SEBAT-Based Readout for FET THz Detectors With Intrinsic Power-to-Frequency Conversion

Abstract

TeraHertz (THz) detection with Field-Effect Transistor-based (FET-based) detectors requires low-noise amplification, which typically involves trade-offs in terms of complexity, power, and area, resulting in severe scalability constraints for pixel integration into imaging arrays. The purpose of this paper is to describe a novel approach, from design to experimental validation, that enables active device-level amplification of the signal generated by a FET detector and converts it to a frequency suitable for digital processing. This has been done by exploiting a Single-Electron Bipolar Avalanche Transistor (SEBAT) to build a low-noise compact front-end circuit. The FET output is connected to the SEBAT forming a circuit element that here is defined as a TeraHertz Single-Electron Transistor (THzSET). The FET generates a detection current when it senses the THz signal; this current is then injected into the SEBAT, which generates an avalanche current pulse for each single electron, achieving a device-level amplification. The avalanche pulse rate is then evaluated from the signal measured at the SEBAT collector, and performing an FFT of the counts-per-second curve over time it is possible to measure the modulated THz signal applied to the device. The obtained Responsivity <inline-formula> <tex-math notation="LaTeX">$\text {R}_{\text {F}}$ </tex-math></inline-formula> and the Noise Equivalent Power NEP are respectively <inline-formula> <tex-math notation="LaTeX">$\frac {\text {4.61Gcps}}{\text {W}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$\frac {\text {88nW}}{\sqrt {\text {Hz}}} $ </tex-math></inline-formula> at 330GHz illumination frequency. This is achieved with sub-<inline-formula> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> power consumption and minimal area overhead: indeed, the pixel and the interface have a total area of 0.146mm², where the antenna area is <inline-formula> <tex-math notation="LaTeX">${455} \times {320}\mu \text{m}^{{2}}$ </tex-math></inline-formula> and the SEBAT area is <inline-formula> <tex-math notation="LaTeX">${27} \times {22}\mu \text{m}^{{2}}$ </tex-math></inline-formula>.