Ferroelectric Transistor Memory Research Articles

Impact of annealing temperature on the ferroelectric properties of W/Hf0.5Zr0.5O2/W capacitor

Crystallization annealing is a crucial process for the formation of the ferroelectric phase in HfO2-based ferroelectric thin films. Here, we systematically investigate the impact of the annealing process, with temperature varied from 350 °C to 550 °C, on the electricity, ferroelectricity and reliability of a Hf0.5Zr0.5O2 (HZO; 7.5 nm) film capacitor. It was found that HZO film annealed at a low temperature of 400 °C can effectively suppress the formation of the monoclinic phase and reduce the leakage current. HZO film annealed at 400 °C also exhibits better ferroelectric properties than those annealed at 350 °C and 550 °C. Specifically, the 400 °C-annealed HZO film shows an outstanding 2P r value of 54.6 μC⋅cm−2 at ± 3.0 MV⋅cm−1, which is relatively high compared with previously reported values for HZO film under the same electric field and annealing temperature. When the applied electric field increases to ± 5.0 MV⋅cm−1, the 2P r value can reach a maximum of 69.6 μC⋅cm−2. In addition, the HZO films annealed at 400 °C and 550 °C can endure up to bout 2.3 × 108 cycles under a cycling field of 2.0 MV⋅cm−1 before the occurrence of breakdown. In the 400 °C-annealed HZO film, 72.1% of the initial polarization is maintained while only 44.9% is maintained in the 550 °C-annealed HZO film. Our work demonstrates that HZO film with a low crystallization temperature (400 °C) has quite a high ferroelectric polarization, which is of significant importance in applications in ferroelectric memory and negative capacitance transistors.

Novel Fluorite-Structured Materials for Solid-State Refrigeration.

Refrigeration based on the electrocaloric effect can offer many advantages over conventional cooling technologies in terms of efficiency, size, weight, and power source. The discovery of ferroelectric and antiferroelectric properties in fluorite-based materials in 2011 has led to diverse applications related to memory (e.g., ferroelectric tunnel junctions, nonvolatile memory, and field-effect transistors) and energy fields (e.g., energy storage and harvesting, electrocaloric refrigeration, and infrared detection). Fluorite-based materials exhibit several properties not shared by most conventional materials (such as in terms of compatibility with complementary metal-oxide semiconductors and 3D nanostructures, deposition thickness at the nanometer scale, and simple composition). Here, the electrocaloric refrigeration properties of fluorite-based ferroelectric/antiferroelectric materials are reviewed by focusing on the advantages of ZrO2 - and HfO2 -based materials (e.g., relative to conventional perovskite- and polymer-based counterparts). Finally, the recent progress made in this research field are also discussed along with its future perspectives.

Complementary of Ferroelectric and Floating Gate Structure for High Performance Organic Nonvolatile Memory

AbstractOrganic thin film transistor (OTFT) based nonvolatile memory has made significant progress due to its biocompatibility, flexibility, and low cost, in which ferroelectric transistor memory and floating gate transistor memory play the main roles in organic nonvolatile transistor memory. Here, a novel layered hybrid structure OTFT nonvolatile memory is invented by combining ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) P(VDF‐TrFE) with a floating gate layer utilizing CdSe/ZnS quantum dots (QDs), which integrates the advantages of ferroelectric memory and floating gate memory. The core–shell structured CdSe/Zns QDs are acted as robust charge trapping centers due to their band structure similar to a quantum well, preventing the back diffuse of trapped charges, while P(VDF‐TrFE) provides additional polarized electric field to modulate the capture of charge. The resultant devices exhibit high on‐state current (≈10−5 A), low off‐state current (≈10−10 A), excellent switch ratio (≈105), and retention characteristic (>104 s). Furthermore, a superior memory window, more than 85.6% of scanning voltage range, higher than most reported organic transistor memories, is achieved, which endows the device wide operating condition and significant discrimination between on and off state. The fine‐structured OTFT memory opens up a unique path for desirable memory to meet the growing demand of microelectronic industry.

