Current status of ferroelectric-gate Si transistors and challenge to ferroelectric-gate CNT transistors

Hiroshi Ishiwara 한국물리학회 2009 Current Applied Physics Vol.9 No.11

Current status of ferroelectric-gate FETs (field effect transistors) is reviewed. First, characteristics of Si FETs with MFIS (metal–ferroelectric–insulator–semiconductor) gate structures are discussed. It has been shown that the data retention characteristics of ferroelectric-gate FETs are much improved by use of HfO2-based buffer layers which are inserted between the ferroelectric-gate film and Si substrate for preventing inter-diffusion of constituent elements. Then, usefulness of organic ferroelectrics such as copolymers of vinyliden fluoride and trifluoroethylene (P(VDF–TrFE)) in fabrication of MFIS devices is demonstrated. In an Au/P(VDF–TrFE)/Ta2O5/Si MFIS diode, a memory window as wide as 2.9 V has been obtained with a voltage sweep of ±4 V. Finally, operation mechanisms in ferroelectric-gate CNT (carbon nano-tube) transistors are discussed, assuming Schottky barrier conduction at the source and drain contacts. Current status of ferroelectric-gate FETs (field effect transistors) is reviewed. First, characteristics of Si FETs with MFIS (metal–ferroelectric–insulator–semiconductor) gate structures are discussed. It has been shown that the data retention characteristics of ferroelectric-gate FETs are much improved by use of HfO2-based buffer layers which are inserted between the ferroelectric-gate film and Si substrate for preventing inter-diffusion of constituent elements. Then, usefulness of organic ferroelectrics such as copolymers of vinyliden fluoride and trifluoroethylene (P(VDF–TrFE)) in fabrication of MFIS devices is demonstrated. In an Au/P(VDF–TrFE)/Ta2O5/Si MFIS diode, a memory window as wide as 2.9 V has been obtained with a voltage sweep of ±4 V. Finally, operation mechanisms in ferroelectric-gate CNT (carbon nano-tube) transistors are discussed, assuming Schottky barrier conduction at the source and drain contacts.

강유전체를 이용한 음의 정전용량 무접합 이중 게이트 MOSFET의 문턱전압 모델

정학기 ( Hakkee Jung ) 한국전기전자재료학회 2023 전기전자재료학회논문지 Vol.36 No.2

An analytical threshold voltage model is presented to observe the change in threshold voltage shift ΔV_th of a junctionless double gate MOSFET using ferroelectric-metal-SiO₂ as a gate oxide film. The negative capacitance transistors using ferroelectric have the characteristics of increasing on-current and lowering off-current. The change in the threshold voltage of the transistor affects the power dissipation. Therefore, the change in the threshold voltage as a function of theferroelectric thickness is analyzed. The presented threshold voltage model is in a good agreement with the results of TCAD. As a results of our analysis using this analytical threshold voltage model, the change in the threshold voltage with respect to the change in the ferroelectric thickness showed that the threshold voltage increased with the increase of the absolute value of charges in the employed ferroelectric. This suggests that it is possible to obtain an optimum ferroelectric thickness at which the threshold voltage shift becomes 0 V by the voltage across the ferroelectric even when the channel length is reduced. It was also found that the ferroelectric thickness increased as the silicon thickness increased when the channel length was less than 30 nm, but the ferroelectric thickness decreased as the silicon thickness increased when the channel length was 30 nm or more in order to satisfy ΔV_th=0.

Hf_0.5Zr_0.5O₂ 강유전체 박막의 다양한 분극 스위칭 모델에 의한 동역학 분석

안승언,Ahn, Seung-Eon 한국재료학회 2020 한국재료학회지 Vol.30 No.2

Recent discoveries of ferroelectric properties in ultrathin doped hafnium oxide (HfO₂) have led to the expectation that HfO₂ could overcome the shortcomings of perovskite materials and be applied to electron devices such as Fe-Random access memory (RAM), ferroelectric tunnel junction (FTJ) and negative capacitance field effect transistor (NC-FET) device. As research on hafnium oxide ferroelectrics accelerates, several models to analyze the polarization switching characteristics of hafnium oxide ferroelectrics have been proposed from the domain or energy point of view. However, there is still a lack of in-depth consideration of models that can fully express the polarization switching properties of ferroelectrics. In this paper, a Zr-doped HfO₂ thin film based metal-ferroelectric-metal (MFM) capacitor was implemented and the polarization switching dynamics, along with the ferroelectric characteristics, of the device were analyzed. In addition, a study was conducted to propose an applicable model of HfO₂-based MFM capacitors by applying various ferroelectric switching characteristics models.

