Fabricating thousands of microscopic air bridges on a single chip
Fabricating thousands of microscopic air bridges on a single chip lead image
The study of electron behavior in 1D wires gives insight into the exotic properties of electron-electron interactions. To model this scenario experimentally, Jin et al. fabricated an array of metal strips acting as gates to squeeze electrons into narrow wires just below the surface of a chip. While the theory behind 1D wires assumes infinite length, they wanted to see what would happen when such a condition is broken.
“To make short wires, we needed a way of connecting these gates together without using extra metal on the surface that would distort the 1D wires due to stray electric fields,” said author Christopher Ford. “So, we realized we needed to keep the extra metal away from the surface, forming ‘air bridges’ between the gates.”
In the end, they developed a unique process to fabricate thousands of air bridge structures, which consist of an air gap under metal bridges, on a single chip. Small numbers of air bridges already play a role in quantum-dot interference devices and superconducting microwave circuits based on coplanar waveguides.
Their process starts by spin coating the sample with three different resist layers before employing electron-beam lithography to pattern the air bridges. A higher dose of electrons exposes all three resist layers, but a lower dose exposes only the top two layers. In this way, metal evaporated on top remains as a bridge between pedestals on the surface after the resists are stripped off.
Yiqing Jin and colleagues optimized this technique to fabricate over 6,000 air bridges on the same chip.
“Ninety-five percent of devices worked perfectly” said author Pedro Vianez. As a demonstration, the paper presents experiments with 1D wires defined using an array of gates linked by approximately 400 air bridges.
Source: “Microscopic metallic air-bridge arrays for connecting quantum devices,” by Y. Jin, M. Moreno, P. M. T. Vianez, W. K. Tan, J. P. Griffiths, I. Farrer, D. A. Ritchie, and C. J. B. Ford, Applied Physics Letters (2021). The article can be accessed at http://doi.org/10.1063/5.0045557 .
