Design of a Terahertz InP HBT Quadrupler and Silicon Interposer

This work details the design and characterization of a terahertz (THz) frequency quadrupler in a 250 nm Indium Phosphide (InP) heterojunction bipolar transistor technology (HBT) $\left(f_{t} / f_{\text {max }} 350 / 600 \mathrm{GHz}\right)$ with output at 580 GHz. The design uses coupled lines to optimize loss, matching and output power. Next, this work first details the fabrication of a custom silicon interposer than can be used on integrated circuits with soft dielectrics that are difficult to reliably wirebond to. Compared to prior art, we describe a single structure that can be used to interface the die to a PCB for low speed connections. This technique does not require additional processing like recessing in a newer structure, and can be adapted to fit any configuration of pads. The technique is hence amenable to package radio-frequency integrated circuit (RFIC) designs that include on-chip inductors, and that need careful consideration to the environment in the vicinity of the inductors. The intervening structure is also shorter compared to conventional wirebonds. This interposer technique has the potential to be further extended to provide reliable connections at radio frequency (RF), and is the topic of current research. The interposer detailed is used to provide bias connections to the chip. Quadrupler S-parameter and large signal characterization results, and correlation with simulations are discussed next.