Thin reduced graphene oxide interlayer with a conjugated block copolymer for high performance non-volatile ferroelectric polymer memory

Velusamy, D.B.,Kim, R.H.,Takaishi, K.,Muto, T.,Hashizume, D.,Lee, S.,Uchiyama, M.,Aoyama, T.,Ribierre, J.C.,Park, C. Elsevier Science 2014 Organic electronics Vol.15 No.11

Polymer ferroelectric-gate field effect transistors (Fe-FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next-generation non-volatile memory. For minimizing gate leakage current of a device which arises from electrically defective ferroelectric polymer layer in particular at low operation voltage, the materials design of interlayers between the ferroelectric insulator and gate electrode is essential. Here, we introduce a new solution-processed interlayer of conductive reduced graphene oxides (rGOs) modified with a conjugated block copolymer, poly(styrene-block-paraphenylene) (PS-b-PPP). A FeFET with a solution-processed p-type oligomeric semiconducting channel and ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) insulator exhibited characteristic source-drain current hysteresis arising from ferroelectric polarization switching of a PVDF-TrFE insulator. Our PS-b-PPP modified rGOs (PMrGOs) with conductive moieties embedded in insulating polymer matrix not only significantly reduced the gate leakage current but also efficiently lowered operation voltage of the device. In consequence, the device showed large memory gate voltage window and high ON/OFF source-drain current ratio with excellent data retention and read/write cycle endurance. Furthermore, our PMrGOs interlayers were successfully employed to FeFETs fabricated on mechanically flexible substrates with promising non-volatile memory performance under repetitive bending deformation.

High Performance Multi‐Level Non‐Volatile Polymer Memory with Solution‐Blended Ferroelectric Polymer/High‐<i>k</i> Insulators for Low Voltage Operation

Hwang, Sun Kak,Bae, Insung,Cho, Suk Man,Kim, Richard Hahnkee,Jung, Hee Joon,Park, Cheolmin WILEY‐VCH Verlag 2013 Advanced functional materials Vol.23 No.44

<P><B>Abstract</B></P><P>Polymer ferroelectric‐gate field effect transistors (Fe‐FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next‐generation non‐volatile memory. Furthermore, polymer Fe‐FETs have been recently of interest owing to their capability of storing data in more than 2 states in a single device, that is, they have multi‐level cell (MLC) operation potential for high density data storage. However, among a variety of technological issues of MLC polymer Fe‐FETs, the requirement of high voltage for cell operation is one of the most urgent problems. Here, a low voltage operating MLC polymer Fe‐FET memory with a high dielectric constant (<I>k</I>) ferroelectric polymer insulator is presented. Effective enhancement of capacitance of the ferroelectric gate insulator layer is achieved by a simple binary solution‐blend of a ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) (<I>k</I> ≈ 8) with a relaxer high‐<I>k</I> poly(vinylidene‐fluoride–trifluoroethylene–chlorotrifluoroethylene) (PVDF‐TrFE‐CTFE) (<I>k</I> ≈ 18). At optimized conditions, a ferroelectric insulator with a PVDF‐TrFE/PVDF‐TrFE‐CTFE (10/5) blend composition enables the discrete six‐level multi‐state operation of a MLC Fe‐FET at a gate voltage sweep of ±18 V with excellent data retention and endurance of each state of more than 10<SUP>4</SUP> s and 120 cycles, respectively.</P>

Mesoscopic-scale grain formation in HfO2-based ferroelectric thin films and its impact on electrical characteristics

Kobayashi Masaharu,Wu Jixuan,Sawabe Yoshiki,Takuya Saraya,Hiramoto Toshiro 나노기술연구협의회 2022 Nano Convergence Vol.9 No.50

Ferroelectric memory devices are expected for low-power and high-speed memory applications. ­HfO 2 -based fer- roelectric is attracting attention for its CMOS-compatibility and high scalability. Mesoscopic-scale grains, of which size is almost comparable to device size, are formed in ­HfO 2 -based ferroelectric poly-crystalline thin films, which largely influences electrical characteristics in memory devices. It is important to study the impact of mesoscopic-scale grain formation on the electrical characteristics. In this work, first, we have studied the thickness dependence of the polarization switching kinetics in ­HfO 2 -based ferroelectric. While static low-frequency polarization is comparable for different thickness, dynamic polarization switching speed is slower in thin ­Hf 0.5 Zr 0.5 O 2 (HZO) capacitors. Based on the analysis using the NLS model and physical characterization, thinner HZO contains smaller grains with orientation non-uniformity and more grain boundaries than thicker HZO, which can impede macroscopic polarization switching. We have also theoretically and experimentally studied the polar-axis alignment of a ­HfO 2 -based ferroelectric thin film. While in-plane polar orientation is stable in as-grown HZO, out-of-plane polarization can be dominant by applying electric field, which indicates the transition from in-plane polar to out-of-plane polar orientation in the ferroelectric phase grains. This is confirmed by calculating kinetic pathway using ab-initio calculation.

Nanostructured Ferroelectrics: Fabrication and Structure–Property Relations

Han, Hee,Kim, Yunseok,Alexe, Marin,Hesse, Dietrich,Lee, Woo WILEY‐VCH Verlag 2011 Advanced Materials Vol. No.

