J. Kruse

Microwave surface impedance at 10 GHz and quasiparticle scattering in YBa2Cu3O7 films

The surface impedance of superconducting YBa2Cu3O7 films as a function of temperature at 10 GHz has been measured in a parallel plate resonator geometry. The penetration depth λ(T), complex microwave conductivity σ(T), and quasiparticle scattering rate 1/τ(T) were also determined. After a rapid fall as T is lowered below Tc, the surface resistance Rs exhibits a linear dependence from 65 K down to 6 K. As T drops below Tc, the real part of the conductivity σ1 has a rapid rise, which is attributed to the observed dramatic increase in τ. The normal‐fluid density shows a linear behavior at low temperatures, which is inconsistent with s‐wave BCS superconductivity.

Temperature dependent study of the microwave performance of 0.25-/spl mu/m gate GaAs MESFETs and GaAs pseudomorphic HEMTs

We report on the noise figure, associated gain, and the current gain cutoff frequency for comparable 0.25-/spl mu/m gate GaAs MESFETs and GaAs pseudomorphic HEMTs (p-HEMTs) as a function of cryogenic temperature. Contrary to previously published results which suggest that p-HEMTs should have a higher electron velocity and a lower noise figure than MESFETs due to the effects of the two-dimension electron gas (2-DEG), we have experimentally verified that this is not the case. We show clear evidence that the transport properties of the 2-DEG in p-HEMTs do not make a significant contribution to the speed enhancement and noise reduction during high-frequency operation of these devices. It is the fundamental InGaAs material properties, specifically the /spl Gamma/-L valley separation in the conduction band and associated effective mass of the electron in either GaAs or InGaAs channel, which limits the high-field electron velocity and thus the speed and noise performance of the devices.

Temperature dependent study of carbon-doped InP/InGaAs HBT's

We report on a temperature dependent study of the dc and the microwave performance of carbon-doped InP/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistors (HBTs). The turn on voltage increased 114% and the dc current gain decreased 25% as the temperature was reduced from 300 K to 33 K. Under high-current injection, there was a 29% increase in the current gain cutoff frequency of these devices as the temperature was lowered from 300 K to 77 K. By investigating the operation of HBTs at cryogenic temperatures, increased understanding of the mechanisms of carrier transport in these devices can be obtained, and this may lead to improvements in device performance.

Cryogenic small-signal model for 0.55 mu m gate-length ion-implanted GaAs MESFET's

The cryogenic microwave performance of 0.5*300- mu m gate ion-implanted GaAs MESFETs is presented. The devices studied have been fabricated as part of a process control monitor chip (PCM) which uses comparable industry standard design rules. Detailed small-signal element modeling has been performed to determine the temperature dependence of important physical parameters over a lattice temperature range from 300 K to 115 K. The authors find appreciable improvement in cut-off frequency (f/sub T/) and well behaved temperature dependence of transconductance (g/sub m/) and gate-source capacitance (C/sub gs/). Empirical relations for the temperature dependence of f/sub T/, the maximum frequency of oscillation (f/sub max/), g/sub m/ and C/sub gs/, that should provide accurate temperature-dependent device and circuit models are presented.<<ETX>>

Temperature dependence study of two-dimensional electron gas effect on the noise performance of high frequency field effect transistors

We present experimental evidence that the noise figure (NF) and associated gain equal to those achieved with GaAs pseudomorphic high electron mobility transistors (GaAs p-HEMTs) can also be accomplished by ion implanted GaAs metal-semiconductor field-effect transistors (GaAs MESFETs). These measured noise figure results as a function of low temperature for GaAs MESFETs and p-HEMTs clearly suggest that the transport properties of the two-dimensional electron gas in HEMTs and p-HEMTs do not make a significant contribution to the noise reduction at high frequency operation of these devices.<<ETX>>

Low-power performance of 0.5- mu m JFET for low-cost MMIC's in personal communications

