Load-Pull Characterization at G-band: an Insight on BiCMOS 55nm Technology

The 55nm BiCMOS technology, manufactured by STMicroelectronics, shows great potential for applications in the mm-wave and sub-mm-wave frequency ranges. It features a heterojunction bipolar transistor (HBT) with characteristic frequencies, ft and fmax, of 320 and 370GHz respectively. Its development involves lengthy manufacturing and validation processes. In this work, the aim is to develop a load-pull characterisation bench at frequencies above 140GHz. The realisation of this bench is still limited by the power performance of the sources, detectors and impedance synthesizers available on the market. Through the state-of-the-art of solutions previously realized, a hybrid solution is proposed. The source, similar to the architecture of a VNA extension head, as well as the detectors are kept off-wafer for a perennial use of the measurement bench. Particular attention is given to the calibration steps, during which the difficulty of scalar measurement at mm-wave frequencies is highlighted. In addition, the impedance tuner is integrated on-chip with the HBT in order to avoid the losses of the RF probe. This tuner is designed in the BiCMOS 55nm technology. The number of control voltages is deliberately minimised in order to allow for long-term use in a box. An innovative architecture is also presented. In parallel, an automation program is implemented to improve the measurement accuracy, perform the calculation of the component parameters and reduce the measurement time.