Matthew F. Bauwens

Terahertz Micromachined On-Wafer Probes: Repeatability and Reliability

An improved micromachined on-wafer probe covering frequencies 500-750 GHz is demonstrated in this paper to address sub-millimeter-wave integrated-circuit testing. Measurements of a prototype WR-1.5 micromachined on-wafer probe exhibit a return loss better than 12 dB and a mean insertion loss of 6.5 dB from 500 to 750 GHz. The repeatability of on-wafer measurements with the micromachined probe is investigated. Monte Carlo simulations are used to identify the dominant error source of on-wafer measurement and to estimate the measurement accuracy. The dominant error source is positioning error, which results in phase uncertainty. Reliability tests show the probe is robust and can sustain over 20 000 contacts.

Design and Characterization of Integrated Submillimeter-Wave Quasi-Vertical Schottky Diodes

This work reports on a new approach to realizing vertically oriented Schottky diodes, with ohmic contact formed directly below the anode, that can be readily integrated into planar millimeter and submillimeter-wave circuits. The diode structure is based on backside processing and bonding of the diode epitaxy to a host, high-resistivity silicon substrate that supports both the vertical diode and its associated circuitry. A set of prototype diodes of different anode diameters are fabricated for characterization at both dc and (for the first time) submillimeter-wave frequencies (325-750 GHz) using micromachined on-wafer probes. Device equivalent circuit parameters extracted from these measurements are in good agreement with those expected from fundamental Schottky barrier diode theory and indicate the vertically oriented diodes yield series resistance values that are comparable to or lower than planar-oriented diodes of similar dimensions.

A 1.1 THz micromachined on-wafer probe

This paper presents a micromachined probe for on-wafer measurements of circuits in the WR-1.0 waveguide band (0.75 - 1.1 THz). The probe shows a measured insertion loss of less than 7 dB and return loss of greater than 15 dB over most of the band. These are the first reported on-wafer measurements above 1 THz.

160 GHz Balanced Frequency Quadruplers Based on Quasi-Vertical Schottky Varactors Integrated on Micromachined Silicon

This work reports on an integrated frequency quadrupler operating at 160 GHz with maximum efficiency of 30% and corresponding output power of 70 mW. The quadrupler design includes two frequency doubler stages in cascade and is based on a balanced circuit architecture that addresses degradation issues often arising from impedance mismatches between multiplier stages. A unique quasi-vertical diode fabrication process consisting of transfer of GaAs epitaxy to a thin silicon support substrate is used to implement the quadrupler, resulting in an integrated drop-in chip module that incorporates 18 varactors, matching networks and beamleads for mounting. The chip is tailored to fit the multiplier waveguide housing, resulting in high reproducibility and consistency in manufacture and performance. Estimates of the varactor temperature for the multiplier were made using the diodes as integrated thermometers. These measurements estimate the operating temperature of the varactors in the quadrupler input stage to be 35 °C.

Improved Micromachined Terahertz On-Wafer Probe Using Integrated Strain Sensor

This paper introduces an improved method for monitoring and controlling the contact condition of terahertz on-wafer probes to enhance the measurement repeatability as well as probe lifetime. This method enables accurate contact force and contact angle measurements without modification to the standard probe station. Both probe contact force and contact angle are crucial for RF measurement repeatability. Repeatable probe contact force can be achieved by properly monitoring and controlling the strain generated at designated positions on the terahertz probe due to probe deformation induced by contacting the test substrate. Contact angle can be measured by asymmetrical strain on symmetrical positions of the probe when the probe is contacting the test substrate with angular misalignment. In this work a WR-1.5 (500 GHz-750 GHz) probe with integrated strain sensor is developed and tested. Mechanical tests show that the integrated sensors have a contact force resolution of 0.2 mN and a contact angle resolution of 0.05° about the center. RF tests show that repeatable measurements can be achieved with 3 mN contact force after adjusting probe contact angle using the integrated sensors, as compared to a previously reported value of 15 mN.

An Experimental Technique for Calibration Uncertainty Analysis

An experimentally based technique for characterizing calibration uncertainty is presented. The approach described calculates uncertainty metrics at the output of the calibration processing chain as opposed to the input. In doing so, this method replaces the complexities of error propagation with the computational effort associated with performing numerous calibrations. Practical applications are demonstrated for a variety of scenarios focused on one-port calibration, illustrating the versatility of the technique. An open-source implementation has been made publicly available as part of the Python module scikit-rf.

A W-band balun integrated probe with common mode matching network

There has been a growing interest in developing differential Millimeter-wave Monolithic Integrated Circuits (MMICs) in recent years. The characterization infrastructure for these differential devices however, is still limited at higher frequencies. In this paper, a balun integrated probe is designed to cover the entire W-band (75 - 110 GHz) with the potential to be scaled to even higher frequencies. Test structures of the balun are characterized and found to agree well with simulated results for the entire W-band, while the balun integrated probe is characterized from 90 to 115 GHz, also agreeing well with simulation. Over the frequency range measured, the balun integrated probe has lower than -22 dB coupling between the single-ended input and common mode output, as well as between the common and differential modes. Furthermore, the return loss for the differential output and single-ended input modes are better than 10 dB, while the common mode return loss is also better than 10 dB.

Characterization of Micromachined On-Wafer Probes for the 600–900 GHz Waveguide Band

A micromachined on-wafer probe has been designed to facilitate the development of integrated circuits in the 600-900 GHz frequency range. The probe tip is fabricated on a 5-micrometer thick high-resistivity silicon substrate using a silicon-on- insulator fabrication process. This letter updates previous work on WR-1.2 wafer probes and presents for the first time the full RF characterization of the probe. These are the first reported on-wafer measurements above 750 GHz.

A W-Band Micromachined On-Wafer Probe With Integrated Balun for Characterization of Differential Circuits

Differential circuits are commonly used for millimeter-wave monolithic integrated circuits such as amplifiers and voltage-controlled oscillators. The infrastructure for their characterization, however, remains limited at these frequencies. With the recent development in micromachined on-wafer probes, a probe integrated with balun circuitry can provide a convenient way to characterize differential integrated circuits. In this paper, a micromachined probe with an integrated balun operating at W-band is demonstrated. The measured S-parameters of the balun probe are in agreement with simulation and meet the design performance requirements. Furthermore, the balun probe design has the potential to be scaled to submillimeter-wave frequencies.

Integrated strain sensor for micromachined terahertz on-wafer probe

This paper introduces an improved method for monitoring and controlling the contact condition of terahertz on-wafer probes. This method enables accurate contact force measurement without modification to the standard probe station. Repeatable probe contact force is crucial for RF measurement repeatability and can be achieved by properly monitoring and controlling the strain generated at designated positions on the terahertz probe due to probe deformation induced by contacting the test substrate. A WR-1.5 (500 GHz-750 GHz) probe with integrated strain sensor is developed and tested. Measurement results of the WR-1.5 probe using 11 mN contact force controlled separately by load cell and strain sensor are presented.