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

Low-frequency noise of Cr-SiO2-n-Si tunnel diodes with about 30-Å-thick oxides is investigated as function of bias, frequency, and temperature. Measurements of 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-SiO2interface and then tunnel into bound states of the oxide located close to the interface. The oxide states of density N00can be represented by a frequency dependent parallel admittance exhibiting frequency-dependent thermal noise that modulates the dc current tunneling through the oxide barrier. This generates flicker noise at the device terminals proportional to and inversely proportional to frequency and tunneling area . The value . 10-3A0, determined by fitting theoretical and experimental curves at low frequency, is only a small fraction of the gate area A0, since tunneling preferentially occurs through the thinnest parts of the oxide. The current 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.