Search query: Logic-in-memory based on an atomically thin semiconductor

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abstract: The growing importance of applications based on machine learning is driving the need to develop dedicated, energy efficient electronic hardware. Compared with von Neumann architectures, brain inspired in memory computing uses the same basic device structure for logic operations and data storage1 3, thus promising to reduce the energy cost of data centric computing significantly4. While there is ample research focused on exploring new device architectures, the engineering of material platforms suitable for such device designs remains a challenge. Two dimensional materials5,6 such as semiconducting MoS2 could stand out as a promising candidate to face this obstacle thanks to their exceptional electrical and mechanical properties7 9. Here, we explore large area grown MoS2 as an active channel material for developing logic in memory devices and circuits based on floating gate field effect transistors (FGFET) The conductance of our FGFETs can be precisely and continuously tuned, allowing us to use them as building blocks for reconfigurable logic circuits where logic operations can be directly performed using the memory elements. After demonstrating a programmable NOR gate, we show that this design can be simply extended to implement more complex programmable logic and functionally complete sets of functions. Our findings highlight the potential of atomically thin semiconductors for the development of next generation low power electronics.
author_names: Guilherme Migliato Marega

Yanfei Zhao

Ahmet Avsar

Zhenyu Wang

Mukesh Tripathi

Aleksandra Radenovic

Andras Kis
title: Logic in Memory Based on an Atomically Thin Semiconductor
venue: Nature
year: 2020

abstract: Silicon based semiconductor technology is facing more and more challenges to continue the Moore's law due to its fundamental scaling limitations. To continue the pace of progress of device performance for both logic and memory devices, researchers are exploring new low dimensional materials, e.g. nanowire, nanotube, graphene and hexagonal boron nitride. Transition metal dichalcogenides (TMDs) are attracted considerable attention due their atomically thin nature and proper bandgap at the initial study. Recently, more and more interesting properties are found in these materials, which will bring out more potential usefulness for electronic applications. Competing with the silicon device performance is not the only goal in the potential path finding of beyond silicon. Low dimensional materials may have other outstanding performances as an alternative materials in many application realms. This thesis explores the potential of TMD based devices in memory and logic applications. For the memory application, TMD based vertical devices are fully studied. Two terminal vertical transition metal dichalcogenide (TMD) based memory selectors were firstly built and characterized, exhibiting better overall performance compared with some traditional selectors. Polymorphism is one of unique properties in TMD materials. 2D phase engineering in TMDs attracted great attention. While electric switching between semiconductor phase to metallic phase is the most desirable. In this thesis, electric field induced structural transition in MoTe2 and Mo1 xWxTe2 is firstly presented. Reproducible bipolar resistive random access (RRAM) behavior is observed in MoTe2 and Mo1 xWxTe2 based vertical devices. Direct confirmation of a phase transition from a 2H semiconductor to a distorted 2Hd metallic phase was obtained after applying an electric field. Set voltage is changed with flake thickness, and switching speed is less than 5 ns. Different from conventional RRAM devices based on ionic migration, the MoTe2 based RRAMs offer intrinsically better reliability and control. In comparison to phase change memory (PCM) based devices that operate based on a change between an amorphous and a crystalline structure, our MoTe2 based RRAM devices allow faster switching due to a transition between two crystalline states. Moreover, utilization of atomically thin 2D materials allows for aggressive scaling and high performance flexible electronics applications. Both of the studies shine lights on the new application in the memory field with two dimensional materials.For the logic application, the ultra thin body nature of TMDs allows for more aggressive scaling compared with bulk material silicon. Two aspects of scaling properties in TMD based devices are discussed, channel length scaling and channel width scaling. A tunability of short channel effects in MoS2 field effect transistor (FET) is reported. The electrical performance of MoS2 flakes is governed by an unexpected dependence on the effective body thickness of the device which in turn depends on the amount of intercalated water molecules that exist in the layered structure. In particular, we observe that the doping stage of a MoS2 FET strongly depends on the environment (air/vacuum) For the channel width scaling, the impact of edge states in three types of TMDs, metallic Td phase WTe2 as well as semiconducting 2H phase MoTe2 and MoS2 were explored, by patterning thin flakes into ribbons with varying channel widths. No obvious charge depletion at the edges is observed for any of these three materials, which is different from what has been observed in graphene nanoribbon devices.
author_names: Feng Zhang
title: Transition Metal Dichalcogenide Based Memory Devices and Transistors
year: 2019

abstract: Metal oxide semiconductor field effect transistors (MOSFET) based on two dimensional (2D) semiconductors have attracted extensive attention owing to their excellent transport properties, atomically thin geometry, and tunable bandgaps. Besides improving the transistor performance of individual device, lots of efforts have been devoted to achieving 2D logic functions or integrated circuit towards practical application. In this review, we discussed the recent progresses of 2D based logic circuit. We will first start with the different methods for realization of n type metal oxide semiconductor (NMOS) only (or p type metal oxide semiconductor (PMOS) only) logic circuit. Next, various device polarity control and complementary metal oxide semiconductor (CMOS) approaches are summarized, including utilizing different 2D semiconductors with intrinsic complementary doping, charge transfer doping, contact engineering, and electrostatics doping. We will discuss the merits and drawbacks of each approach, and lastly conclude with a short perspective on the challenges and future developments of 2D logic circuit.
author_names: Lingan Kong

