Non-ohmic conduction in MOS systems with thin oxide layers

Grünler

1977

Phys. Stat. Sol. (a)

Current density—fieldstrength characteristics of MOS structures with thermally grown SiO2 and undoped and with arsenic doped pyrolytic SiO2 are measured. The results show that there exist different ranges of current conduction which could be refered to typical energy distributions of bulk trap density within the insulator. In this way tunnel hopping range at lower fields strengths, Poole‐Frenkel behaviour, and Fowler‐Nordheim range could be understood very well. Looking to de current behaviour, inhomogeneities of the trap density within SiO2 layers are to be taken into account as the normal case of such layers.

DC current-voltage behaviour of SiO2 layers

Grünler

1977

Phys. Stat. Sol. (a)

Tunnel hopping current and trap filling in insulating layers

1979

Phys. Stat. Sol. (a)

The differential equation of trap filling with detrapping is solved at the case of tunnel hopping current conduction in insulating layers. The time dependent de current at constant field is shown to give the average values of time constants τ of tunnel hopping transitions, trap distances xt, and trap densities Nt. Increasing the field step by step one obtains a raw feature of the energy distribution of trap density above the Fermi level. Observation of two well separated time constants indicates strong interface region trap filling. The derived method is limited by the change from tunnel hopping to band conduction.

DC Characteristics of MOS Structures and Hopping Currents in Thermally Grown SiO2 Films

1982

phys. stat. sol. (a)

DC characteristics of thermally grown SiO2 films of thicknesses between 70 and 120 nm in MOS structures are measured from below 106 V/cm to breakdown. The measuring conditions and the significance of the measured currents are derived from a model of spatial trap distribution which suggests interface regions of higher trap density compared with the bulk. At some samples nearly exact Fowler‐Nordheim characteristics are found whereby the current did not show any measurable decrease with time indicating the SiO2 films to have very low trap density. In the range of field strengths below Fowler‐Nordheim conduction on many samples currents are measured which are in good accordance with j ∼ exp (–B/F1/4). This behaviour is derived by the percolation theory of hopping conduction in amorphous solids. It is suggested that real percolation channels exist in SiO2 films which may be influenced during the preparation of the films. The hopping currents tend to instabilities under electrical stress.