Engineering topics

Ma, T. P.

Publications and source records attributed to Ma, T. P..

4 records

NASA NTRS1981

Optically induced bistable states in metal/tunnel-oxide/semiconductor /MTOS/ junctions

A new switching phenomenon in metal-oxide semiconductor tunnel junction has been discovered. With a sufficiently large negative bias applied to the electrode, incident visible light of intensity greater than about 1 microW/sq cm causes the reverse-biased junction to switch from a low-current to a high-current state. It is believed that hot-electron-induced impact ionization provides the positive feedback necessary for switching, and causes the junction to remain in its high-current state after the optical excitation is removed. The junction may be switched back to the low-current state electrically. The basic junction characteristics have been measured, and a simple model for the switching phenomenon has been developed.

Lai, S. K.↗

NASA NTRS1980

Processing dependence of metal/tunnel-oxide/silicon junctions

The effects of process variations on the fixed-charge density, interface-state density, and tunneling properties of tunnel oxides on (100) silicon are discussed. Annealing the oxide in nitrogen reduces the fixed-charge and interface-state densities substantially, but also causes a marked increase in oxide capacitance. Anneals in forming gas before metallization alter the interface-state distribution and decrease the insulating qualities of the tunneling oxides. Postmetallization anneals in forming gas reduce the interface-state density to 1 x 10 to the 11th e/sq cm V or below, and appear not to affect the current through the oxide. No evidence for metal-induced interface states is observed.

Dressendorfer, P. V.↗

NASA NTRS1974

Surface-state spectra from thick-oxide MOS tunnel junctions

The conductance and capacitance of thick-oxide MOS tunnel junctions (SiO2 thickness 40 to 65 A) have been measured from 35 Hz to 210 kHz. It is demonstrated that the use of a thick-oxide MOS tunnel junction makes it possible to obtain the surface-state data throughout the whole silicon band gap with better resolution and better sensitivity than the conventional MOS capacitance techniques. A slight departure from equilibrium may occur in the voltage range where large tunnel current flows. Corrections to the energy scale must be made in this voltage range. A method for the evaluation of the junction quality is discussed. The simplified equivalent circuits necessary for the calculation of surface-state data are constructed under various bias conditions by an approach different from that used in a previously published work. The present work supports the model that at least some of the observed surface states are a consequence of the diffusion of contact metals into the oxide.

Ma, T. P.↗

NASA NTRS1974

Effect of gamma-ray irradiation on the surface states of MOS tunnel junctions

Gamma-ray irradiation with doses up to 8 megarad produces no significant change on either the C(V) or the G(V) characteristics of MOS tunnel junctions with intermediate oxide thicknesses (40-60 A), whereas the expected flat-band shift toward negative electrode voltages occurs in control thick oxide capacitors. A simple tunneling model would explain the results if the radiation-generated hole traps are assumed to lie below the valence band of the silicon. The experiments also suggest that the observed radiation-generated interface states in conventional MOS devices are not due to the radiation damage of the silicon surface.

Ma, T. P.↗