Yang Chen

Yuan Liu
title: Recent progresses of NMOS and CMOS logic functions based on two dimensional semiconductors
venue: Nano Research
year: 2020

abstract: Abstract Piezotronic and piezo phototronic effects have attracted much attention as promising approaches for active electronic/optoelectronic devices. However, the piezotronic and piezo phototronic devices in previous reports are mainly based on nanowires or two dimensional transition metal dichalcogenides that have size of several micrometers along the polarization direction. As the fast development of nanoelectronics and nano optoelectronics, exploring the piezotronic effect and piezo phototronic effect at nanometer scale for ultrathin nanodevices and nanosystems is valuable. Here, we investigated the piezotronic and piezo phototronic effects of atomically thin ZnO nanosheet, and revealed the dominant mechanism. Experiments were performed on the atomically thin ZnO field effect transistor, which showed enhanced electronic transport characteristic under pressure. Theoretical analysis revealed that the change of electronic transport behavior was caused by pressure induced modulation on the effective thickness of the transport channel and the Schottky barrier between ZnO and contact electrodes. Meanwhile, the atomically thin ZnO film exhibited enhanced response to ultraviolet light under pressure with a high photoresponsivity of 300 AW 1 (Vds 2 V) This value was improved 230% than the response of the same device under strain free condition, and more than 103 times higher than the performance of commercial ultraviolet photodetectors, indicating the effectiveness of piezo phototronic effect in nanoscale. This study shows great promises of the ultrathin devices based on piezotronic and piezo phototronic effects, which paves the way for atomically thin semiconductors with out of plane piezoelectricity for applications in novel electronics/optoelectronics.
author_names: Chunhua An

Longfei Wang
title: Piezotronic and piezo phototronic effects of atomically thin ZnO nanosheets
year: 2021

abstract: The self heating effect (SHE) in top gate In Ga Zn O (IGZO) thin film transistors (TFTs) was examined systematically using short electrical pulse measurement methods. The temperature dependence of the pulse measurements of IGZO TFTs revealed a significant increase in temperature during the measurements, suggesting that conventional measurements can overestimate the device performance significantly. The effective temperature was introduced and extracted for IGZO TFTs at various heating powers and ambient temperatures. The short sampling time was determined to be a key in characterizing the intrinsic device properties that are not influenced by the SHE. The cooling behavior after self heating was also examined using multipulse measurements. Because heating and cooling are significant even in a very short time, it is essential to consider the operation condition of the devices when characterizing TFTs to estimate the precise performance and reliability in a real operation.
author_names: Manh-Cuong Nguyen

Nuri On

Hyungmin Ji

An Hoang-Thuy Nguyen

Sujin Choi

Jonggyu Cheon

Kyoung-Moon Yu

Seong-Yong Cho

Jinhyun Kim

Sangwook Kim

Jaekyeong Jeong

Rino Choi
title: Electrical Characterization of the Self Heating Effect in Oxide Semiconductor Thin Film Transistors Using Pulse Based Measurements
venue: IEEE Transactions on Electron Devices
year: 2018

abstract: Abstract Dilute magnetic semiconductors have shown a great encouragement from the technological point of view owing to their potential application in multiple spintronics, such as spin light emitting diode, spin valve transistor, logic device, nonvolatile memory and ultrafast optical switches. Here, we report on the synthesis of Zn 1 x Cr x O (0.01<=x<=0.09) thin films grown on Si (111) substrate via 1,2 dihydroxyethane modified sol gel dip coating technique for spintronic applications. The influence of partial substitution of Cr ions into the Zn sites on the chemical composition, morphology, crystal structure, and magnetic properties of the prepared films was investigated by the X ray diffraction (XRD) atomic force microscopy (AFM) high resolution transmission electron microscopy (HR TEM) dispersive X ray spectroscopy (EDS) electron diffraction (SAED) X ray electron spectroscopy (XPS) and vibrating magnetometer (VSM) A single phase and highly crystalline films are obtained. These films showed room temperature ferromagnetism at all Cr ions concentration. The Zn 0.95 Cr 0.05 O film showed a remarkable giant magnetic moment of 2.17m B at room temperature. This is the highest magnetic moment value ever achieved among all derived transition elements doped ZnO based dilute magnetic semiconductors till the date.
author_names: Waleed E Mahmoud
title: Observation of room temperature ferromagnetism with giant magnetic moment based on Zn1 xCrxO thin films grown on Si(111) substrate via 1,2 dihydroxyethane modified sol gel dip coating technique
year: 2016

