/ extracted by the new de-embedding method reveal that NF/sub min/ at 10 GHz can be suppressed to below 0.8 dB for the 80-nm nMOS attributed to the advancement of f/sub T/ to 100-GHz level and the effectively reduced gate resistance by multifinger structure.     

Photo-CVD SiO/sub 2/ layers on AlGaN and AlGaN-GaN MOSHFET

High-quality SiO/sub 2/ was successfully deposited onto AlGaN by photochemical vapor deposition (photo-CVD) using a D/sub 2/ lamp as the excitation source. The resulting interface state density was only 1.1 /spl times/ 10/sup 11/ cm/sup -2/eV/sup -1/, and the oxide leakage current was dominated by Poole-Frenkel emission. Compared with AlGaN-GaN metal-semiconductor HFET (MESHFETs) with similar structure, the gate leakage current is reduced by more than four orders of magnitude by using the photo-CVD oxide layer as gate oxide in AlGaN-GaN metal-oxide-semiconductor heterojunction field-effect transistors (MOSHFETs). With a 2-/spl mu/m gate, the saturated I/sub ds/, maximum g/sub m/ and gate voltage swing (GVS) of the fabricated nitride-based MOSHFET were 572 mA/mm, 68 mS/mm, and 8 V, respectively.     

Indium gallium arsenide microwave power transistors

Depletion-mode InGaAs microwave power MISFETs with 1-μm gate lengths and up to 1-mm gate widths have been fabricated using an ion-implanted process. The devices employed a plasma-deposited silicon/silicon dioxide gate insulator. The DC current-voltage (I -V) characteristics and RF power performance at 9.7 GHz are presented. The output power, power-added efficiency, and power gain as a function of input power are reported. An output power of 1.07 W at 9.7 GHz with a corresponding power gain and power-added efficiency of 4.3 dB and 38%, respectively, was obtained. The large-gate-width devices provided over twice the previously reported output power for InGaAs MISFETs at X-band. In addition, the first report of RF output stability of InGaAs MISFETs over 24 h period is also presented. An output power stability within 1.2% over 24 h of continuous operation was achieved. In addition, a drain current drift of 4% over 10⁴ s was obtained     

Experimental demonstration of a low-latency fiber soliton logicgate

We experimentally demonstrate switching in a 50 m-long soliton logic gate with a switching energy of 40 pJ using 490 fs pulses at 1.553 μm from an erbium-doped fiber laser. A full characterization of this gate shows a peak contrast ratio of 4.2:1, a timing window of 1.1 pulse width and cascadable operation. To our knowledge, the gate length of 50 m is at least six times shorter than other designs with comparable switching energies. The low-latency of this gate is possible due to a low-birefringent polarization-maintaining fiber that possesses a high polarization extinction ratio of up to 20 dB with a low birefringence of 2.6×10^-6. The low birefringence leads to a longer walk-off length between two orthogonally polarized pulses, where the walk-off length for 490 fs pulses is 56 m. We also study this gate numerically and find good agreement between the simulations and experiments     

GaAs LSI-directed MESFET's with self-aligned implantation for n+-layer technology (SAINT)

Self-aligned implantation for n⁺-layer technology (SAINT) has been developed for improvement in normally-off GaAs MESFET's to be used in LSI's. This technology has made it possible to arbitrarily control the spacing between the n⁺-implanted layer and gate contact by a dielectric lift-off process utilizing a multilayer resist with an undercut wall shape. SAINT FET's with a 1-µm gate length have above 200 mS/ mm transconductance in the normally-off region. The K value along the square-lawI - Vfitting has been improved by a factor of 3.4, compared to conventional FET's without the n⁺-layer. Thermal emission for carriers from the source n⁺-layer in the subthreshold region has been experimentally formulated. Threshold-voltage shift due to gate shortening for [011] gate FET's is definitely smaller than that for [011] gate FET's. The threshold-voltage standard deviations for [011] gate FET's with 2- and 1-µm gate lengths, obtained from a 6-mm × 9-mm area, are 9 and 34 mV, respectively. An E/D direct-coupled FET logics (DCFL) 15-stage ring oscillator with a 1-µm gate length shows a high switching speed of 45 ps/gate at a low supply voltage of 0.91 V.     