The low-power microwave performance of an enhancement-mode ion-implanted GaAs JFET is reported. A 0.5- mu m*100- mu m E-JFET with a threshold voltage of V/sub th/=0.3 V achieved a maximum DC transconductance of g/sub m/=489 mS/mm at V/sub ds/=1.5 V and I/sub ds/=18 mA. Operating at 0.5 mW of power with V/sub ds/=0.5 V and I/sub ds/=1 mA, the best device on a 3-in wafer achieved a noise figure of 0.8 dB with an associated gain of 9.6 dB measured at 4 GHz. Across a 3-in wafer the average noise figure was F/sub min/=1.2 dB and the average associated gain was G/sub a/=9.8 dB for 15 devices measured. These results demonstrate that the E-JFET is an excellent choice for low-power personal communication applications.<<ETX>>

Ultra low-noise performance of 0.15-micron gate GaAs MESFET's made by direct ion implantation for low-cost MMIC's applications

The high-speed and noise performance of 0.15- mu m gate GaAs MESFETs for microwave and millimeter-wave IC applications is reported. The best extrinsic f/sub t/ is 109 GHz without correction for pad parasitics, which is equivalent to an intrinsic f/sub t/ of 134 GHz. The 0.15- mu m*200- mu gate GaAs MESFET achieved a 0.6-dB noise figure with a 17-dB associated gain at 10 GHz and a 0.9-dB noise figure with a 13-dB associated gain at 18 GHz. The measured noise figure and associated gain are the best reported for GaAs MESFETs and are comparable to the best noise/gain performance of HEMTs and P-HEMTs.<<ETX>>

High temperature superconducting resonators and switches: design, fabrication, and characterization

We report our recent efforts in designs of several RF and microwave devices using high temperature superconducting (HTS) thin film technology. Devices considered include transmission lines, resonators, switches, and phase shifters in microstrip, stripline and coplanar waveguide. The circuit design, modeling, simulation, fabrication, packaging, and testing are discussed. Using a two-dimensional (2-D) EM simulator, we have optimized the geometry of the RF microstrip and stripline resonators for frequencies near 900 MHz. An unloaded Q is obtained as high as 80,000, three orders of magnitude greater than the traditional 2-D gold or copper resonators with identical structures. On-wafer probe and bit-error rate measurements show that the HTS transmission lines have an extremely small insertion loss and dispersion; thus they are ideal candidates for applications in multichip module interconnects and delay lines. A sharp switching characteristic and an unusually strong RF power hysteresis loop have been observed in the HTS lines. This interesting behavior has been utilized for designs of new HTS microwave phase shifters. The use of HTS lines can substantially reduce the losses suffered by conventional PIN diode switches.

Eye‐diagram and scattering parameter characterization of superconducting and gold coplanar transmission lines

We report the gigahertz experimental results of time and frequency performance on YBCO high‐temperature superconductor and gold coplanar transmission lines. An on‐wafer direct probing measurement system was used to collect data at cryogenic temperatures on both YBCO and gold coplanar lines. The insertion loss of the 6 cm lines at a frequency of 2.5 GHz was measured to be −0.03 dB for the superconducting line compared to −10.4 dB for the gold line at 80 K. Eye‐diagram measurements were performed on the packaged lines and show the correlation between the insertion loss of the line and the attenuation of a pseudorandom bit sequence. The measured eye height was 170 mV for the YBCO compared to 90 mV for a gold line at 1 Gbit/s and a temperature of 77 K for the packaged 6 cm lines.

Microwave performance of low-power ion-implanted 0.25-micron gate GaAs MESFET for low-cost MMIC's applications

Low-power microwave performance of an enhancement mode) (E-mode ion-implanted GaAs MESFET is reported. The 0.25- mu m*100- mu m E-MESFET has a threshold voltage of V/sub th/=0.0 V. At 1.0-mW operation of power with a bias condition of V/sub ds/=0.5 V and I/sub ds/-2 mA, a noise figure of 0.85 dB with an associated gain of 15 dB was measured at 4 GHz. These results demonstrate that the GaAs E-MESFET is an excellent choice for low-power personal communication applications.<<ETX>>