Ultrafast device characterization.

Abstract

In recent years there has been tremendous progress in the development of high-bandwidth semiconductor devices, with cutoff frequencies in excess of 200 GHz becoming commonplace. Better insight into the physics of their operation requires accurate performance measurements over the complete bandwidth. Additionally, accurate measurements of device characteristics under both small-signal and large-signal conditions are necessary for successful design of high-speed integrated circuits. Conventional, purely electronic methods for characterizing the high-frequency performance of semiconductor devices include time-domain reflectometry, based on sampling oscilloscopes, and frequency-domain vector transfer function measurements, based on network analyzers. The bandwidth of these methods is limited by the electronic signal generation and measurement. Additional accuracy limitations are due to the signal generation and measurement planes being physically removed from the device under test, necessitating de-embeding procedures that suffer from connector characteristic instability and poor reproducibility between measurements. The optoelectronic time-domain sampling techniques offer a potential for a significant improvement over conventional instrumentation: the measurement planes are brought closer to the device, the interconnection parasitics are reduced or eliminated, and the measurement bandwidth is increased into the THz region. This work advances the state-of-the-art of the optoelectronic techniques in all areas pertinent to transistor small-signal and large-signal characterization: electrical signal measurement, generation and propagation. Specifically, a novel electro-optic transducer is developed and its superior bandwidth and accuracy is demonstrated. The bandwidth and power limits of the photoconductor switches for electrical signal generation are investigated using a novel epitaxially-grown GaAs-based material. A terahertz-bandwidth analytic model of coplanar microwave transmission lines is developed and experimentally verified. A large-signal digital-switching device characterization methodology is developed. The results are then used to extract the parameters and verify on picosecond time-scales a large-signal time-domain field-effect transistor SPICE model. A small-signal characterization methodology is developed and used to experimentally obtain transistor two-port frequency-domain characteristics with 100-GHz bandwidth. A large-signal microwave heterojunction bipolar transistor analysis procedure is developed and applied to the study of power saturation and nonlinearity mechanisms. The accuracy of the analysis is verified with conventional electronic instruments and with a novel hybrid optoelectronic time-domain measurement scheme.