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 degrees 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.