Low-frequency noise in Cr—SiO2—N-Si tunnel diodes

Low-frequency noise of Cr-SiO
2
-n-Si tunnel diodes with about 30-Å-thick oxides is investigated as function of bias, frequency, and temperature. Measurements of
1/f
noise are explained by a theory employing the two step tunneling model of Sah. Electrons from the Si conduction band are trapped by states at the Si-SiO
2
interface and then tunnel into bound states of the oxide located close to the interface. The oxide states of density N
00
can be represented by a frequency dependent parallel admittance exhibiting frequency-dependent thermal noise that modulates the dc current
I
tunneling through the oxide barrier. This generates flicker noise at the device terminals proportional to
I^{2}N_{00}
and inversely proportional to frequency
f
and tunneling area
A
. The value
A = 5
. 10
-3
A
0
, determined by fitting theoretical and experimental curves at low frequency, is only a small fraction of the gate area A
0
, since tunneling preferentially occurs through the thinnest parts of the oxide. The current
I
also exhibits full shot noise at high frequency and low current. Qualitative agreement between theoretical and measured noise is found over 9 decades. Measurements at low temperature show additional noise of generation-recombination centers at larger frequencies and currents.