Imprinted hafnia antiferroelectric-dielectric heterojunction and high CDE/CFE structure for energy efficient transistor

Abstract

High-capacity capacitors are essential for many electronic devices, including cell phones, computers, digital TVs, and electric vehicles. Previously, higher dielectric constant materials were used or reduced dielectric thickness to achieve greater capacitance (charge). It has been recognized that this existing strategy consists of a very thin, high dielectric constant layer of dynamic random access memory capacitors and high-performance logic transistors. However, this approach is no longer compatible with the extreme miniaturization and low operating voltage trends found in future electronic devices, requiring radical alternatives. Accordingly, exploiting the negative capacitance (NC) effect of ferroelectric materials has emerged as a possible solution for low-power transistor devices and high-charge-density capacitors, and is emerging as an attractive competitor in solving this problem. However, although steep switching characteristics (subthreshold swing < sub-60 mV/dec) have been demonstrated in various devices combining conventional transistors and ferroelectric gates, the practical application of the NC effect is still somewhat problematic due to the inherent hysteresis problem. Therefore, in order to confirm the unstable NC effect, a study using a dielectric/ferroelectric (DE/FE) laminated film with an added dielectric layer that can receive boosting and stabilize the W-shape of internal energy vs electrical polarization(U-P) to a U-shape is in progress. In this paper, we report on transient NC effects through an amorphous-Al2O3/polycrystalline-Hf0.25Zr0.75O2(HZO) bilayer system prepared using atomic layer deposition. The ferroelectric thin film processing conditions were carefully adjusted to align the dipoles to one side, a prerequisite for examining the transient NC effect by creating a positive fixed charge on top through post-deposition-annealing(PDA). In the case of the dielectric thin film, the focus was on suppressing the leakage current to prevent charge injection that suppresses the NC effect. Capacitance boosting was observed depending on the dielectric and ferroelectric thicknesses in the Al2O3/Hf0.25Zr0.75O2 bilayer thin film using the short-pulse type. Furthermore, we study hafnia ferroelectric field effect transistors using an optimized ferroelectric layer showing NC effect. We studied a ferroelectric field effect transistor of a structure including a floating gate (metal-halfnia ferroelectric-metal-gate oxide-silicon) using a short-pulse type, and improved the operating voltage at the point where the NC effect occurs by controlling the capacitance of ferroelectric and gate oxide film. Through this, the NC effect of the hafnia-based ferroelectric thin film was confirmed and the subthreshold swing of sub-60 mV/dec was verified.