UPS: According to low temperature measurement, HBTs showing already values of fT / fMAX = 270 / 400 GHz at 300 K can be improved for instance to 306 / 500 GHz by reducing more the base-collector capacitance, the base resistance and the transit time, all by 12%. The enhanced reverse Early effect can be a limiting factor at low temperature where the current gain falls dramatically at maximum fT and fMAX. At 30 K, a loss of about 7% can be estimate for fMAX = 360 GHz in some HBTs (18% for fT). fMAX record value of 500 GHz at 300 K shows an 50% increase at 30 K with a record value of 750 GHz.
IMS: Development of On-Si calibration procedure:
Comparing different calibration (SOLT, TRL) methods gives similar results. Furthermore the on-Si calibration brings the following advantages: (i) it calibrates the system in one step, thus significantly reducing the calibration time, (ii) using appropriate test structures, no additional de-embedding is necessary, (iii) detailed equivalent circuits of backend parasitics are not required anymore, (iv) possible distributed behaviour of backend parasitics has no impact on calibration accuracy, and (v) calibration and measurement are done in the same environment that permits the correction of coupling phenomena between wafer surface and probe tips. We expect that this method will obviate the regular ISS cal substrate.