Long-wavelength In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As large-area avalanche photodiodes and arrays

Large-area (500-/spl mu/m diameter) mesa-structure In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiodes (APDs) are reported. The dark current density was /spl sim/2.5/spl times/10/sup -2/ nA//spl mu/m/sup 2/ at 90% of breakdown; low surface leakage current density (/spl sim/4.2 pA//spl mu/m) was achieved with wet chemical etching and SiO/sub 2/ passivation. An 18 /spl times/ 18 APD array with uniform distributions of breakdown voltage, dark current, and multiplication gain has also been demonstrated. The APDs in the array achieved 3-dB bandwidth of /spl sim/8 GHz at low gain and a gain-bandwidth product of /spl sim/120 GHz.     

Integrated high-/spl kappa/ (/spl kappa/ /spl sim/19) MIM capacitor with Cu/low-/spl kappa/ interconnects for RF application

We demonstrate a high-performance metal-high /spl kappa/ insulator-metal (MIM) capacitor integrated with a Cu/low-/spl kappa/ backend interconnection. The high-/spl kappa/ used was laminated HfO/sub 2/-Al/sub 2/O/sub 3/ with effective /spl kappa/ /spl sim/19 and the low-/spl kappa/ dielectric used was Black Diamond with /spl kappa/ /spl sim/2.9. The MIM capacitor (/spl sim/13.4 fF//spl mu/m/sup 2/) achieved a Q-factor /spl sim/53 at 2.5 GHz and 11.7 pF. The resonant frequency f/sub r/ was 21% higher in comparison to an equivalently integrated Si/sub 3/N/sub 4/-MIM capacitor (/spl sim/0.93 fF//spl mu/m/sup 2/) having similar capacitance 11.2 pF. The impacts of high-/spl kappa/ insulator and low-/spl kappa/ interconnect dielectric on the mechanism for resonant frequency improvement are distinguished using equivalent circuit analysis. This letter suggests that integrated high-/spl kappa/ MIM could be a promising alternative capacitor structure for future high-performance RF applications.     

A 310/spl deg//3.6-dB K-band phaseshifter using paraelectric BST thin films

Ferro- and para-electric BaSrTiO/sub 3/ (/spl epsiv//sub r//spl sim/350 and tg/spl delta//spl sim/5/spl times/10/sup -2/ at 0V) thin films were deposited by low-cost sol-gel techniques. Subsequently, the films were used for fabricating coplanar waveguide phaseshifters using tunable finger-shaped capacitors. A 310/spl deg/ phaseshift was obtained at 30GHz and 35V of tuning voltage with 3.6dB of insertion loss yielding a figure of merit of 85/spl deg//dB.     

SOI technology for radio-frequency integrated-circuit applications

This paper presents a silicon-on-insulator (SOI) integration technology, including structures and processes of OFF-gate power nMOSFETs, conventional lightly doped drain (LDD) nMOSFETs, and spiral inductors for radio frequency integrated circuit (RFIC) applications. In order to improve the performance of these integrated devices, body contact under the source (to suppress floating-body effects) and salicide (to reduce series resistance) techniques were developed for transistors; additionally, locally thickened oxide (to suppress substrate coupling) and ultra-thick aluminum up to 6 /spl mu/m (to reduce spiral resistance) were also implemented for spiral inductors on high-resistivity SOI substrate. All these approaches are fully compatible with the conventional CMOS processes, demonstrating devices with excellent performance in this paper: 0.25-/spl mu/m gate-length offset-gate power nMOSFET with breakdown voltage (BV/sub DS/) /spl sim/ 22.0 V, cutoff frequency (f/sub T/)/spl sim/15.2 GHz, and maximal oscillation frequency (f/sub max/)/spl sim/8.7 GHz; 0.25-/spl mu/m gate-length LDD nMOSFET with saturation current (I/sub DS/)/spl sim/390 /spl mu/A//spl mu/m, saturation transconductance (g/sub m/)/spl sim/197 /spl mu/S//spl mu/m, cutoff frequency /spl sim/ 25.6 GHz, and maximal oscillation frequency /spl sim/ 31.4 GHz; 2/5/9/10-nH inductors with maximal quality factors (Q/sub max/) 16.3/13.1/8.95/8.59 and self-resonance frequencies (f/sub sr/) 17.2/17.7/6.5/5.8 GHz, respectively. These devices are potentially feasible for RFIC applications.     

A 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdown voltage, respectively. External quantum efficiency was above 40% in the wavelength range from 1.0 to 1.6 /spl mu/m. It was /spl sim/57% and /spl sim/45% at 1.3 and 1.55 /spl mu/m, respectively. A bandwidth of 13 GHz was achieved at low gain.     

