Dielectric relaxation in hafnium oxide: A study of transient currents and admittance spectroscopy in HfO2 metal-insulator-metal devices

Abstract

Dielectric relaxation is studied in 10 nm HfO2 thin films which are deposited by atomic layer deposition on TiN and Pt electrodes. Transient currents are recorded from 10−3 s to 10 s, as a function of bias (0.1 V to 1 V) and temperature (20 °C to 180 °C). A Curie-von Schweidler law is observed, I = Q0/tα. The power law exponent α is constant with bias and strongly depends on the temperature (varying in the 0.65–1.05 range, with a peak at 75 °C). The amplitude Q0 is described by a relation of the form Q0 = C0Vβ, where the factor C0 is weakly activated and the exponent β varies with temperature (in the 0.9–1.5 range as T varies). Transient currents are discussed along with tunneling based models from the literature. To complement transient current experiments, admittance spectroscopy (conductance G and capacitance C) is performed at low frequencies, from 0.01 Hz to 10 kHz. The dispersion law of the conductance is of the form G ∼ ωs. The capacitance is the sum of two terms, a non-dispersive term (C∞) and a low-frequency dispersive term, CLF ∼ ω−n. The critical exponents s and n verify s ≈ α and n ≈ 1−α. At room temperature, the dielectric constant is expressed as ɛ′ = Δɛ′ f−n + ɛ′∞, where ɛ′∞ = 11.1, n ≈ 0.2/0.3 (Pt/TiN), and Δɛ′ ≈ 1.5/0.7 (Pt/TiN).