Solution‐Processed Dual Gate Ferroelectric–Ferroelectric Organic Polymer Field‐Effect Transistor for the Multibit Nonvolatile Memory

AbstractThe stable multibit storage operation of solution‐processed organic nonvolatile memories (ONVMs) based on ferroelectric field‐effect transistors (FeFETs) for high density data storage devices are demonstrated. The proposed multibit ONVM structure consists of a p‐type polymer semiconductor sandwiched between poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] layers serving as ferroelectric gate insulators to form a dual gate ferroelectric–ferroelectric memory transistor (DG Fe‐FeMT). With the extra memory space created by the spatially separated ferroelectrics, a 2‐bit memory representation (“11”, “10”, “01” and “00”) with clear memory margins is achieved due to the bistability of each P(VDF‐TrFE) and the high performance of the polymer semiconductor. The distinct four‐level reading of memory output currents (IM,OUTs) results from the independent programming voltages of the dual gates. An excellent distinct six‐levelIM,OUTsare also achieved in DG Fe‐FeMT using the intermediate programming voltages. Finally, the possibility of 3−bit, or 8 memory states, are demonstrated by optimizing the bistability and intermediate polarization states of the ferroelectrics without increasing the device area horizontally. The DG Fe‐FeMT has a great potential for cost−effective flexible nonvolatile multibit data storage devices due to its solution‐process and low annealing temperatures.

Ferroelectric HfO2 Memory Transistors With High-κ Interfacial Layer and Write Endurance Exceeding 1010 Cycles

We demonstrate ferroelectric (FE) memory transistors on a crystalline silicon channel with endurance exceeding 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> cycles. The ferroelectric transistors (FeFETs) incorporate a high- κ interfacial layer (IL) of thermally grown silicon nitride (SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) and a thin 4.5 nm layer of Zr-doped FE-HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (HZO) on a ~30 nm silicon on insulator (SOI) channel. The device shows a ~1V memory window (MW) in a DC sweep of just ± 2.5V, and can be programmed and erased with voltage pulses of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> G</sub> = ± 3V at a pulse width of 250 ns. The device also shows very good retention behavior. These results indicate that appropriate engineering of the IL layer could substantially improve FeFET device performance and reliability.

Enhancement of the Retention Characteristics in Solution-Processed Ferroelectric Memory Transistor with Dual-Gate Structure.

We demonstrated the enhancement of the retention characteristics in solution-processed ferroelectric memory transistors. For enhanced retention characteristics, solution-processed Indium Gallium Zinc Oxide (InGaZnO) semiconductor is used as an active layer in a dual-gate structure to achieve high memory on-current and low memory off-current respectively. In our dual-gate oxide ferroelectric thin-film transistor (DG Ox-FeTFT), while conventional TFT characteristic is observed during bottom-gate sweeping, large hysteresis is exhibited during top-gate sweeping with high memory on-current due to the high mobility of the InGaZnO. The voltage applied to the counter bottom-gate electrode causes variations in the turn-on voltage position, which controlled the memory on- and off-current in retention characteristics. Specifically, due to the full depletion of semiconductor by the high negative counter gate bias, the memory off-current in reading operation is dramatically reduced by 10⁴. The application of a high negative counter field to the dual-gate solution-processed ferroelectric memory gives a high memory on- and off-current ratio useful for the production of high performance multi-bit memory devices.

Computationally efficient compact model for ferroelectric field-effect transistors to simulate the online training of neural networks

In this paper, a compact drain current formulation that is simple and adequately computationally efficient for the simulation of neural network online training was developed for the ferroelectric memory transistor. Tri-gate ferroelectric field-effect transistors (FETs) with Hf0.5Zr0.5O2 gate insulators were fabricated with a gate-first high-k metal gate CMOS process. Ferroelectric switching was confirmed with double sweep and pulse programming and erasure measurements. Novel characterization scheme for drain current was proposed with minimal alteration of ferroelectric state in subthreshold for accurate threshold voltage measurements. The resultant threshold voltage exhibited highly linear and symmetric across multilevel states. The proposed compact formulation accurately captured the FET gate-bias dependence by considering the effects of series resistance, Coulomb scattering, and vertical field dependent mobility degradation.

