An Investigation of HZO-Based n/p-FeFET Operation Mechanism and Improved Device Performance by the Electron Detrapping Mode

Ferroelectric field-effect transistor (FeFET) is a promising nonvolatile memory device because of its CMOS compatibility, scalability, and energy efficiency. However, the device physics has not been studied well, which hinders FeFET development and process design kit (PDK) construction. In this article, we report a comprehensive understanding of the n/p-FeFET operation mechanism as a nonvolatile memory device, for the first time, based on quasi-static split CV measurement. We also suggest a new methodology to examine the device and show the existence of excess trapped charge and the true nonvolatile polarization. Furthermore, we found that charge trapping is necessary to switch polarization in FeFET. Finally, based on our physical findings and insights, we propose a new erase mode that leads to a wider memory window and higher write endurance (> 10¹⁰ cycles), even without optimizing the device fabrication process.

I. Introduction

Ferroelectric field-effect transistor (FeFET) based on hafnium oxide has been studied for various memory-based applications, owing to its scalability, energy efficiency, and CMOS compatibility [1]–[5]. However, its accurate device physics is still not understood well, even though it is necessarily required for modeling the device, improving device performance, and constructing process design kit (PDK) to use in the industry. Many studies have focused on the interplay between polarization and charge trapping to understand the mechanism due to the high surface charge density (~10¹⁴ cm⁻²) of the spontaneous polarization in the ferroelectric layer [6], [7]. Nevertheless, the conventional methodology of measuring polarization switching has the fundamental limitation because it works only with a ferroelectric capacitor, not with FeFET. Thus, most previous studies have not directly captured the polarization value in FeFET and have not carefully studied the device based on charge analysis.