Fabrication of voltage gated spin Hall nano-oscillators

TL;DR

This paper presents an optimized fabrication process for voltage-controlled spin Hall nano-oscillators with sub-30 nm features, enabling precise frequency tuning and dense integration for advanced spintronic applications.

Contribution

It introduces a novel fabrication method combining tilted ion beam etching and HfO_x encapsulation to improve nano-oscillator performance and scalability.

Findings

Achieved feature sizes below 30 nm with high aspect ratio.

Demonstrated 6 MHz/V frequency tunability.

Enabled dense integration of multiple gates for neural network applications.

Abstract

We demonstrate an optimized fabrication process for electric field (voltage gate) controlled nano-constriction spin Hall nano-oscillators (SHNOs), achieving feature sizes of <30 nm with easy to handle ma-N 2401 e-beam lithography negative tone resist. For the nanoscopic voltage gates, we utilize a two-step tilted ion beam etching approach and through-hole encapsulation using 30 nm HfO_x. The optimized tilted etching process reduces sidewalls by 75% compared to no tilting. Moreover, the HfO_x encapsulation avoids any sidewall shunting and improves gate breakdown. Our experimental results on W/CoFeB/MgO/SiO₂ SHNOs show significant frequency tunability (6 MHz/V) even for moderate perpendicular magnetic anisotropy. Circular patterns with diameter of 45 nm are achieved with an aspect ratio better than 0.85 for 80% of the population. The optimized fabrication process allows incorporating a large number of individual gates to interface to SHNO arrays for unconventional computing and densely packed spintronic neural networks.