Complementary Type Ferroelectric Memory Transistor Circuits with P‐ and N‐Channel MoTe2

AbstractFerroelectric nonvolatile memory (FeNVM) field effect transistors (FETs) are reported using p‐channel MoTe2 and P(VDF‐TrFE) ferroelectric polymer, and furthermore a complementary type memory cell is demonstrated coupling p‐ and n‐channel MoTe2 FETs. A top‐gate p‐FET with P(VDF‐TrFE) and a bottom‐gate n‐FET with Al2O3 dielectric are integrated as one cell. Such a complementary type cell is more desirable research path in respect of power consumption but rare to find in 2D‐based memory reports. Among many 2D semiconductors MoTe2 is selected, because p‐type MoTe2‐based FeNVM is not reported yet, and also because it is relatively easy to obtain both p‐ and n‐channel from the homogeneous MoTe2. The integrated device also operates as a complementary metal oxide semiconductor inverter in a small voltage range from 0 to ≈2.5 V, but primarily works as a FeNVM circuit when p‐channel with top P(VDF‐TrFE) is biased with high voltages over the coercive electric field (Ec) of the polymer. The bottom gate n‐channel transistor operates as a switching device in the FeNVM cell, allowing voltage output signals during device operations. It is concluded that the complementary type FeNVM cell is practical and novel enough to report as a first time demonstration based on 2D MoTe2.

Self-polarized Poly(vinylidene fluoride) Ultrathin Film and Its Piezo/Ferroelectric Properties.

Organic nonvolatile memory with ultralow power consumption is a critical research demand for next-generation memory applications. However, obtaining a large-area, highly oriented ferroelectric ultrathin film with low leakage current and stable ferroelectric switching remains a challenge for achieving low operation voltage in ferroelectric memory transistors. Here, an ideal ferroelectric neat PVDF ultrathin film with a high degree of orientation is fabricated by a melt-draw technique without post-thermal treatment and assisted stabilization process. The PVDF ultrathin film is self-polarized with predominantly vertical orientation of dipole moments, exhibiting a d33 of 25 pm V-1 and the ultralow coercive voltage of approximately 3 V characterized by piezoresponse force microscopy. A remnant polarization of 6.3 μC cm-2 is identified based on a PVDF capacitor with an active layer formed by six layers of melt-drawn thin films. By employing a single-layer melt-drawn PVDF ultrathin film as an insulation layer, a bottom-gate-top-contact ferroelectric field-effect transistor is fabricated with a very low operation voltage of 5 V. It exhibits a memory window with an on/off current ratio of 103 at zero gate bias and threshold voltage shift of around 2 V.

All‐Solid‐State Organic Schmitt Trigger Implemented by Twin Two‐in‐One Ferroelectric Memory Transistors

AbstractAlthough there have been many attempts to replace conventional inorganic electronics with organic materials that can be mass produced at low cost, few organic electronic filters to increase immunity to electrical noise have been reported thus far. Conventional Schmitt triggers or their inverters are used in many electronic circuits as versatile electronic noise filters. However, it is challenging to manufacture organic electronic systems with complex circuitry. In this study, a simple, all‐solid‐state organic Schmitt trigger consisting of twin two‐in‐one organic ferroelectric memory transistors with the same chemical compositions and device dimensions but different threshold voltages is introduced. Threshold voltages and hysteresis in the two‐in‐one devices can be controlled by polarization switching as demonstrated in a previous study. Hysteresis of a ferroelectric p‐type depletion load inverter can be achieved using twin two‐in‐one devices when the sweep voltage is higher than the critical gate voltages. This facilitates inverter characteristics at two different threshold voltages, and realizing a Schmitt trigger. Finally, based on simulation program with integrated circuit emphasis (SPICE) simulation, guidelines are proposed on how to design organic Schmitt triggers with p‐ or n‐type materials and ferroelectric or charge‐trapping mechanisms to achieve inverting or non‐inverting characteristics.

Carbon nanotube ferroelectric random access memory cell based on omega-shaped ferroelectric gate

This paper presents a flexible ferroelectric random access memory (FeRAM) cell with a one-transistor-one-transistor structure. The FeRAM cell was composed of a control transistor (CT) and an omega-shaped ferroelectric memory transistor (MT). An inkjet-printed single-walled carbon nanotube (SWCNT) were utilized as a semiconducting channel layers of both transistors. An omega-shaped ferroelectric gate was formed through inkjet-printing of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) onto the SWCNT channel of the MT. The gate electrode of the CT was electrically connected to the drain electrode of the MT, while the gate electrode of the MT was connected to the source electrode of the CT. The 1T1T architecture enabled the separation of the writing and reading operations, which afforded nondestructive readout capability. The desired multi-level conductance states could be deterministically controlled by tuning the dipole polarization in the ferroelectric P(VDF-TrFE) layer of the MT. The resulting FeRAM cell showed excellent device performances such as five-level data storage, a high programming/erasing current ratio (>105), a retention time (>104 s), and operational stability (>1000 cycles). The 1T1T FeRAM cell fabricated by inkjet printing technique opens up new opportunities for realizing future large-area flexible memory cells.

