Negative Differential Capacitance in Low-Power Ferroelectric-FET Devices with Hf_0.5Zr_0.5O₂

INTRODUCTION

As transistors scale down, energy inefficiencies become significant due to short-channel effects and quantum tunneling. A promising solution is Negative Differential Capacitance (NDC), achieved by integrating a ferroelectric layer like zirconium-doped hafnia (Hf0.5Zr0.5O2, HZO) into the transistor’s gate stack. Our research demonstrates how HZO-enabled NDC improves the electrical performance of FETs, providing a pathway to overcome traditional scaling limits.

METHOD

HZO films were deposited using thermal Atomic Layer Deposition at 250°C with tetrakis-(ethylmethylamido) hafnium and zirconium precursors to ensure a 1:1 HfO2

ratio. Rapid Thermal Annealing at 600°C was performed to induce an orthorhombic phase transformation in the 10 nm HZO layer. The stress created between Ti/Pt electrodes and the HZO layer facilitated this phase transition.

RESULTS

NDC FETs exhibit a sub-thermionic subthreshold swing (SS < 60 mV/dec), low hysteresis (~25 mV), and minimal gate leakage (~pA). These devices outperform traditional FETs, offering low power consumption and enhanced performance. The findings highlight the potential of NDC in HZO thin films for future ultra-low-power electronics, further pushing the boundaries of transistor scaling and energy efficiency.