An experimental study of harmonic SIS mixing at 205-235 GHz

A 230-GHz subharmonically pumped waveguide mixer employing superconducting tunnel junctions has been developed. We present, in this paper, an experimental study of harmonic superconductor-insulator-superconductor (SIS) mixing at 230 GHz, focusing mainly on its noise behavior. The mixer has a double-tuned waveguide structure and employs an array of four 1.7-/spl mu/m/sup 2/ Nb-AlOx-Nb SIS junctions in series, with /spl omega/R/sub n/C/sub j//spl sim/3 at 230 GHz. Harmonic quantum mixing occurred over an experimental frequency range of 205-235 GHz (local oscillator: 112.5-117.5 GHz), exhibiting corresponding double sideband noise temperatures of lower than 150 K, with a lowest value of 75 K at /spl sim/230 GHz. The measured mixer noise is believed to be the lowest yet reported for a mixer using subharmonic-pump configuration at this frequency. A phenomenon that we attribute to the third harmonic SIS mixing has also been observed.     

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.     

Device scaling physics and channel velocities in AIGaN/GaN HFETs: velocities and effective gate length

This paper addresses scaling issues in AIGaN/GaN heterojunction field-effect transistors (HFETs) using ensemble Monte Carlo techniques. For gate lengths below 0.25 /spl mu/m, f/sub T/ values are known not to scale linearly with the inverse gate length. The authors' simulations show this to be due to an increasing difference between the lithographic gate length and the effective gate length as the devices shrink. The results for AIGaN/GaN are compared with In/sub 0.52/Al/sub 0.48/-In/sub 0.53/Ga/sub 0.47/As-InP devices, and the authors found that the limiting role of velocity overshoot and depletion region spread causes the GaN HFETs to have a peak f/sub T/ of /spl sim/ 220 GHz compared to /spl sim/ 500 GHz for InGaAs devices.     

Distributed phase shifter with pyrochlore bismuth zinc niobate thin films

A monolithic Ku-band phase shifter employing voltage tunable Bi/sub 1.5/Zn/sub 1.0/Nb/sub 1.5/O/sub 7/ (BZN) thin film parallel plate capacitors is reported. BZN films were deposited by radio frequency magnetron sputtering on single-crystal sapphire substrates. A nine-section distributed coplanar waveguide loaded-line phase-shifter structure was designed. A differential phase shift of 175/spl deg/ was achieved with a maximum insertion loss of 3.5 dB at 15 GHz, giving a figure of merit /spl sim/50/spl deg//dB. To the best of our knowledge, this is the first demonstration of a monolithic tunable microwave circuit using BZN thin films.     

Low-voltage high performance compact all cascode CMOS current mirror

A high performance and compact current mirror with extremely low input and high output resistances (R/sub in//spl sim/0.01/spl Omega/, R/sub out//spl sim/10 G/spl Omega/), high copying accuracy, very low input and output voltage requirements (V/sub in/, V/sub out//spl ges/V/sub DSsat/), high bandwidth (200 MHz using a 0.5 /spl mu/m CMOS technology) and low settling time (25 ns) is proposed. Simulations and experimental results are shown that validate the circuit.     

Diamond FET using high-quality polycrystalline diamond with f/sub T/ of 45 GHz and f/sub max/ of 120 GHz

Using high-quality polycrystalline chemical-vapor-deposited diamond films with large grains (/spl sim/100 /spl mu/m), field effect transistors (FETs) with gate lengths of 0.1 /spl mu/m were fabricated. From the RF characteristics, the maximum transition frequency f/sub T/ and the maximum frequency of oscillation f/sub max/ were /spl sim/ 45 and /spl sim/ 120 GHz, respectively. The f/sub T/ and f/sub max/ values are much higher than the highest values for single-crystalline diamond FETs. The dc characteristics of the FET showed a drain-current density I/sub DS/ of 550 mA/mm at gate-source voltage V/sub GS/ of -3.5 V and a maximum transconductance g/sub m/ of 143 mS/mm at drain voltage V/sub DS/ of -8 V. These results indicate that the high-quality polycrystalline diamond film, whose maximum size is 4 in at present, is a most promising substrate for diamond electronic devices.     

Microwave performance of GaAs MOSFET with wet thermally oxidized InAlP gate dielectric

This paper reports the first demonstration of a microwave-frequency operation of a GaAs MOSFET fabricated using a wet thermal oxidization of InAlP lattice-matched to GaAs to form a native-oxide gate insulator. Devices with 1-/spl mu/m gate lengths exhibit a cutoff frequency (f/sub t/) of 13.7 GHz and a maximum frequency of oscillation (f/sub max/) of 37.6 GHz, as well as a peak extrinsic transconductance of 73.6 mS/mm. A low-leakage current density of 3.8/spl times/10/sup -3/ A/cm/sup 2/ at 1-V bias for an MOS capacitor demonstrates the good insulating properties of the /spl sim/ 11-nm thick native gate oxide.     