Excellent Ferroelectric Properties of Hf0.5Zr0.5O2 Thin Films Induced by Al2O3 Dielectric Layer

The ferroelectricity of Hf0.5Zr0.5O2 (HZO) thin films has been usually reported to be induced by metallic capping layer. In this work, we successfully obtained ferroelectricity of HZO thin films induced by ultrathin insulating Al2O3 capping layers. The ferroelectric properties of HZO thin films induced by Al2O3 capping layers with different thickness have been investigated. It was found that the Al2O3(2 nm)/HZO (20 nm) stack shows excellent ferroelectric properties. The Au/Al2O3(2 nm)/HZO (20 nm)/TiN capacitor exhibits a very low leakage current of $\sim {4.2}\times {10}^{\text {-9}}$ A at 4 V and a maximum $2{P}_{r}\approx 32.3~\mu \text{C}$ /cm2 at sweeping voltages between ±8 V. In addition, the capacitor also shows excellent endurance properties up to 108 cycles. Our work demonstrated that dielectric films like Al2O3 can be adopted to be used as capping layer to generate excellent ferroelectric properties of HfO2-based thin films, which will contribute to their future applications in ferroelectric memory and negative capacitance transistors.

Two-in-One Device with Versatile Compatible Electrical Switching or Data Storage Functions Controlled by the Ferroelectricity of P(VDF-TrFE) via Photocrosslinking

Organic electronics demand new platforms that can make integrated circuits and undergo mass production while maintaining diverse functions with high performance. The field-effect transistor has great potential to be a multifunctional device capable of sensing, data processing, data storage, and display. Currently, transistor-based devices cannot be considered intrinsic multifunctional devices because all installed functions are mutually coupled. Such incompatibilities are a crucial barrier to developing an all-in-one multifunctional device capable of driving each function individually. In this study, we focus on the decoupling of electric switching and data storage functions in an organic ferroelectric memory transistor. To overcome the incompatibility of each function, the high permittivity needed for electrical switching and the ferroelectricity needed for data storage become compatible by restricting the motion of poly(vinylidene fluoride-trifluoroethylene) via photocrosslinking with bis-perfluorobenzoazide. The two-in-one device consisting of a photocrosslinked ferroelectric layer exhibits reversible and individual dual-functional operation as a typical transistor with nonvolatile memory. Moreover, a p-MOS depletion load inverter composed of the two transistors with different threshold voltages is also demonstrated by simply changing only one of the threshold voltages by polarization switching. We believe that the two-in-one device will be considered a potential component of integrated organic logic circuits, including memory, in the future.

Band alignments at Hf1-Zr O2/Si and Hf0.52Zr0.48O2/Si0.55Ge0.45 interfaces

Abstract Hf1-xZrxO2 films have attracted significant attention for applications in ferroelectric memory and negative capacitance transistors due to their ferroelectric properties and high compatibility to CMOS integration. X-ray photoelectron spectroscopy (XPS) was utilized to characterize the energy band alignments of Hf1-xZrxO2/Si and bandgaps of Hf1-xZrxO2 with different Zr compositions. Results show with the increment of Zr composition in Hf1-xZrxO2 from 0 to 1, the valence band offset ΔEv for Hf1-xZrxO2/Si interfaces increases from 2.09 to 2.94 eV, while the conduction band offset ΔEc decreases from 2.37 to 1.06 eV. This is resulted from the increasing Zr composition leading to a decrement of bandgap and electron affinity in Hf1-xZrxO2. Both ΔEv and ΔEc are all above 1 eV, which is large enough to block electrons and holes for carrier transport in channel regions for the Hf1-xZrxO2 based transistors. The band alignment for Hf0.52Zr0.48O2/Si0.55Ge0.45 was also investigated exhibiting a much larger ΔEv and a slightly lower ΔEc as compared to Hf0.52Zr0.48O2/Si.

