Chen-Yu Chi

Planar microwave and millimeter-wave lumped elements and coupled-line filters using micro-machining techniques

Planar microwave and millimeter-wave inductors and capacitors have been fabricated on high-resistivity silicon substrates using micro-machining techniques. The inductors and capacitors are suspended on a thin dielectric membrane to reduce the parasitic capacitance to ground. The resonant frequencies of a 1.2 nH and a 1.7-nH inductor have been increased from 22 GHz and 17 GHz to around 70 GHz and 50 GHz, respectively. We also report on the design and measurement of a new class of stripline filters suspended on a thin dielectric membrane. Interdigitated filters with 43% and 5% bandwidth have been fabricated and exhibit a port-to-port 0.7 dB and 2.0 dB loss, respectively, at 14-15 GHz. The micro-machining fabrication technique can be used with silicon and GaAs substrates in microstrip or coplanar-waveguide configurations to result in planar low-loss lumped elements and filters suitable for monolithic integration or surface mount devices up to 100 GHz. >

Design of Lange-couplers and single-sideband mixers using micromachining techniques

This paper reports on the design and performance of micromachined Lange-couplers and single-sideband mixers (SSB) on thin dielectric membranes at Ku-band. The micromachined Lange-coupler results in a 3.6/spl plusmn/0.8 dB coupling bandwidth from 6.5 to 20 GHz. The Lange-coupler and an interdigital filter are used in a 17-GHz SSB. The SSB mixer requires 1-2 mW of local oscillator (LO) power without dc bias and achieves a 30 dB upper-sideband (USB) image rejection for an IF frequency of 1 GHz and above. The micromachined membrane technology can be easily scaled to millimeter-wave monolithic microwave integrated circuits (MMICs) to meet the low-cost requirements in automotive or portable communication systems.

Conductor-loss limited stripline resonator and filters

We report on stripline resonators on thin dielectric membranes that show dispersion-free, conductor-loss limited performance at 13.5 GHz, 27.3 GHz, and 39.6 GHz. The unloaded-Q (Q/sub u/) of the resonators increases as /spl radic/f with frequency and is measured to be 386 at 27 GHz. The measured results agree well with a new conformal mapping analysis. The stripline resonators are used in a micromachined state-of-the-art planar interdigitated bandpass filter at K-band frequencies. Excellent agreement has been achieved between the microwave model at 850 MHz and the 20 GHz filter. The micromachined filter exhibits a passband return loss better than -15 dB and a conductor-loss limited 1.7 dB port-to-port insertion loss (including input/output CPW line loss) at 20.3 GHz.

A 40 GHz integrated quasi optical slot HFET mixer

We present for the first time a quasi optical mixer realized as a resistive HFET mixer with an integrated slot antenna. The mixer circuit conversion loss, defined as the measured IF-power in the 50 ohm load divided by the RF-power available at the slot-antenna terminals, is approximately 7 dB at an LO-power of 10.5 dBm when the mixer is fundamentally pumped, and 16 dB for subharmonically pumping at 10 dBm LO-power.<<ETX>>

A low-loss 20 GHz micromachined bandpass filter

We report on the results of a state-of-the-art planar interdigitated bandpass filter at K-band by using micromachining techniques. In this design, a microwave model was first built at 850 MHz to simulate the K-band filter, and the 20 GHz micromachined filter was fabricated based on the 850 MHz microwave model. Excellent agreement has been achieved between the microwave model and the 20 GHz filter. The micromachined filter exhibits a return loss better than -15 dB within the passband and a 1.7 dB port-to-port insertion loss at 20.3 GHz. A grounded coplanar waveguide with a micromachined mouse-hole shielding structure has also been carefully examined. The grounded coplanar waveguide structure is used in the micromachined filter as the input/output feeding line and exhibits a return loss better than -20 dB up to 32 GHz.<<ETX>>

Planar millimeter-wave microstrip lumped elements using micro-machining techniques

