COMPARISON OF 1/f NOISE IN JFETs AND MOSFETs WITH SEVERAL FIGURES OF MERIT

Abstract

Measurement results are presented from 0.1 Hz to 100 kHz of 1/f and thermal noise in different n-JFETs, and n- and p-MOSFETs. The comparison of the 1/f noise is based on Hooge's empirical relation with the 1/f noise parameter α as figure of merit, without suggesting a physical origin. We find that the empirical relation for 1/f noise in MOSFETs and JFETs can be used as a tool to pinpoint the dominant noise source (either ΔN number fluctuations or Δμ mobility fluctuations) and its location, either in the channel or in the parasitic series resistance. Similar relations hold in JFETs and MOSFETs for the 1/f noise corner frequency fc, where thermal and 1/f noise are equal and the ratio fc/fT with fT the unity current gain frequency. The geometry independent parameter α and ratio fc/fT are compared from MOSFETs and JFETs with different channel width (W) and length (L). The results show that very low-noise n-JFETs have a corner frequency fc ≈ 40 Hz, and very low 1/f and thermal noise in agreement with the high W/L ratio and high area WL of the device. Specifically, the equivalent input noise voltage of the investigated JFET IF9030 was about 3.7 nV/√ Hz at 1 Hz, 1.3 nV/√Hz at 10 Hz, and about 0.6 nV/√ Hz (3.6 ×10-19 V2/Hz or Req th noise = 23 Ω) for f ≥ 100 Hz. The 1/f noise parameter α for that JFET is as low as α = 2 × 10-8. This α-value is among the lowest values ever observed. MOSFETs often have α, fc and fc/fT values that are a few decades higher than for JFETs.