Strongly temperature dependent ferroelectric switching in AlN, Al1-xScxN, and Al1-xBxN thin films

Abstract

This manuscript reports the temperature dependence of ferroelectric switching in Al 0.84 Sc 0.16 N, Al 0.93 B 0.07 N, and AlN thin films. Polarization reversal is demonstrated in all compositions and is strongly temperature dependent. Between room temperature and 300 C, the coercive field drops by almost 50% in all samples, while there was very small temperature dependence of the remanent polarization value. Over this same temperature range, the relative permittivity increased between 5% and 10%. Polarization reversal was confirmed by piezoelectric coefficient analysis and chemical etching. Applying intrinsic/homogeneous switching models produces nonphysical fits, while models based on thermal activation suggest that switching is regulated by a distribution of pinning sites or nucleation barriers with an average activation energy near 28 meV.

High-Temperature Ferroelectric Behavior of Al0.7Sc0.3N

“…The overall Ec results (apart from the reduced Ec values reported by Wang et al) are consistent with the literature in terms of a lower Ec due to increasing Sc content or decreasing excitation frequency. This may explain both the coincidental values between Gund et al (30% Sc, 3 kHz) and Zhu et al (16% Sc, 333 Hz) and the increased Ec for Mizutani et al (20% Sc, 100 kHz) [19][20][21][22]. Our work shows that the Pr values for Al0.7Sc0.3N remained relatively stable up to 400 °C (Figure 3d).…”

“…The increasing leakage with temperature is important for compensation when possibly measuring changes in polarization (e.g., during retention testing). [19][20][21][22]. Our work shows that the P r values for Al 0.7 Sc 0.3 N remained relatively stable up to 400 • C (Figure 3d).…”

“…Polarization−electric field (P-E) hysteresis loops were collected between probe station temperatures of 23−400 • C using an excitation frequency of 10 kHz. This frequency was chosen to reduce the leakage contribution to the P r values, and 10 kHz is a relatively high frequency when compared to previous reports on ferroelectric AlScN, which range between 333 Hz and 100 kHz [19,21]. Retention testing was used to measure the stability of a polarization state over time to inspect the volatility of that state.…”

“…While this high E c is problematic for integration with low−voltage devices, it can be valuable for retention characteristics as temperatures increase [8]. The E c of AlScN can be tuned through various modifications such as composition [14][15][16], stress [17], epitaxial alignment [18], and temperature [19][20][21][22]. In addition to thickness scaling, these trends are important for integrating AlScN into a high−temperature chip to reduce the operating voltages.…”

Effect of Substrate-RF on Sub-200 nm Al0.7Sc0.3N Thin Films

“…While a few works addressed the latter issue [16,17], several groups demonstrated how it is possible to reduce the coercive field by acting on either the AlScN structure or on the experimental set-up. A higher Sc-content [10], higher crystallinity [18], the use of different substrates [19], and testing-temperature [20] have been proven to reduce the voltage needed to switch, while still maintaining large polarization values. Another effective tuning parameter is represented by the residual bulk stress on the film, which can be controlled though different process parameters, such as pressure, N 2 /Ar ratio, or substrate bias [21][22][23].…”