Publication Date

8-1-2025

Date of Final Oral Examination (Defense)

4-25-2025

Type of Culminating Activity

Dissertation

Degree Title

Doctor of Philosophy in Electrical and Computer Engineering

Department

Electrical and Computer Engineering

Supervisory Committee Chair

Jim Browning, Ph.D.

Supervisory Committee Member

Kurtis Cantley, Ph.D.

Supervisory Committee Member

Benjamin C. Johnson, Ph.D.

Abstract

Silicon-based Gated Field Emitter Arrays (Si-GFEAs) are among the most well-developed field emitters. They are being actively explored for vacuum transistors and microwave vacuum electron devices due to their high-frequency performance, radiation resistance, and thermal stability up to 400 °C. However, their long-term reliability is limited by sudden failure events, resulting in cathodic vacuum arcs. This dissertation presents a combined experimental and simulation-based investigation into arc initiation mechanisms in Si-GFEAs. Different device arrays were tested under normal operation in vacuum at 10^-7 Torr with gate voltages of 50-70 V and emission currents from tens of nA to tens of µA. The arcs generate a voltage transient measured by an oscilloscope. Untreated devices showed time to arc of tens of minutes while vacuum baked devices (400°C) showed 50% longer arc times indicating desorbed gas is important in the arc initiation mechanism. Devices were also tested under different gas environments (nitrogen and argon) and pressures ranging from 10^⁻⁷ to 10^⁻⁴ Torr. Above 10^-4 Torr, the time to arc dropped dramatically to tens of seconds. Even devices that emitted no current or were operated in reverse bias arced in tens of seconds. This result strongly suggests vacuum dielectric surface breakdown due to adsorbed gas on the surface creating surface leakage as the initiation mechanism rather than field emission current. Simulations using particle tracking and electrostatic Particle-in-Cell (Es-PIC) solvers were performed to analyze the effects of electron impact ionization on neutrals in the test chamber and on the collector anode. The trajectory analysis looked at ion bombardment of the tip apex and of the dielectric surface adjacent to the emitter tip shaft. Results revealed that surface charge build-up on the dielectric—reaching densities of up to 1.7 C/m^² under high emission current and low vacuum conditions—exceeding surface charge density threshold 4µC/cm^2, sufficient to trigger surface flashover within tens of minutes of operation. Analytical models of emission beam spreading showed that overlapping emission from neighboring tips contributes significantly to charge accumulation on that dielectric ring. Overall, this work identifies surface breakdown—driven by dielectric charging as the primary failure mechanism in GFEAs. These findings offer critical insights into arc initiation mechanisms informing future design strategies for these devices.

Comments

Rushmita Bhattacharjee, ORCID: 0009-0008-7349-6904

DOI

https://doi.org/10.18122/td.2413.boisestate

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