C-V and I-V characteristics of ultrathin-oxide MOS structures: Identification and analysis

Abstract

Listen

Translate article

For an NMOS structure with 3.7-nm-thick oxide, dynamic I-V characteristics are digitally measured by applying an upward and a downward gate-voltage ramp. An averaging procedure is employed to deduce the tunneling (active) current component and the quasi-static C-V characteristic (CVC). Analyzing the depletion segment of the CVC provides reliable values of the semiconductor doping level, the oxide capacitance and thickness, and the sign and density of oxide-fixed charge, as well as estimates of the dopant concentration in the poly-Si region. These data are used to identify the Ψs(V g), V i(V g), and I t(V i) characteristics, where Ψs is the n-Si surface potential, V i is the voltage drop across the oxide, V g is the gate voltage, and I t is the tunneling current; the gate-voltage range explored extends to prebreakdown fields (∼13 MV cm−1). The results are obtained without recourse to fitting parameters and without making any assumptions as to the energy spectrum of electrons tunneling from the n-Si deep-accumulation region through the oxide. It is believed that experimental I t-V i and Ψs-V g characteristics will provide a basis for developing a theory of tunneling covering not only the degeneracy and size quantization of the electron gas in the semiconductor but also the nonclassical profile of the potential barrier to electron tunneling associated with the oxide-fixed charge.