Monolithic integrated millimeter-wave circuits based on silicon and SiGe are emerging as an attractive option in the field of millimeter-wave communications and millimeter-wave sensors. The combination of active devices with passive planar structures, including also antenna elements, allows single-chip realizations of complete millimeter-wave front-ends. This paper reviews the state-of-the-art silicon- and SiGe-based monolithic integrated millimeter-wave circuits. The technological background as well as active and nonlinear devices and passive circuit structures suitable for silicon- and SiGe-based monolithic integrated millimeter-wave circuits are discussed. Examples of such integrated circuits and first systems applications are also presented.

Si and SiGe millimeter-wave integrated circuits

In this paper the potentiality of impact avalanche transit time (IMPATT) devices based on different semiconductor materials such as GaAs, Si, InP, 4H-SiC and Wurtzite-GaN (Wz-GaN) has been explored for operation at terahertz frequencies. Drift–diffusion model is used to design double-drift region (DDR) IMPATTs based on different materials at millimeter-wave (mm-wave) and terahertz (THz) frequencies. The performance limitations of these devices are studied from the avalanche response times at different mm-wave and THz frequencies. Results show that the upper cut-off frequency limits of GaAs and Si DDR IMPATTs are 220 GHz and 0.5 THz, respectively, whereas the same for InP and 4H-SiC DDR IMPATTs is 1.0 THz. Wz-GaN DDR IMPATTs are found to be excellent candidate for generation of RF power at THz frequencies of the order of 5.0 THz with appreciable DC to RF conversion efficiency. Further, it is observed that up to 1.0 THz, 4H-SiC DDR IMPATTs excel Wz-GaN DDR IMPATTs as regards their RF power outputs. Thus, the wide bandgap semiconductors such as Wz-GaN and 4H-SiC are highly suitable materials for DDR IMPATTs at both mm-wave and THz frequency ranges.

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Prospects of IMPATT devices based on wide bandgap semiconductors as potential terahertz sources

Basic principles of operation, fundamental power-generation capabilities, and fabrication technologies are reviewed for three groups of two-terminal devices, i.e., resonant-tunneling diodes (RTDs), transferred-electron devices (TEDs), and transit-time diodes. The paper focuses on devices for frequencies above 30 GHz, and an overview of recent research in this area and of various state-of-the-art laboratory results is given. As an outlook, the potential of some new material systems for high-power devices is discussed.

Two-terminal millimeter-wave sources

A new multifunction millimeter-wave sensor operating at 35.6 GHz has been developed and demonstrated for measurement of displacement and low velocity. The sensor was realized using microwave integrated circuits and monolithic microwave integrated circuits. Measured displacement results show unprecedented resolution of only 10 /spl mu/m, which is approximately equivalent to /spl lambda//sub 0//840 in terms of free-space wavelength /spl lambda//sub 0/, and maximum error of only 27 /spl mu/m. A polynomial curve-fitting method was also developed for correcting the error. Results indicate that multiple reflections dominate the displacement measurement error. The sensor was able to measure speed as low as 27.7 mm/s, corresponding to 6.6 Hz in Doppler frequency, with an estimated velocity resolution of 2.7 mm/s. A digital quadrature mixer (DQM) was configured as a phase-detecting processor, employing a quadrature sampling signal-processing technique, to overcome the nonlinear phase response problem of a conventional analog quadrature mixer. The DQM also enables low Doppler frequency to be measured with high resolution. The Doppler frequency was determined by applying linear regression on the phase sampled within only fractions of the period of the Doppler frequency. Short-term stability of the microwave signal source was also considered to predict its effect on measurement accuracy.

On the development of a multifunction millimeter-wave sensor for displacement sensing and low-velocity measurement

This paper studies 24-GHz automotive radar technology for detecting low-friction spots caused by water, ice, or snow on asphalt. The backscattering properties of asphalt in different conditions are studied in both laboratory and field experiments. In addition, the effect of water on the backscattering properties of asphalt is studied with a surface scattering model. The results suggest that low-friction spots could be detected with a radar by comparing backscattered signals at different polarizations. The requirements for the radar are considered, and a 24-GHz radar for road-condition recognition is found to be feasible.

Road-Condition Recognition Using 24-GHz Automotive Radar

Silicon flat profile double drift (DD) and double Read (DLHL) IMPATT diodes have been designed and fabricated, using a novel beamlead process. The goal for the design of the active layer is a maximum negative resistance of the device for a given DC power density. Experimental results are 225 mW of RF power with DD diodes and 300 mW for DLHL diodes, both in the 140 GHz range.

D-band Si-IMPATT diodes with 300 mW CW output power at 140 GHz

A multifunctional radar system for vehicles consisting of two modules with a combined bistatic/monostatic arrangement is presented. One module acts as a transceiver, whereas the other is a receiving circuit. The transmitting part radiates a frequency-modulated signal alternately in two orthogonal polarizations. The receiving parts work with different local oscillator (LO) frequencies and detect both polarizations of the scattered signal simultaneously. From the resulting Doppler spectra and a distance measurement, the velocity, tilt angle, height with respect to ground, and the direction of the movement of a vehicle can be derived. From the polarimetric information, a classification of the road condition is possible. In a first approach, the sensor was built in a conventional waveguide technique. The second step was to realize the millimeter-wave circuits of both modules with monolithic silicon millimeter-wave integrated circuit (SIMMWIC) technology. To achieve a flat arrangement, a leaky-wave antenna is developed and coupled to the SIMMWIC's.

Multifunctional radar sensor for automotive application

Synchronisation of monolithically integrated slot osciliators [1] at subharraonics of different order is investigated. With the fourth subharmonic, locking bandwidth up to 750MHz can be achieved at an osculating frequency of 71 GHz. The locking bandwidth, depending on the locking power, has been determined. The influence of a change in locking power against the position of the locking bandwidth has been examined.

Subharmonic injection locking slot oscillators

An integrated planar oscillator on a high resistivity silicon substrate generates an RF-power of 100 mW in D-band with a peak efficiency of 4.5%. The single sideband S/N ratio of the oscillator is -75 dBc/Hz@100 kHz off carrier. The investigated disc resonator with capacitive coupling to a microstrip line is manufactured by application of micromachining techniques.

High efficiency planar oscillator with RF power of 100 mW near 140 GHz

We present the first silicon-based active antenna based on flip-chip mounted Impatt diodes. Our results show that flip-chip integration of Impatt diodes is a very promising alternative to monolithic integration since expected output power and heat removal is improved significantly. Compared to active antennas based on monolithic integration, the chip size of the novel flip-chip device is reduced by a factor of 50. Due to this fact, considerable reduction of manufacturing costs is expected.

M. Wollitzer

Papers

D-band Si-IMPATT diodes with 300 mW CW output power at 140 GHz

Multifunctional radar sensor for automotive application

Subharmonic injection locking slot oscillators

High efficiency planar oscillator with RF power of 100 mW near 140 GHz

Flip-chip mounted silicon-based Impatt diodes for automotive applications