4H-SiC MESFET's with 42 GHz fmax

We report for the first time the development of state-of-the-art SiC MESFETs on high-resistivity 4H-SiC substrates. 0.5 μm gate MESFETs in this material show a new record high f_max of 42 GHz and RF gain of 5.1 dB at 20 GHz. These devices also show simultaneously high drain current, and gate-drain breakdown voltage of 500 mA/mm, and 100 V, respectively showing their potential for RF power applications     

DC and RF characteristics of E-mode Ga/sub 0.51/In/sub 0.49/P-In/sub 0.15/Ga/sub 0.85/As pseudomorphic HEMTs

The DC and RF characteristics of Ga/sub 0.49/In/sub 0.51/P-In/sub 0.15/Ga/sub 0.85/As enhancement- mode pseudomorphic HEMTs (pHEMTs) are reported for the first time. The transistor has a gate length of 0.8 /spl mu/m and a gate width of 200 /spl mu/m. It is found that the device can be operated with gate voltage up to 1.6 V, which corresponds to a high drain-source current (I/sub DS/) of 340 mA/mm when the drain-source voltage (V/sub DS/) is 4.0 V. The measured maximum transconductance, current gain cut-off frequency, and maximum oscillation frequency are 255.2 mS/mm, 20.6 GHz, and 40 GHz, respectively. When this device is operated at 1.9 GHz under class-AB bias condition, a 14.7-dBm (148.6 mW/mm) saturated power with a power-added efficiency of 50% is achieved when the drain voltage is 3.5 V. The measured F/sub min/ is 0.74 dB under I/sub DS/=15 mA and V/sub DS/=2 V.     

90-nm CMOS for microwave power applications

We report, for the first time, the experimental evaluation of a very short channel 90-nm CMOS transistor under RF over-voltage conditions. At 9 GHz and 1.5 V supply a 40 /spl mu/m gate width device is able to deliver 370 mW/mm output power with a PAE of 42% and a transducer power gain of 15 dB. Measurement results at 3 and 6 GHz is also presented. The transistor does not show any degradation in either dc or RF performance after prolonged operation at 1 and 6 dB compression. Simulation show, that the peak voltage, V/sub ds/ at this condition is 3.0 V, while the maximum allowed dc supply voltage is limited by the design rules to 1.2 V. We show for the first time that nanometer-scale CMOS can be used for microwave power applications with severe RF over-voltage conditions without any observable degradation.     

InGaAs field-effect transistors with submicron gates forK-band applications

Depletion mode InGaAs microwave power MISFETs with 0.7 μm gate lengths and 0.2 mm gate widths have been fabricated using an epitaxial process. The devices employed a plasma deposited silicon dioxide gate insulator. The RF power performance at 18 GHz, 20 GHz, and 23 GHz is presented. An output power density of 1.04 W/mm with a corresponding power gain and power-added efficiency of 3.7 dB and 40%, respectively, was obtained at 18 GHz. This is the highest output power density obtained for an InGaAs based transistor on InP at K-band. Record output power densities for an InGaAs MISFET were also demonstrated to the stable within 3% over 17 hours of continuous operation at 18 GHz     

A wide-band T/R switch using enhanced compact Waffle MOSFETs

A wide-band complementary metal oxide semiconductor (CMOS)transmit/receive (T/R) switch using enhanced compact waffle metal-oxide-semiconductor field-effect transistors (MOSFETs) is presented. The compact waffle layout configuration saves much active area to give a low on-resistance. Furthermore,the low drain-to-substrate capacitance (CDB) in waffle MOSFETs can help reduce high frequency substrate coupling and substrate loss for CMOS radio frequency (RF)/microwave integrated circuits (ICs). A 2-dB higher maximum stable gain/maximum available gain (MSG/MAG)and a 2-GHz higher f/sub max/ are obtained compared with those of conventional multifinger MOSFETs. The CMOST/R switch implemented in a standard 0.35-/spl mu/m CMOS technology gives a low insertion loss of 1.7dB,high isolation of more than 40dB, larger than 15-dB return loss, 7-dBm P/sub 1 dB/ and 13-dBm input IP3 at 900MHz with a 3-V supply voltage. The switch maintains a wide-band performance up to 2.4GHz with only a slight deterioration.     

Unpassivated AlGaN-GaN HEMTs with minimal RF dispersion grown by plasma-assisted MBE on semi-insulating 6H-SiC substrates

High electron mobility transistors (HEMTs) are fabricated from AlGaN-GaN heterostructures grown by plasma-assisted molecular beam epitaxy (MBE) on semi-insulating 6H-SiC substrates. At a sheet charge density of 1.3 /spl times/ 10/sup 13/ cm/sup -2/, we have repeatedly obtained electron mobilities in excess of 1350 cm/sup 2//Vs. HEMT devices with a gate length of 1/spl mu/m, a gate width of 200 /spl mu/m, and a source-drain spacing of 5 /spl mu/m show a maximum drain current of 1.1 A/mm and a peak transconductance of 125 mS/mm. For unpassivated HEMTs, we measured a saturated power output of 8.2-W/mm continuous wave (cw) at 2 GHz with an associated gain of 11.2 dB and a power-added efficiency of 41%. The achievement of high-power operation without a surface passivation layer suggests that free surface may not be the dominant source of radio-frequency (RF) dispersion in these MBE-grown structures. This data may help discriminate between possible physical mechanisms of RF dispersion in AlGaN-GaN HEMTs grown by different techniques.