Germanium Negative Capacitance Field Effect Transistors: Impacts of Zr Composition in Hf1−xZrxO2
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Germanium (Ge) negative capacitance field-effect transistors (NCFETs) with various Zr compositions in Hf1−xZrxO2 (x = 0.33, 0.48, and 0.67) are fabricated and characterized. For each Zr composition, the NCFET exhibits the sudden drop in some points of subthreshold swing (SS), which is induced by the NC effect. Drive current IDS increases with the increase of annealing temperature, which should be due to the reduced source/drain resistance and improved carrier mobility. The steep SS points are repeatable and stable through multiple DC sweeping measurement proving that they are induced by the NC effect. The values of gate voltage VGS corresponding to steep SS are consistent and clockwise IDS-VGS are maintained through the multiple DC sweeps. At fixed annealing temperature, NC device with Hf0.52Zr0.48O2 achieves the higher IDS but larger hysteresis compared to the other compositions. NCFET with Hf0.67Zr0.33O2 can obtain the excellent performance with hysteresis-free curves and high IDS.
KeywordsFerroelectric Negative capacitance Hysteresis Subthreshold swing FET
Atomic layer deposition
Boron fluoride ion
High-resolution transmission electron microscope
Metal-oxide-semiconductor field-effect transistors
Tetrakis (dimethylamido) hafnium
Tetrakis (dimethylamido) zirconium
The ferroelectric negative capacitance field-effect transistor (NCFET) with a ferroelectric film inserted into gate stack is a promising candidate for the low-power dissipation applications owing to its ability to overcome the fundamental limitation in subthreshold swing (SS) for the conventional metal-oxide-semiconductor field-effect transistor (MOSFET) . The negative capacitance (NC) phenomena in NCFETs have been extensively studied in different channel materials, including silicon (Si) [2, 3], germanium (Ge) , germanium-tin (GeSn) , III–V , and 2D materials . Also, the NC characteristics have been demonstrated in NCFETs with various ferroelectrics, such as BiFeO3 , PbZrTiO3 (PZT) , PVDF , and Hf1−xZrxO2 . Compared to other ferroelectrics, Hf1−xZrxO2 has the advantage of being compatible with CMOS integration. Experimental studies have shown that the electrical performance of NCFETs can be optimized by varying the thickness and area of Hf1−xZrxO2, which affects the matching between MOS capacitance (CMOS) and ferroelectric capacitance (CFE) [12, 13]. It is expected that the Zr composition in Hf1−xZrxO2 also has a great impact on the performance of NCFETs, because it determines the ferroelectric properties of Hf1−xZrxO2. However, there is still a lack of a detailed study on the impacts of Zr composition on the electrical characteristics of NCFETs.
In this paper, we comprehensively study the influences of the annealing temperature and the Zr composition on the performance of Ge NCFET.
Figure 1(b) shows the schematic of the fabricated NCFET. High-resolution transmission electron microscope (HRTEM) image in Fig. 1(c) shows the gate stack on Ge channel of device with Hf0.52Zr0.48O2 ferroelectric. The thicknesses of Al2O3 and Hf0.52Zr0.48O2 layers are 2 nm and 7 nm, respectively.
Results and Discussion
The impacts of the annealing temperature and Zr composition in Hf1−xZrxO2 on the electrical performance of the Ge NCFETs are experimentally studied. The stoichiometries and ferroelectric properties of Hf1−xZrxO2 were confirmed by XPS and P-V measurements, respectively. NCFETs demonstrate the steep point SS and improved IDS compared to the control device, due to the NC effect. The VTH and IDS of the Hf1−xZrxO2 NCFET are greatly affected by the annealing temperature. Multiple DC sweeping measurements show that the stability of the NC effect induced by the ferroelectric layer is achieved in NCFET. Hf0.67Zr0.33O2 NCFET can more easily achieve the hysteresis-free characteristics than the devices with higher Zr composition.
The authors acknowledge support from the National Natural Science Foundation of China under Grant No. 61534004, 61604112, 61622405 and 61874081, and 61851406. This work was also supported by the 111 Project (B12026).
Availability of Data and Materials
The datasets supporting the conclusions of this article are included within the article.
YP carried out the experiments and drafted the manuscript. YP and GQH designed the experiments. GQH and YL helped to revise the manuscript. JCZ and YH supported the study. All the authors read and approved the final manuscript.
State Key Discipline Laboratory of Wide Band Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an 710071, People’s Republic of China.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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