Subtractive Manufacturing for Quantum Materials

Engineering ultralow noise detectors at the Angstrom scale.

Answering fundamental questions in physics and cosmology requires continuous improvement of the noise performance of existing detector technologies as well as the development of fundamentally new types of detectors. The research group of Austin Minnich, Professor of Mechanical Engineering and Applied Physics, focuses on the solid-state physics and transport phenomena that govern the noise performance of various detectors based on semiconductor devices and superconducting circuits.

In KNI, the Minnich group develops Angstrom-scale fabrication tools for novel detector technologies. In particular, atomic layer etching (ALE) is a method that enables the subtractive manufacturing of devices with monolayer precision, providing an opportunity to fabricate devices with the same atomic precision with which original materials were grown. ALE can be roughly viewed as the inverse of atomic layer deposition in that it consists of two or more self-terminating reactions at the surface of a substrate. Unlike in ALD, ALE leads to the removal, rather than deposition, of a monolayer. In the simplest two-step process, the first step weakens the bonds at the top monolayer of a material, for instance by fluorination. The second step serves to remove this modified surface compound by volatilizing the surface, thereby removing a single monolayer per cycle in a highly controlled process. The ability to remove material with atomic precision using ALE would have a transformative impact on detector technologies and emerging quantum devices. Hence, this process is expected to be of tremendous use to the broader nanofabrication and device community.

Figure Caption:
(A) Schematic of the ALE process. The surface is fluorinated with an SF6 plasma, and the surface is then volatilized by ligand exchange to produce etching with monolayer precision. EDS image from cross-sectional TEM samples of (B) original Al and (C) ALE processed Al in a superconducting coplanar waveguide resonator, showing that the defective native oxide that causes decoherence has been replaced with a thinner film of AlF3. (D) Optical image of a fabricated coplanar waveguide resonator ready for measurement at mK temperatures.