Direct visualization of polarization reversal of organic ferroelectric memory transistor by using charge modulated reflectance imaging

By using the charge modulated reflectance (CMR) imaging technique, charge distribution in the pentacene organic field-effect transistor (OFET) with a ferroelectric gate insulator [P(VDF-TrFE)] was investigated in terms of polarization reversal of the P(VDF-TrFE) layer. We studied the polarization reversal process and the carrier spreading process in the OFET channel. The I-V measurement showed a hysteresis behavior caused by the spontaneous polarization of P(VDF-TrFE), but the hysteresis I-V curve changes depending on the applied drain bias, possibly due to the gradual shift of the polarization reversal position in the OFET channel. CMR imaging visualized the gradual shift of the polarization reversal position and showed that the electrostatic field formed by the polarization of P(VDF-TrFE) contributes to hole and electron injection into the pentacene layer and the carrier distribution is significantly dependent on the direction of the polarization. The polarization reversal position in the channel region is governed by the electrostatic potential, and it happens where the potential reaches the coercive voltage of P(VDF-TrFE). The transmission line model developed on the basis of the Maxwell-Wagner effect element analysis well accounts for this polarization reversal process in the OFET channel.

Enhancement of the Electrical Performance of the Organic Ferroelectric Memory Transistor by Reducing the Surface Roughness of the Polymer Insulator with a Homo-Bilayer PVDF-TrFE

Enhancement of the Electrical Performance of the Organic Ferroelectric Memory Transistor by Reducing the Surface Roughness of the Polymer Insulator with a Homo-Bilayer PVDF-TrFE

Organic Ferroelectric-Based 1T1T Random Access Memory Cell Employing a Common Dielectric Layer Overcoming the Half-Selection Problem.

Organic electronics based on poly(vinylidenefluoride/trifluoroethylene) (P(VDF-TrFE)) dielectric is facing great challenges in flexible circuits. As one indispensable part of integrated circuits, there is an urgent demand for low-cost and easy-fabrication nonvolatile memory devices. A breakthrough is made on a novel ferroelectric random access memory cell (1T1T FeRAM cell) consisting of one selection transistor and one ferroelectric memory transistor in order to overcome the half-selection problem. Unlike complicated manufacturing using multiple dielectrics, this system simplifies 1T1T FeRAM cell fabrication using one common dielectric. To achieve this goal, a strategy for semiconductor/insulator (S/I) interface modulation is put forward and applied to nonhysteretic selection transistors with high performances for driving or addressing purposes. As a result, high hole mobility of 3.81 cm2 V-1 s-1 (average) for 2,6-diphenylanthracene (DPA) and electron mobility of 0.124 cm2 V-1 s-1 (average) for N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2 ) are obtained in selection transistors. In this work, we demonstrate this technology's potential for organic ferroelectric-based pixelated memory module fabrication.

Roughness Reduction of PVDF-TrFE Insulator by Reverse Transfer Printing for Enhanced Performance of Ferroelectric Organic Memory Transistors

Roughness Reduction of PVDF-TrFE Insulator by Reverse Transfer Printing for Enhanced Performance of Ferroelectric Organic Memory Transistors

Modeling and simulation of low power ferroelectric non-volatile memory tunnel field effect transistors using silicon-doped hafnium oxide as gate dielectric

The implementation and operation of the nonvolatile ferroelectric memory (NVM) tunnel field effect transistors with silicon-doped HfO2 is proposed and theoretically examined for the first time, showing that ferroelectric nonvolatile tunnel field effect transistor (Fe-TFET) can operate as ultra-low power nonvolatile memory even in aggressively scaled dimensions. A Fe-TFET analytical model is derived by combining the pseudo 2-D Poisson equation and Maxwell’s equation. The model describes the Fe-TFET behavior when a time-dependent voltage is applied to the device with hysteretic output characteristic due to the ferroelectric’s dipole switching. The theoretical results provide unique insights into how device geometry and ferroelectric properties affect the Fe-TFET transfer characteristic. The recently explored ferroelectric, silicon-doped HfO2 is employed as the gate ferroelectric. With the ability to engineer ferroelectricity in HfO2 thin films, a high-K dielectric well established in memory devices, the silicon-doped HfO2 opens a new route for improved manufacturability and scalability of future 1-T ferroelectric memories. In the current research, a Si:HfO2 based Fe-TFET with large memory window and low power dissipation is designed and simulated. Utilizing our presented model, the device characteristics of a Fe-TFET that takes full benefits from Si:HfO2 is compared with the same devices using well-known perovskite ferroelectrics. Finally, the Fe-TFET is compared with a conventional ferroelectric memory transistor highlighting the advantages of using tunneling memory devices.

Non-volatile organic ferroelectric memory transistors fabricated using rigid polyimide islands on an elastomer substrate

The authors fabricated stretchable organic ferroelectric memory transistors (OFMTs) on a polydimethylsiloxane substrate using rigid polyimide island structures.