<P><B>Abstract</B></P><P>With the continued demand for ultrahigh density ferroelectric data storage applications, it is becoming increasingly important to scale the dimension of ferroelectrics down to the nanometer‐scale region and to thoroughly understand the effects of miniaturization on the materials properties. Upon reduction of the physical dimension of the material, the change in physical properties associated with size reduction becomes extremely difficult to characterize and to understand because of a complicated interplay between structures, surface properties, strain effects from substrates, domain nucleation, and wall motions. In this Review, the recent progress in fabrication and structure‐property relations of nanostructured ferroelectric oxides is summarized. Various fabrication approaches are reviewed, with special emphasis on a newly developed stencil‐based method for fabricating ferroelectric nanocapacitors, and advantages and limitations of the processes are discussed. Stress‐induced evolutions of domain structures upon reduction of the dimension of the material and their implications on the electrical properties are discussed in detail. Distinct domain nucleation, growth, and propagation behaviors in nanometer‐scale ferroelectric capacitors are discussed and compared to those of micrometer‐scale counterparts. The structural effect of ferroelectric nanocapacitors on the domain switching behavior and cross‐talk between neighboring capacitors under external electric field is reviewed.</P>

플루오라이트 구조 강유전체 박막의 분극 반전 동역학 리뷰

김세현(Se Hyun Kim),박근형(Keun Hyeong Park),이은빈(Eun Been Lee),유근택(Geun Taek Yu),이동현(Dong Hyun Lee),양건(Kun Yang),박주용(Ju Yong Park),박민혁(Min Hyuk Park) 한국표면공학회 2020 한국표면공학회지 Vol.53 No.6

Since the original report on ferroelectricity in Si-doped HfO₂ in 2011, fluorite-structured ferroelectrics have attracted increasing interest due to their scalability, established deposition techniques including atomic layer deposition, and compatibility with the complementary-metal-oxide-semiconductor technology. Especially, the emerging fluorite-structured ferroelectrics are considered promising for the next-generation semiconductor devices such as storage class memories, memory-logic hybrid devices, and neuromorphic computing devices. For achieving the practical semiconductor devices, understanding polarization switching kinetics in fluorite-structured ferroelectrics is an urgent task. To understand the polarization switching kinetics and domain dynamics in this emerging ferroelectric materials, various classical models such as Kolmogorov-Avrami-Ishibashi model, nucleation limited switching model, inhomogeneous field mechanism model, and Du-Chen model have been applied to the fluorite-structured ferroelectrics. However, the polarization switching kinetics of fluorite-structured ferroelectrics are reported to be strongly affected by various nonideal factors such as nanoscale polymorphism, strong effect of defects such as oxygen vacancies and residual impurities, and polycrystallinity with a weak texture. Moreover, some important parameters for polarization switching kinetics and domain dynamics including activation field, domain wall velocity, and switching time distribution have been reported quantitatively different from conventional ferroelectrics such as perovskite-structured ferroelectrics. In this focused review, therefore, the polarization switching kinetics of fluorite-structured ferroelectrics are comprehensively reviewed based on the available literature.

Current Status and Prospects of FET-type Ferroelectric Memories

Ishiwara, Hiroshi The Institute of Electronics and Information Engin 2001 Journal of semiconductor technology and science Vol.1 No.1

Current status and prospects of FET-type FeRAMs (ferroelectric random access memories) are reviewed. First, it is described that the most important issue for realizing FET-type FeRAMs is to improve the data retention characteristics of ferroelectric-gate FETs. Then, necessary conditions to prolong the retention time are discussed from viewpoints of materials, device structure, and circuit configuration. Finally, recent experimental results related to the FET-type memories are introduced, which include optimization of a buffer layer that is inserted between the ferroelectric film and a Si substrate, development of a new ferroelectric film with a small remnant polarization value, proposal and fabrication of a 1T2C-type memory cell with good retention characteristics, and so on.

Effect of preparation of organic ferroelectric P(VDF-TrFE) nanostructure on the improvement of tennis performance

Qingyu Wang Techno-Press 2023 Advances in nano research Vol.14 No.4

Organic ferroelectric material found vast application in a verity of engineering and health technology fields. In the present study, we investigated the application of the deformable organic ferroelectric in motion measurement and improving performance in tennis players. Flexible ferroelectric material P(VDF-TrFE) could be used in wearable motion sensors in tennis player transferring velocity and acceleration data to collecting devises for analyzing the best pose and movements in tennis players to achieve best performances in terms of hitting ball and movement across the tennis court. In doing so, ferroelectric-based wearable sensors are used in four different locations on the player body to analyze the movement and also a sensor on the tennis ball to record the velocity and acceleration. In addition, poses of tennis players were analyzed to find out the best pose to achieve best acceleration and movement. The results indicated that organic ferroelectric-based sensors could be used effectively in sensing motion of tennis player which could be utilized in the optimization of posing and ball hitting in the real games.