abstract: DOI: 10.1002/aelm.201800308 body.[11 13] As a result, transistors based on TMDs are expected to show superior performances, which means that the application of TMDs can be broadened to digital logic,[14,15] memory,[16,17] or next generation computation systems.[18,19] To fabricate complementary devices including nand p type field effect transistors (FETs) an efficient doping process should be developed and, in addition, the long term stability of these devices needs to be coupled.[20 25] Owing to its superior photoactivity, MoSe2 has recently been investigated for application in various fields, including energy storage, catalysis, and optoelectronic devices. Since the bandgap of MoSe2 is smaller than that of MoS2, a larger electrical conductivity can be expected in MoSe2 FETs.[26 29] Additionally, it has been reported that since the MoSe bond is more stable than the MoS bond, the possibility of defect formation at the oxide TMD channel interface is reduced, as a result of which, the noise current is lower in MoSe2 than MoS2. However, during the synthesis process of MoSe2 via chemical vapor transport (CVT) or chemical vapor deposition (CVD) uncontrolled defects states can be introduced in the MoSe2 flakes, because of involving the high temperature and pressure environment to produce a single crystal mineral TMD. Therefore, the synthesized MoSe2 FETs tend to randomly exhibit the characteristics of not only n type behavior but also ambipolar or p type behavior; as shown in previous results,[31,33 36] it has been reported that CVDor CVT grown MoSe2 FETs can be ambipolar, n dominant, or p dominant transistors depending on the growth conditions. To enable the integration of CVDor CVT synthesized MoSe2 in practical devices, these inhomogeneous characteristics of MoSe2 FETs should be unipolar. The present report demonstrates a process to achieve n doping of CVD grown multilayer MoSe2 FETs via a two step surface functionalization procedure that involves exposure to oxygen plasma followed by the deposition of an Al2O3 passivation layer using atomic layer deposition (ALD) The oxygen plasma treatment induces the formation of interfacial MoOx layer at MoSe2 and the reduction of hall current in all fabricated MoSe2 FETs, while the on current at n branch is nearly constant. Moreover, thin MoOx layer can provide nucleation sites with dangling bonds for the uniform deposition of ALD Al2O3. After the deposition of ALD Al2O3 on MoOx/MoSe2, Ion/Ioff ratio of MoSe2 FETs at n branch is enhanced by up to 9.6 times Molybdenum diselenide (MoSe2) has attracted attention as a potential semiconductor platform. However, the as synthesized MoSe2 field effect transistors (FETs) tend to exhibit the arbitrary properties of n type, p type, or ambipolar behavior due to the uncontrolled growth condition. Here, two step functionalization is proposed to achieve n doping effect and long term stability in chemical vapor deposition (CVD) grown MoSe2 FETs using oxygen plasma treatment followed by the deposition of an Al2O3 layer. After the two step surface functionalization procedure, three types of multilayer MoSe2 FETs are all converted to n type with the improvement of their electrical characteristics and stability; the n doped multilayer MoSe2 FETs exhibit an enhancement in field effect mobility from 12.23 to 31.57 cm2 V 1 s 1 and a 3 times higher Ion/Ioff, compared to pristine multilayer MoSe2 FETs. This enhancement of electric performance is attributed to the oxidation of topmost MoSe2 to interfacial MoOx with SeOx induced by the oxygen plasma treatment, as well as to the existence of fixed positive charges in deposited Al2O3. The functionalized devices exhibit excellent stability against stress, as confirmed with negative bias illumination stress tests for 7200 s. Moreover, an environmental stability test for 21 days reveals no degradation in electric performance of MoSe2 FETs.
author_names: Seongin Hong