Graded base type-II InP/GaAsSb DHBT with f/sub T/=475 GHz

The first demonstration of a type-II InP/GaAsSb double heterojunction bipolar transistor (DHBT) with a compositionally graded InGaAsSb to GaAsSb base layer is presented. A device with a 0.4/spl times/6 /spl mu/m/sup 2/ emitter dimensions achieves peak f/sub T/ of 475 GHz (f/sub MAX/=265 GHz) with current density at peak f/sub T/ exceeding 12 mA//spl mu/m/sup 2/. The structure consists of a 25-nm InGaAsSb/GaAsSb graded base layer and 65-nm InP collector grown by MBE with breakdown voltage /spl sim/4 V which demonstrates the vertical scaling versus breakdown advantage over type-I DHBTs.     

Power scaling of a flashlamp-pumped Cr:LiSAF thin-slab zig-zag laser

We report on the power scaling of a flashlamp-pumped Cr:LiSrAlF/sub 6/ thin-slab zig-zag laser operating at repetition rates up to 5 Hz. Average output power of 44 W with pulse energies of 8.8 J was achieved operating with a stable cavity. Excellent medium control was also obtained during this operation. Also demonstrated at 5 Hz was operation at energies /spl sim/ 0.5 J in Q-switched mode with unstable optics and bandwidth control, beam quality < 1.5 XDL, bandwidth /spl sim/ 1 GHz, and root-mean-square beam jitter of less than half of a diffraction limited far-field spot radius.     

A submicrometer 252 GHz f/sub T/ and 283 GHz f/sub MAX/ InP DHBT with reduced C/sub BC/ using selectively implanted buried subcollector (SIBS)

The selectively implanted buried subcollector (SIBS) is a method to decouple the intrinsic and extrinsic C/sub BC/ of InP-based double-heterojunction bipolar transistors (DHBTs). Similar to the selectively implanted collector (SIC) used in Si-based bipolar junction transistors (BJTs) and HBTs, ion implantation is used to create a N+ region in the collector directly under the emitter. By moving the subcollector boundary closer to the BC junction, SIBS allows the intrinsic collector to be thin, reducing /spl tau//sub C/, while simultaneously allowing the extrinsic collector to be thick, reducing C/sub BC/. For a 0.35 /spl times/ 6 /spl mu/m/sup 2/ emitter InP-based DHBT with a SIBS, 6 fF total C/sub BC/ and >6 V BV/sub CBO/ were obtained with a 110-nm intrinsic collector thickness. A maximum f/sub T/ of 252 GHz and f/sub MAX/ of 283 GHz were obtained at a V/sub CE/ of 1.6 V and I/sub C/ of 7.52 mA. Despite ion implantation and materials regrowth during device fabrication, a base and collector current ideality factor of /spl sim/2.0 and /spl sim/1.4, respectively, at an I/sub C/ of 100 /spl mu/A, and a peak dc /spl beta/ of 36 were measured.     

High-performance InGaP/GaAs HBTs with compositionally graded bases grown by solid-source MBE

N-p-n InGaP/GaAs heterojunction bipolar transistors (HBTs) with compositionally graded In/sub x/Ga/sub 1-x/As (Be doped) bases have been successfully grown by solid-source molecular beam Epitaxy (SSMBE) using a gallium phosphide (GaP) decomposition source. In this paper, the dc and RF characteristics of HBTs with different indium mole fractions in the graded In/sub x/Ga/sub 1-x/As base (x:0 /spl rarr/ ;0.1 and x:0 /spl rarr/ 0.05) are measured to investigate optimum-grading profiles. The measured average current gains, /spl beta/s of a control sample, a 10% graded-base sample and a 5% graded-base sample, are 162, 397 and 362, respectively. To our knowledge, these current gains are the highest values ever reported in compositionally graded-base InGaP/GaAs HBTs with a base sheet resistance R/sub sh/ of /spl sim/200 /spl Omega//sq establishing a new benchmark for InGaP/GaAs HBTs. Furthermore, these compositionally graded-base HBTs show higher unity current/gain cutoff frequency, f/sub T/ and maximum oscillation frequency, f/sub max/. Compared to the control sample with the same base thickness, the base transit time /spl tau//sub B/ of the graded sample is reduced by /spl sim/15% to /spl sim/20% by the induced built-in potential, resulting in an increase of f/sub max/ from 16 to 18.5 GHz in a device with an emitter size of 10/spl times/10 /spl mu/m/sup 2/. Additionally, for the 5% graded-base sample, with a 5/spl times/5 /spl mu/m/sup 2/ emitter region, f/sub T/ and f/sub max/ are 16.3 and 33.8 GHz, respectively, under low-level collector current. These results demonstrate that InGaP/GaAs HBTs with In/sub x/Ga/sub 1-x/As graded-base layers (x:0 /spl rarr/ 0.05) have the potential for high-speed analogue to digital converters.     

