Reliability of HfO₂-Based Ferroelectric FETs: A Critical Review of Current and Future Challenges

Abstract

Ferroelectric transistors (FeFETs) based on doped hafnium oxide (HfO2) have received much attention due to their technological potential in terms of scalability, high-speed, and lowpower operation. Unfortunately, however, HfO2-FeFETs also suffer from persistent reliability challenges, specifically affecting retention, endurance, and variability. There is a broad consensus that a deep understanding of the reliability physics of HfO2-FeFETs is an essential prerequisite for the successful commercialization of this promising technology. In this paper, we review the current understanding of the relevant reliability aspects of HfO2-FeFETs. We initially focus on the reliability physics of ferroelectric capacitors, as a prelude to a comprehensive analysis of FeFET reliability. Then, we interpret key reliability metrics of the FeFET at device-level (i.e., retention, endurance, variability) based on the physical mechanisms previously identified. Our integrative theoretical framework connects apparently unrelated reliability issues and suggests mitigation strategies at either device, circuit, and system level. We conclude the paper by proposing a set of research opportunities to guide future development in this field.

An Aqueous Route to Oxygen-Deficient Wake-Up-Free La-Doped HfO2 Ferroelectrics for Negative Capacitance Field Effect Transistors

“…However, quantitatively, simulations predict a much larger improvement for the HLO NCFET compared to that of the Al 2 O 3 MOSFET for both SS and I ON . This could be due to the charge mismatch between the electron density in the IGZO layer and the polarization charge on the HLO, which in general is caused by (i) a large fraction of polarization charge being screened by traps in the gate stack and (ii) the HLO operating in a nonsaturated P–E loop. , In the simulated devices instead, the electrical connection between the Al 2 O 3 MOSFET gate and the HLO layer forces the IGZO charge and the polarization to be balanced, hence leading to an enhanced NC effect. In this sense, simulation results need to be interpreted as maximum theoretical limits of the HLO NCFET, assuming that the polarization charge is fully screened by the channel electron density and that the ferroelectric operates in the saturated P–E loop.…”

Enhancing Memory Window Efficiency of Ferroelectric Transistor for Neuromorphic Computing via Two‐Dimensional Materials Integration

“…[27][28][29][30] The performance of FeFETs is significantly affected by the properties of the ferroelectric material, such as leakage current, interface trap density, memory window, C2C variation, retention, and endurance. [16][17][18][19][20] Therefore, it is crucial to establish a comprehensive understanding of the ferroelectric material used in the gate stack of the Fe-FET. To achieve this, we synthesized various thicknesses of HZO (10,15,20, and 35 nm) using the protocol outlined in our previous work.…”

“…Figure 2h shows the endurance of the device up to 20 000 cycles with negligible degradation in the perspective of the drain current on-off ratio. These high performances of the FeFET are contributed by the improvement in the following aspects [9,16,19,20] : low level of leakage current in the device (Figure S8, Supporting Information), thanks to the decreased oxygen vacancies in the HZO layer; the high charge carrier density and mobility of the 2D MoS 2 [22,23] ; reduced charge trapping at the interface of MoS 2 and Al 2 O 3 because of the sharp interface revealed in Figure 2b; and the mitigated depolarization field and hence deterrence of the severe degradation of the insulating layer under strong electric field with the tunability of A OX /A FE in the MFMIS structure as discussed in the next section.…”

“…The development of FeFETs is accompanied by three significant challenges that must be addressed. [16][17][18][19][20] The first challenge is achieving a clean interface between the semiconductor and the ferroelectric, which is crucial for the performance of the device. Second, to ensure at least ten years of data retention, it is necessary to avoid a large depolarization field, as the large permittivity in series with the semiconductor's depletion layer is unfavorable.…”

First direct observation of the built-in electric field and oxygen vacancy migration in ferroelectric Hf0.5Zr0.5O2 film during electrical cycling

“…[8][9][10][11][12][13][14] This theory suggests that the wake-up (fatigue) effects arise from the change of the local electric field due to the migration of charged defects, especially oxygen vacancies, leading to the depinning ( pinning) of the domain walls and an increase (decrease) in the number of switchable domains. [15][16][17] The other theory suggests that the magnitude of remanent polarization (P r ) is mainly affected by the fraction of the polar orthorhombic phase (o-phase). Accordingly, the wake-up and the fatigue effects are caused by an increase and decrease in the polar o-phase, respectively, as driven by the field-induced phase transition during the electrical cycling.…”