A physical model for random telegraph signal currents in semiconductor devices

TLDR

McWhorter’s 1/f noise model attributes low‑frequency noise in MOSFETs to Lorentzian spectra from trap‑induced current modulation, and recent evidence supports this mechanism. The authors aim to develop a comprehensive model that explains the generation of random telegraph signal (RTS) waveforms in semiconductor devices. They derive RTS amplitude modulation using an extension of Ramo’s theorem, calculate characteristic times from trap properties, carrier concentrations, and temperature, and apply the model to BJTs, JFETs, and MOSFETs while addressing limitations of standard capture formulas. Experimental studies confirm that RTS amplitudes and characteristic times depend on device geometry, bias, and temperature, validate the model, and show that intrinsic carrier concentration dominates the characteristic times in weak‑inversion MOSFETs.

Abstract

The model proposed by McWhorter for low-frequency noise in metal-oxide-semiconductor field-effect transistors (MOSFETs) assumed that the 1/f spectrum was due to the sum of the Lorentzian spectra produced by modulation of the channel current by charge state transitions at traps in the adjacent oxide. Considerable evidence for the presence of such current modulation has been accumulated recently. From extensive studies of random telegraph signal (RTS) current waveform in many types of devices we present new results on the dependence of the amplitudes and characteristic times on device geometry, bias, and temperature. Based on these results we propose a comprehensive model for the generation of RTS waveforms in semiconductor devices. The amplitude modulation of a steady current in a device due to the trapping of a carrier at a fixed site is derived by applying an extension of Ramo’s theorem. The characteristic times of the RTS are derived from the properties of the trap, the carrier concentrations, and temperature. The model is applied to the analysis of RTS waveforms in bipolar junction transistors , junction field-effect transistors, and MOSFETs. Experimental results on the dependence of the RTS characteristics on bias and temperature provide validation of the model. It is shown that the intrinsic carrier concentration plays a dominant part in determining the characteristic times in a MOSFET in weak inversion. The problems associated with the application of standard formulas for capture when there is no spherical symmetry around the trap are discussed.