BCB-bridged distributed wideband SPST switch using 0.25-/spl mu/m In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As metamorphic HEMTs

In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As metamorphic high-electron mobility transistor (mHEMT) dc-30 GHz distributed single-pole-single through (SPST) switches were designed and fabricated using the low-/spl kappa/ benzocyclobutene (BCB) bridged technology. The current gain cutoff frequency, and the electron transit time of In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As mHEMTs have been investigated. By analyzing the extrinsic total delay time, the effective velocity of electrons can be estimated, and the average velocity is 2.3/spl times/10/sup 7/cm/s. The dc-30 GHz distributed wideband SPST switch exhibits an insertion loss of less than 5.5 dB, and an isolation larger than 30 dB, which is the first demonstration of the high-isolation of InAlAs-InGaAs mHEMTs monolithic switch. As to the power performance, this switch can handle the power up to 12 dBm at 2.4 GHz. After over 250 h of 85-85 (temperature =85/spl deg/C, humidity =85%) environmental evaluation, this BCB passivated and bridged microwave and monolithic integrated circuit switch demonstrates reliable RF characteristics without any significant performance change, which proves that this process using the low-/spl kappa/ BCB layer is attractive for millimeter-wave circuit applications.     

A Ka-band power amplifier based on the traveling-wave power-dividing/combining slotted-waveguide circuit

An eight-device Ka-band solid-state power amplifier has been designed and fabricated using a traveling-wave power-dividing/combining technique. The low-profile slotted-waveguide structure employed in this design provides not only a high power-combining efficiency over a wide bandwidth, but also efficient heat sinking for the active devices. The measured maximum small-signal gain of the eight-device power amplifier is 19.4 dB at 34 GHz with a 3-dB bandwidth of 3.2 GHz (f/sub L/=31.8 GHz, f/sub H/=35 GHz). The measured maximum output power at 1-dB compression (P/sub out/ at 1 dB) from the power amplifier is 33 dBm (/spl sim/2 W) at 32.2 GHz, with a power-combining efficiency of 80%. Furthermore, performance degradation of this power amplifier due to device failures has also been simulated and measured.     

AlGaN/GaN/InGaN/GaN DH-HEMTs with an InGaN notch for enhanced carrier confinement

We report an AlGaN/GaN/InGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) with high-mobility two-dimensional electron gas (2-DEG) and reduced buffer leakage. The device features a 3-nm thin In/sub x/Ga/sub 1-x/N(x=0.1) layer inserted into the conventional AlGaN/GaN HEMT structure. Assisted by the InGaN layers polarization field that is opposite to that in the AlGaN layer, an additional potential barrier is introduced between the 2-DEG channel and buffer, leading to enhanced carrier confinement and improved buffer isolation. For a sample grown on sapphire substrate with MOCVD-grown GaN buffer, a 2-DEG mobility of around 1300 cm/sup 2//V/spl middot/s and a sheet resistance of 420 /spl Omega//sq were obtained on this new DH-HEMT structure at room temperature. A peak transconductance of 230 mS/mm, a peak current gain cutoff frequency (f/sub T/) of 14.5 GHz, and a peak power gain cutoff frequency (f/sub max/) of 45.4 GHz were achieved on a 1/spl times/100 /spl mu/m device. The off-state source-drain leakage current is as low as /spl sim/5 /spl mu/ A/mm at V/sub DS/=10 V. For the devices on sapphire substrate, maximum power density of 3.4 W/mm and PAE of 41% were obtained at 2 GHz.     

Continuous-fiber modulator with high-bandwidth coplanar strip electrodes

Operation of a continuous-fiber modulator based on coupling from a fiber side-polished beyond cut-off to a multimode planar waveguide has been demonstrated for the first time at gigahertz frequencies. The bandwidth of the modulator electrode structure was /spl sim/4 GHz while the optical insertion loss was measured at <0.5 dB. The device was used to produce mode-locked pulse trains in an erbium fiber laser at repetition rates of /spl sim/3 GHz.