FuSe: Electronic-photonic heterogeneous integration for sensing above 1 THz

The goal of this project is to boost the high-frequency operating limit for conventional silicon-based semiconductor electronic devices and systems so that they can generate and detect electromagnetic radiation with frequencies above 1 terahertz (THz). Bipolar CMOS (BiCMOS) chips fabricated at silicon foundries using standard processes have been shown to generate radiation approaching, and even exceeding 1 THz. However, in general such electronic devices (e.g. semiconductor transistors, diodes) have difficulty to generate significant levels of power at such high frequencies, in part because the oscillating electrons which drive the antennas cannot travel back and forth quickly enough. However, 1 THz is a natural crossover point between electronic and photonic devices (e.g. lasers). Photonic devices are not limited by how fast free electrons move, because they generate radiation based upon a different principle: the stimulated emission of terahertz photons due to transitions of electronic between quantized energy levels. This phenomenon will be leveraged to create quantum-cascade (QC) photonic amplifiers (made of III-V semiconductors) that will amplify the weak terahertz signals generated by silicon BiCMOS electronic chips. Towards this end, novel microfabrication techniques will be used to integrate the BiCMOS electronic chips with the III-V laser chips in close proximity on a common silicon interconnect fabric. This project will culminate in the demonstration of a system that uses these terahertz signals to detect the “spectral fingerprints” of various gasses – including several which are atmospheric environmental toxins. This research addresses a grand challenge for semiconductor technology: how to extend integrated circuit semiconductor technology to fully cover the terahertz range. This application has significant societal impact, such as in environmental sensing (e.g. residential air quality, pollutant monitoring), as well as industrial/defense/aero gas sensing (e.g. for energy, propulsion, and planetary entry), and science (astrophysics, fire science, combustion). Workforce development will be organized around a robust undergraduate research program – a well-established strategy for attracting and retaining students to a discipline. A cohort of paid undergraduate researchers will be recruited, particularly focusing on incoming transfer students and departmental honors students. In addition to participation in research, they will participate in a robust professional development program, a semiconductor based academic curriculum (including microfabrication), and participation in industry internships. The goal of this project is to extend the reach of high-frequency semiconductor electronics above 1 THz by (a) developing a system for heterogeneous integration of silicon BiCMOS chips that generate THz pulses with III-V terahertz quantum-cascade (QC) laser gain material, (b) using this system to develop a hybrid THz dual-comb transmitter/receiver for multi-heterodyne spectroscopy above 1.5 THz, and (c) demonstrating this system for multi-gas sensing with applications in environmental and industrial monitoring. The approach builds upon specially designed BiCMOS frequency-comb generator chips that have been shown to emit signals up to 3 THz (albeit with low output power); these signals will then be amplified by THz QC travelling-wave power amplifiers. The intellectual merit lies first in the use of quantum-cascade photonic gain material to extend the performance of BiCMOS-foundry electronics above 1 THz. The resulting hybrid systems will exhibit the advantages of CMOS (reduced size and weight, increased integration and signal processing capability), with the power generation of III-V quantum-cascade lasers above 1 THz. Second, merit lies in the development of a terahertz silicon interconnect fabric, which will leverage advanced chiplet technology to place BiCMOS and III-V chiplets in close proximity with micron-scale alignment precision for low-loss THz interconnects. This research addresses three levels on the stack: materials (QC material development), devices (heterogeneous integration fabric, BiCMOS THz integrated circuits, and QC-amplifiers), and systems (dual-comb spectroscopy for gas sensing). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.