Planar millimeter-wave microstrip inductors and capacitors have been fabricated on high-resistivity silicon substrates using micro-machining techniques. The spiral inductors and interdigitated capacitors are suspended on a thin dielectric membrane to reduce the parasitic capacitance to ground. The resonant frequencies of a 1.2 nH and a 1.7 nH inductor fabricated on a high-resistivity silicon substrate and on a small dielectric membrane, have been increased from 22 GHz and 17 GHz to 73 GHz and 54 GHz, respectively. The planar micro-machined elements are compatible with the via-hole technology process in GaAs and InP MMIC, and can be used as true inductors and capacitors up to 50-60 GHz. The technique can be also applied to lumped elements in coplanar-waveguide transmission lines.<<ETX>>

A 40-GHz integrated quasi-optical slot HFET mixer

We present for the first time a quasi-optical mixer realized as a resistive HFET mixer with an integrated slot antenna. Two different types of HFETs, based on GaAs and InP, are compared for this application. The mixer conversion loss, defined as the measured IF power in the 50 /spl Omega/ load divided by the RF power available at the slot-antenna terminals, is better than 7 dB at LO powers down to 0 dBm. Subharmonic pumping of the mixer is also investigated. This topology has a potential interest for future low-cost millimeter-wave receivers for automobile radar and speed detector systems. >

The fabrication and performance of planar doped barrier diodes as 200 GHz subharmonically pumped mixers

The PDB (planar doped barrier) diode consists of a p/sup +/ doping spike between two intrinsic layers and n/sup +/ ohmic contacts. Such devices can have an anti-symmetric current vs. voltage characteristic. The capacitance is approximately constant with the applied voltage, and the barrier height and device capacitance are easily adjustable. These characteristics make the PDB a candidate for millimeter- and submillimeter-wave subharmonic mixers. We have fabricated 2 and 4 /spl mu/m diameter diodes with different barrier designs using GaAs epi-layers. The devices are planarized using an air-bridge and a surface channel etch. After completely removing the substrate, the devices are mounted on a quartz substrate to reduce parasitic effects. Diced diodes were tested as subharmonic mixers around 200 GHz in both a quasi-optical planar wideband subharmonic receiver and a planar-diode waveguide-mixer. The quasi-optical measurements show that a 0.23 V (and 0.4 V) barrier height GaAs diode with 2.0 /spl mu/A (and 5 nA) of saturation current gives a DSB conversion loss of 10.8 dB (and 9.5 dB) and a DSB noise temperature of 3795/spl deg/ K and 2450/spl deg/ K). The waveguide mixer measurements were made with a similar 0.23 V barrier height PDB. Such a mixer has a minimum conversion loss of 10.2 dB and noise temperature of 3570/spl deg/ K, and requires only 1.2 milliwatts of available LO power. >

A novel biased anti-parallel Schottky diode structure for subharmonic mixing

Subharmonically pumped mixers using zero-biased anti-parallel Schottky diode pairs produce good results, but require a larger LO power than biased Schottky diodes. Presented here is a novel planar-diode anti-parallel pair that allows independent biasing of the two diodes. This diode pair is integrated into a quasi-optical wideband receiver and the RF measurements on a 1.2-/spl mu/m anode diameter pair show a reduced LO power requirement at 180 GHz by a factor of 2 to 3 with a similar DSB conversion loss and noise temperature (9.7 dB and 1850 K) to an unbiased Schottky diode pair. This structure has potential for applications at submillimeter-wave frequencies where a large amount of LO power is not easily available.<<ETX>>

A quasi-optical subharmonically-pumped receiver using separately biased Schottky diode pairs

A novel quasi-optical planar subharmonically pumped receiver including a log-periodic antenna and an anti-parallel Schottky diode pair with independent bias is presented. The antenna and Schottky diode pair have a 20 /spl mu/m and 2.5 /spl mu/m wide split, respectively, for biasing considerations and an overlay capacitor for RF coupling. Millimeter-wave measurements at 91 GHz show that, at /spl plusmn/0.4 V bias, the separately biased subharmonic mixer requires 2-3 times less LO power than the zero-biased subharmonic mixer for the same 8 dB (SSB) conversion loss. At 180 GHz a similar LO power requirement reduction has been achieved, with a minimum conversion loss of 9.7 dB and noise temperature of 1850 K (DS8).<<ETX>>