Nonvolatile Random Access Memory Cell Research Articles

Designing MoS2 channel properties for analog memory in neuromorphic applications

In this paper, we introduce analog nonvolatile random access memory cells for neuromorphic computing. The analog memory cell MoS2 channel is designed based on the simulation model including Fowler–Nordheim tunneling through a charge-trapping stack, trapping process, and transfer characteristics to describe a full write/read circle. 2D channel materials provide scaling to higher densities as well as preeminent modulation of the conductance by the accumulated space charge from the oxide trapping layer. In this paper, the main parameters affecting the distribution of memory states and their total number are considered. The dependence of memory state distribution on channel doping concentration and the number of layers is given. In addition, how the nonlinearity of memory state distribution can be overcome by variation of operating conditions and by applying pulse width modulation to the bottom gate voltage is also shown.

Integration of Quantum Dot Gate (QDG) in SWS-FETs for Multi-Bit Logic and QD-NVRAMs for Distributed In-Memory Computing

Compared to multi-valued logic (MVL) with conventional 2-state FETs with a single threshold, MVL computing architectures, based on 4-state SWS (Spatial wavefunction switched) and QDG (quantum dot gate)-FETs having multiple thresholds, results in reduced device count, higher clock (CLK) speed, and lower power consumption. We have experimentally shown multi-state characteristics in SWS-FETs as well as QDG-FETs. This paper presents a novel QDG-SWS-FET that: (1) functions as a multi-bit FET for efficient low-power logic, (2) can be configured as a quantum dot (QD) nonvolatile random access memory (NVRAM), and (3) is suitable for in-memory MVL computing architecture that are compatible with sub-7nm technology nodes. A QDG-SWS-FET with the addition of a control gate dielectric layer functions as a NVRAM cell. Furthermore, it is shown that one single SWS-QD-NVRAM cell gives the functionality of a 1-bit NAND. We have developed circuit/device models and performed quantum simulations for novel multi-layer quantum dot/quantum well FETs and NVRAMs. Our simulations have shown 4-states/2-bit output-input transfer characteristics in SWS-CMOS inverters and NAND gates using two Si/SiGe quantum well channels.

Ferroelectric-Gated Nanoelectromechanical Nonvolatile Memory Cell

A ferroelectric-gated nanoelectromechanical (NEM) nonvolatile random-access memory cell [negative capacitance (NC)-NEM memory] is proposed and investigated. By adjusting the structural parameters of the NEM relay, the pull-in voltage of the NC-NEM memory cell can be reduced, and its pull-out voltage can even become negative. Hence, an NEM relay with a ferroelectric layer in the gate stack can be used as a nonvolatile random-access memory cell. Herein, the device design and operational principles for read/program/erase are introduced in detail. The program/erase voltage and the program delay time of the NC-NEM memory cell have been quantitatively estimated.

Quantum Dot Floating Gate Nonvolatile Random Access Memory Using Ge Quantum Dot Channel for Faster Erasing

This paper presents an approach to enhance floating gate quantum dot nonvolatile random access memory (QDNVRAM) cells in terms of higher-speed and lower-voltage Erase not possible with conventional floating gate nonvolatile memories. It is achieved by directly accessing the floating gate layer with a Ge quantum dot access channel via an additional drain (D2) during the Erase and/or Write operation. Quantum mechanical simulations in GeOx-cladded Ge quantum dot layers functioning as the floating gate as well access channel to facilitate Erase and Write are presented. Experimental data on fabricated long channel nonvolatile random access memory cell with SiOx-cladded Si dots is presented. Quantum simulations show lower voltage operation for GeOx-cladded Ge QD floating gate than SiOx-cladded Si dots. The Erase time is orders of magnitude faster than flash and is comparable to competing NVRAMs.

Ferroelectric random access memory based on one-transistor–one-capacitor structure for flexible electronics

We have demonstrated a low temperature process for a ferroelectric non-volatile random access memory cell based on a one-transistor–one-capacitor (1T1C) structure for application in flexible electronics. The n-channel thin film transistors (TFTs) and ferroelectric capacitors (FeCaps) are fabricated using cadmium sulfide (CdS) as the semiconductor and poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer as the ferroelectric material, respectively. The maximum processing temperature for the TFTs is 100°C and 120°C for the FeCaps. The TFT shows excellent access control of the FeCap in the 1T1C memory cell, and the stored polarization signals are undisturbed when the TFT is off. The fabricated 1T1C memory cell was also evaluated in a FRAM circuit. The memory window on the bit line was demonstrated as 2.3V, based on the 1T1C memory cell with a TFT having dimensions of 80μm/5μm (W/L) and a FeCap with an area of 0.2×10−3cm2 using a bit line capacitor of 1nF pre-charged at 17.2V. The 1T1C memory cell is fabricated using photolithographic processes, allowing the integration with other circuit components for flexible electronics systems.

Samarium modified strontium bismuth niobate: Synthesis and ferroelectro-magnetic property evaluation

SrBi 2Nb 2O 9 (SBN) is an attractive ferroelectric material that is being considered in non-volatile random access memory cells. This study reports the effects of doping SBN at the Bi sites by the rare earth element Sm in the concentration range corresponding to x = 0–1 in the formula of SrBi 2− x Sm x Nb 2O 9. A solid-state double sintering method is adopted to synthesize and sinter the compounds starting from raw materials. It is shown that the crystal structure of SBN is retained but with slight changes to the lattice parameter. The sintered density, electric polarization and magnetization are enhanced by Sm addition. This system could be considered ferroelectromagnetic in nature.