Piezoelectric quantum 1/f noise in AlGaN HFETs and reliability

Abstract

The QED quantum 1/f noise formulas have been recently refined for the case of AlGaN/GaN HFETs and FETs through a better definition of the coherence parameter s, with much better agreement with the experiment. Indeed, for a FET/HFET width w>>L>t, this yielded s nrtLlog(w/2L) instead of the old s=2nrtw formula. Here we generalize this basic result for the first time to a finite piezoelectric case. Here L= source to drain length, t is the thickness (depth) of the channel, n is the concentration of carriers, =3.1416, and r=2.8 . 10-13 cm is the classical radius of the electron. In piezoelectric materials, particularly those also showing ferroelectric spontaneous polarization, transversal phonons are the massless quanta leading to large piezoelectric, or lattice-dynamic, quantum 1/f effects, conventional and coherent. As in the usual QED case, the parameter s' yields the observed 1/f noise as a weighted sum of conventional and coherent quantum 1/f effects. The HFET piezocoherence weighting parameter s', derived here is (gN'h/m*v s )(v s /u) 3 F(u/v s )t/12w, with N'=nLt, v s the piezophonon speed, u the drift velocity, and F(x) is a function defined earlier, equal to (2/3)x 3 for x<<1. This s' is increasing, ~t 2 , important for reliability and device optimization. For HFET stability, a slower decrease of conductivity than of polarization is found to be needed for stability along the large device width, when the temperature increases.