Scaling behavior of ferroelectric FET with reduction in number of domains in ferroelectric layer

With the gate-length scaling, the number of domains in FeFET is reduced to a few or a single domain. In this paper, we investigate the effect of multi-domains versus few/single-domain behavior in FeFET. The abrupt polarization switching behavior of a single-domain is obtained by modifying the Preisach model in which the difference between saturation and remnant polarization (PsPr) is reduced. We show that for the same program/erase voltage, a two-times higher memory window can be achieved with single/few-domains FeFET than the multi-domain FeFET. Further, at fixed program/erase voltage, the scaling behavior shows improved variability due to increased polarization-induced vertical field with single-domain FeFET. We present an optimized device with a single-domain FeFET having a low operating voltage of ±2.4 V but with the same device performance that can be achieved for multi-domain FeFET having a higher operating voltage of ±5 V, which is highly promising for low power applications.

Quantitative investigation of polarization-dependent photocurrent in ferroelectric thin films

Ferroelectric thin films are investigated for their potential in photovoltaic (PV) applications, owing to their high open-circuit voltage and switchable photovoltaic effect. The direction of the ferroelectric polarization can control the sign of the photocurrent through the ferroelectric layer, theoretically allowing for 100 percent switchability of the photocurrent with the polarization, which is particularly interesting for photo-ferroelectric memories. However, the quantitative relationship between photocurrent and polarization remains little studied. In this work, a careful investigation of the polarization-dependent photocurrent of epitaxial Pb(Zr,Ti)O3 thin films has been carried out, and has provided a quantitative determination of the unswitchable part of ferroelectric polarization. These results represent a systematic approach to study and optimize the switchability of photocurrent, and more broadly to get important insights on the ferroelectric behavior in all types of ferroelectric layers in which pinned polarization is difficult to investigate.

Self-selective ferroelectric memory realized with semimetalic graphene channel

A new concept of read-out method for ferroelectric random-access memory (FeRAM) using a graphene layer as the channel material of bottom-gated field effect transistor structure is demonstrated experimentally. The transconductance of the graphene channel is found to change its sign depending on the direction of spontaneous polarization (SP) in the underlying ferroelectric layer. This indicates that the memory state of FeRAM, specified by the SP direction of the ferroelectric layer, can be sensed unambiguously with transconductance measurements. With the proposed read-out method, it is possible to construct an array of ferroelectric memory cells in the form of a cross-point structure where the transconductance of a crossing cell can be measured selectively without any additional selector. This type of FeRAM can be a plausible solution for fabricating high speed, ultra-low power, long lifetime, and high density 3D stackable non-volatile memory.

Comprehensive investigation on RF/analog parameters in ferroelectric tunnel FET

In this paper, the effect of ferroelectric layer thickness (tFE), coercive field (Ec), remnant polarization (Pr), and saturation polarization (Ps) on transfer characteristic is highlighted for a Ferroelectric Tunnel FET (Fe-TFET) through a commercial TCAD simulator. Further, we have reported the RF/analog parameters like transconductance (gm), output conductance (gd), gain (gm/gd), gate capacitance (Cgg), and cut off frequency (ft) for wide range of FE parameters in Fe-TFET. Improved RF/analog performance and transfer characteristic are obtained for low value of tFE, Pr, Ec, whereas, these behavior is degraded at high value of Ps.

Simulation-based Analysis of Ultra Thin-body Double Gate Ferroelectric TFET for an Enhanced Electric Performance

The Ultrathin body double gate FE layer TFET(UTB-DG-FE-TFET) is proposed and investigated in this work. Electrical performance parameters such as surface potential ψ(x), electrical field, drain current, sub-threshold swing, threshold voltage, and I on /I off ratio are further analyzed using simulation-based analysis. Integration of Si: HFO 2 ferroelectric layer on top and bottom surfaces make the structure that provides negative capacitance, higher on current, enormous surface potential, peak electric field, and improvement in SS with degradation in off Current. The suggested design is evaluated in comparison with FE-TFET and standard TFET devices. Finally, the impact of device geometry variants like ferroelectric layer thickness (t fe ), intrinsic channel thickness t si , interfacial layer types, interfacial layer thickness (t ox ) and channel length L c on transfer characteristics are investigated through 2D TCAD Sentaurus Simulator for a clear validation of its optimization. The recommended work demonstrates that it is a suitable device enabling superior performance and helpful in ultra-low-power applications.

Enhancement of Magnetoelectric Effect in Compositionally Graded Ferroelectric/Ferromagnetic Pb(1−x)SrxTiO3/CoFe2O4 Nanocomposites

In this study, phase-field model is developed for ferroelectric/ferromagnetic nanocomposites, in which ferroelectric composition is spatially varied along the thickness of ferroelectric layers. The developed phase field model is applied to investigate the effect of composition gradient on magnetoelectric response of the multilayer nanocomposite. Stripe domain structures are observed in both ferroelectric and ferromagnetic layers, however the sizes of magnetic domains are larger than that of polarization ones. Particularly, the size of polarization domains and geometry of domain walls are altered according to the gradient of ferroelectric composition. The obtained results suggest that the larger the composition gradient is, the higher the magnetoelectric effect becomes. The enhancement of magnetoelectric effect is attributed to the concentration of energy in ferroelectric layer, which originates from the spatial variation of ferroelectric composition.

Suppression of Acoustic Resonances in BST-Based Bulk-Ceramic Varactors by Addition of Magnesium Borate

This work presents a method for reducing acoustic resonances in ferroelectric barium strontium titanate (BST)-based bulk ceramic varactors, which are capable of operation in high-power matching circuits. Two versions of parallel-plate varactors are manufactured here: one with pure BST and one with 10 vol-% magnesium borate, Mg3B2O6 (MBO). Each varactor includes a 0.85-mm-thick ferroelectric layer. Acoustic resonances that are present in the pure BST varactor are strongly suppressed in the BST-MBO varactor and, hence, the Q-factor is increased over a wide frequency range by the addition of small amounts of a low-dielectric-constant (LDK) MBO. Although the tunability is reduced due to the presence of non-tunable MBO, the increased Q-factor extends the varactor’s availability for low-loss and high-power applications.

Impact of Rapid-Thermal-Annealing Temperature on the Polarization Characteristics of a PZT-Based Ferroelectric Capacitor

A metal-ferroelectric-metal (MFM) capacitor was fabricated to investigate the effect of the rate-of-change of temperature in the rapid thermal annealing (RTA) process on the physical properties of the MFM capacitor’s ferroelectric layer [lead zirconate oxide (PZT)]. Remnant polarization (2 × Pr) is measured and monitored while performing the RTA process at 500 °C–700 °C. It turned out that, for a given target/final temperature in the RTA process, 2Pr of the ferroelectric layer decreases with a higher rate-of-change of temperature. This can provide a way to adjust the properties of the PZT layer, depending on the RTA process condition (i.e., using various rate-of-changes of temperature) for a given final/target temperature.