Physical science of materials

Charge accumulation and relaxation in active mode of Al/Si$_3$N$_4$/$n$-Si and Al/Si$_3$N$_4$/SiO$_2$/$n$-Si device structures

N. I. Gorbachuk^a, E. A. Ermakova^a, N. A. Poklonskii^a, S. V. Shpakovski<sup>b

a</sup> Belarusian State University, Minsk
^b JSC “INTEGRAL”

Abstract: Two MIS structures (Al/Si$_3$N$_4$/$n$-Si and Al/Si$_3$N$_4$/SiO$_2$/$n$-Si) formed on $n$-type crystalline silicon substrates grown by the Czochralski method are studied. The substrate has crystallographic orientation (100) with a resistivity of 4.5 $\Omega$ $\cdot$ cm. The layer of silicon nitride (Si$_3$N$_4$) is formed by low-pressure chemical vapor deposition (LPCVD) using a gas mixture of ammonia and monosilane. The layer of silicon dioxide (SiO$_2$) is formed by thermal oxidation of silicon in dry oxygen. The thickness of Si$_3$N$_4$ is 70 nm and the thickness of SiO$_2$ is 5 nm. The current-voltage (I–V) and capacitance-voltage (C–V) characteristics are measured, and the thermally stimulated relaxation of the charge accumulated in Si$_3$N$_4$ is studied. It is established that Al/Si$_3$N$_4$/$n$-Si structures under applied DC voltage can accumulate both positive and negative charges, while Al/Si$_3$N$_4$/SiO$_2$/$n$-Si structures can accumulate only negative charges. The accumulation of specific charge types corresponds to the dominance of monopolar injection during charge transfer in the structures. The capture of charge carriers (both electrons and holes) in traps within silicon nitride is responsible for switching processes from high electrical conductivity state to low conductivity state. During positive charge relaxation in Al/Si$_3$N$_4$/$n$-Si structures, two kinetics are observed, which is associated with the dominance of two types of traps involved in hole capture and charge transfer through the silicon nitride layer. It is shown that the presence of a silicon oxide layer enhances the thermal stability of charge stored in Si$_3$N$_4$ by introducing an additional energy barrier for electrons in Al/Si$_3$N$_4$/SiO$_2$/$n$-Si structures. It is established that within the 300–500 K temperature range, the flat-band voltage shift $\Delta U_{fb}$ induced by charge relaxation in Si$_3$N$_4$ layer does not exceed 20%. The results of this work can be used in the design of non-volatile memory cells.

Keywords: nonvolatile memory, mis structures, MNOS structures, electric charge, (C–V) characteristics.

Received: 14.07.2025
Revised: 17.08.2025
Accepted: 01.09.2025

DOI: 10.61011/JTF.2025.11.61605.179-25

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