Terahertz Diagnostics of SiGe Heterojunction Bipolar Transistors

We report on the first successful application of terahertz radiation to detect damage to an npn heterojunction bipolar transistor (HBT). The HBT was damaged by a voltage pulse that far exceeded its absolute maximum voltage rating. To confirm the damage, the HBT's current-versus-voltage characteristics were compared before and after the voltage pulse was applied. The two-dimensional terahertz voltage-response scans were also compared before and after the voltage pulse. Those voltage scans revealed the damage to the HBT. Unlike traditional testing techniques, the resolution of this technique is determined by the feature size of the transistor. This is a non-contact, non-invasive approach in which many transistors in a circuit can be tested, with the circuit maintained in its normal operating conditions.