Haelin Im

Young Ki Hong

Na Liu

Sunkook Kim

Jun Hong Park
title: n Type Doping Effect of CVD Grown Multilayer MoSe2 Thin Film Transistors by Two Step Functionalization
year: 2018

abstract: Abstract A high soluble dimeric perylene tetracarboxylic diimide 1 was fabricated into the thin solid films by means of quasi Langmuir Shafer (QLS) method. The structure and properties of the QLS films were comparatively studied with those of monomeric perylene tetracarboxylic diimide 2 by electronic absorption, fluorescence, polarized electronic absorption spectroscopy, X ray diffraction (XRD) and atomic force microscopy (AFM) Experimental results revealed the film crystallinity and general molecular order in the film of 1 are improved effectively in comparison with those of 2 due to the dimeric structure of 1 Electron mobilities as high as 0.03 cm 2 V 1 s 1 for the films of novel dimeric 1 are achieved, which is much better than that of monomeric 2 (5.0 x 10 7 cm 2 V 1 s 1 In particular, the electronic mobility of 1 only slightly decreased after exposure to air and remained almost unchanged after 90 days, which is attributed to molecular packing effects including close stacking of dimeric PDI units and segregation effects imparted by the 2 N,N di(n butyl) amino 4,6 dihydrazine 1,3,5 trazine unites as well as relatively low lying LUMO energy level. The present result represents not only the first example of solution processed, air stable dimeric PDI based n type OFET, but more importantly provides an efficient way to enhance the performance of air stable n channel organic semiconductors through intra molecular bonding to pre organizing the p conjugated organic molecules into a rigid co facially stacked structure.
author_names: Nianshuai An

Yanan Shi

Junqiang Feng

Dapan Li

Jian Gao

Yanli Chen

Xiyou Li
title: N channel organic thin film transistors based on a soluble cyclized perylene tetracarboxylic diimide dimer
year: 2013

abstract: Monolayer transition metal dichalcogenides (TMDs) with a direct bandgap are suitable for various optoelectronic applications such as ultrathin light emitters and absorbers. However, their weak light absorption caused by the atomically thin layer hinders more versatile applications for high optical gains. Although plasmonic hybridization with metal nanostructures significantly enhance light matter interactions, the corrosion, and instability of the metal nanostructures and the undesired effects of direct metal semiconductor contact act as obstacles to its practical application. Herein, we propose a dielectric nanostructure for plasmon enhanced light matter interaction of TMDs. TiO2 nanowires (NWs) as an example, are hybridized with MoS2 monolayer on various substrates. The structure is implemented by placing a monolayer MoS2 between a TiO2 NW for photonic scattering effect and metallic substrates with a spacer for the plasmonic Purcell effect. Here, the thin dielectric spacer is aimed at minimizing emission quenching from direct metal contact, while maximizing optical field localization in ultrathin MoS2 near TiO2 NW. An effective emission enhancement factor of ~22 is attained for MoS2 near the NW of the hybrid structure compared to the one without NWs. Our work is expected to facilitate a hybridized platform based on 2D semiconductors for high performance and robust optoelectronics via engineering dielectric nanostructures with plasmonic materials.
author_names: Jung Ho Kim

Hyun Seok Lee

Gwang Hwi An

Jubok Lee

Hye Min Oh

Jihoon Choi

Young Hee Lee
title: Dielectric Nanowire Hybrids for Plasmon Enhanced Light Matter Interaction in 2D Semiconductors.
venue: ACS nano
year: 2020

abstract: Monolayered, semiconducting molybdenum disulfide (MoS2) is of considerable interest for its potential applications in next generation flexible, wearable, and transparent photodetectors because it has outstanding physical properties coupled with unique atomically thin dimensions. However, there is still a lack of understanding in terms of the underlying mechanisms responsible for the photoresponse dynamics, which makes it difficult to identify the appropriate device design strategy for achieving a fast photoresponse time in MoS2 photodetectors. In this study, we investigate the importance of surface functionalization on controlling the charge carrier densities in a MoS2 monolayer and in turn the corresponding behavior of the photoresponse in relation to the position of the Fermi level and the energy band structure. We find that the p doping and n doping, which is achieved through the surface functionalization of the MoS2 monolayer, leads to devices with different photoresponse behavior. Specifically, the MoS2 devices with surface functional groups contributing to p doping exhibited a faster response time as well as higher sensitivity compared to that observed for the MoS2 devices with surface functional groups contributing to n doping. We attribute this difference to the degree of bending in the energy bands at the metal semiconductor junction as a result of shifting in the Fermi level position, which influences the optoelectronic transport properties as well as the recombination dynamics leading to a low dark and thus high detectivity and fast decay time. Based upon these findings, we have also demonstrated the broad applicability of surface functionalization by fabricating a flexible MoS2 photodetector that shows an outstanding decay time of 0.7 s, which is the fastest response time observed in flexible MoS2 detectors ever reported.
author_names: Sang Il Pak

A-Rang Jang

Juwon Lee

John Hee Hong

Paul Henri Giraud

Sanghyo Lee

Yuljae Cho

Geon-Hyoung An

Young-Woo Lee

Hyeon Suk Shin

Stephen M Morris

SeungNam Cha

Jung Inn Sohn

Jong Min Kim
title: Surface functionalization induced photoresponse characteristics of monolayer MoS2 for fast flexible photodetectors.
venue: Nanoscale
year: 2019