Resistive switching effect in the planar structure of all-printed, flexible and rewritable memory device based on advanced 2D nanocomposite of graphene quantum dots and white graphene flakes

Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,Kim, Sowon,Choi, Kyung Hyun Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.33

<P>Pursuit of the most appropriate materials and fabrication methods is essential for developing a reliable, rewritable and flexible memory device. In this study, we have proposed an advanced 2D nanocomposite of white graphene (hBN) flakes embedded with graphene quantum dots (GQDs) as the functional layer of a flexible memory device owing to their unique electrical, chemical and mechanical properties. Unlike the typical sandwich type structure of a memory device, we developed a cost effective planar structure, to simplify device fabrication and prevent sneak current. The entire device fabrication was carried out using printing technology followed by encapsulation in an atomically thin layer of aluminum oxide (Al<SUB>2</SUB>O<SUB>3</SUB>) for protection against environmental humidity. The proposed memory device exhibited attractive bipolar switching characteristics of high switching ratio, large electrical endurance and enhanced lifetime, without any crosstalk between adjacent memory cells. The as-fabricated device showed excellent durability for several bending cycles at various bending diameters without any degradation in bistable resistive states. The memory mechanism was deduced to be conductive filamentary; this was validated by illustrating the temperature dependence of bistable resistive states. Our obtained results pave the way for the execution of promising 2D material based next generation flexible and non-volatile memory (NVM) applications.</P>

Effect of device structure on the resistive switching characteristics of organic polymers fabricated through all printed technology

Muhammad Muqeet Rehman,양봉수,양영진,Khasan S. Karimov,최경현 한국물리학회 2017 Current Applied Physics Vol.17 No.4

Developments in organic bi-stable non-volatile memory devices have shown that organic materials are essential for the next generation of electrical memory unit owing to their low cost, high flexibility and large scalability. This study depicts an important aspect of organic memory devices by observing the effect of changing device structure on its switching characteristics. Memory devices with a bilayer and bulk-heterojunction structure were fabricated through an all printed technology by utilizing two organic polymers such as MEH: PPV and PMMA. Silver (Ag) was selected as the top and bottom electrode due to its high conductivity and easy processing. Though identical polymers were used in both device structures, but interestingly change in structure caused change in properties. It was observed that bilayer structure had much higher switching ratio and stability against various biasing cycles as compared to its bulk-heterojunction counterpart. Superior switching characteristics of bilayer structure were due to the presence of a well-defined interface between both polymers. Bulk-heterojunction device suffers the drawback of phase separation in a single organic layer between the two polymers.

Highly flexible and electroforming free resistive switching behavior of tungsten disulfide flakes fabricated through advanced printing technology

Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,Doh, Yang Hoi,Choi, Kyung Hyun Institute of Physics 2017 Semiconductor science and technology Vol.32 No.9

<P>Tungsten disulfide (WS<SUB>2</SUB>) is a transition metal dichalcogenide that differs from other 2D materials such as graphene owing to its distinctive semiconducting nature and tunable band gap. In this study, we have reported the structural, electrical, physical, and mechanical properties of exfoliated WS<SUB>2</SUB> flakes and used them as the functional layer of a rewritable bipolar memory device. We demonstrate this concept by sandwiching few-layered WS<SUB>2</SUB> flakes between two silver (Ag) electrodes on a flexible and transparent PET substrate. The entire device fabrication was carried out through all-printing technology such as reverse offset printing for patterning bottom electrodes, electrohydrodynamic (EHD) atomization for depositing functional thin film and EHD patterning for depositing the top electrode respectively. The memory device was further encapsulated with an atomically thin layer of aluminum oxide (Al<SUB>2</SUB>O<SUB>3</SUB>), deposited through a spatial atmospheric atomic layer deposition system to protect it against a humid environment. Remarkable resistive switching results were obtained, such as nonvolatile bipolar behavior, a high switching ratio (∼10<SUP>3</SUP>), a long retention time (∼10<SUP>5</SUP> s), high endurance (1500 voltage sweeps), a low operating voltage (∼2 V), low current compliance (50 <I>μ</I>A), mechanical robustness (1500 cycles) and unique repeatability at ambient conditions. Ag/WS<SUB>2</SUB>/Ag-based memory devices offer a new possibility for integration in flexible electronic devices.</P>

자체전원공급 가능한 시스템을 위한 유연한 저전력 저항 메모리 소자

Muhammad Muqeet Rehman,Hafiz Mohammad Mutee ur Rehman,Shenawer Ali Khan,Muhammad Saqib,Woo Young Kim 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

최근 유기 비휘발성 메모리 장치는 주목받고 있다 1, 2. 본 연구에서, 두 고분자 물질(오렌지 염료, 폴리 3-헥실티오핀)의 합성물로 제작된 비휘발성 메모리 소자를 보고한다. 이 메모리 소자는 유연기판 상에 은(Ag)/유기복합체/은(Ag)의 샌드위치 구조를 가지도록 제조되었다. 제작된 메모리 소자는 -1.5V에서 +1.5V 까지의 동작전압 범위에서 전류 상한선을 1mA를 가지도록 작동하였고, 그 결과 저전력소모 동작이 가능하게 되었다. 또한 100 번 이상의 반복 측정에서도 고저항 상태와 저저항 상태가 서로 간섭하지 않고 일정한 동작을 유지하였으며, 4시간 이상 연속 동작에서도 정상 동작하였음을 확인하였다. 이 메모리 소자의 동작 메커니즘은 공간전하제한 전류(SCLC) 메커니즘으로 작동함을 이중로그 곡선으로부터 확인할 수 있었고, 오렌지 염료를 추가할수록 메모리동작을 위한 문턱전압의 크기가 감소함을 확인하였다. 폴리 3-헥실티오핀 기반의 기존 연구결과에 비해 굽힘반경 5cm 범위까지 25 번의 굽힘측정에서도 안정적인 결과를 나타내었다. 본 연구 성과는 유기물질을 기반으로 하는 고신뢰성 저전력 메모리 소자를 위한 중요한 진전으로 평가되며, 나노발전소자와도 호환가능한 자체전력공급 가능한 시스템의 중요한 요소로서 기여할 것으로 기대된다. Organic nonvolatile memory devices are of significant interest these days^1,2. In this study we have reported the non-volatile memory behavior of an organic composite based on two polymers i.e. orange dye (OD) and poly(3-hexylthiophene-2,5-diyl) (P3HT). This memory device was fabricated on flexible substrate for the possible application of wearable electronics with a sandwiched structure of silver (Ag)/P3HT-OD/Ag. This device exhibited its memory behavior by applying a small voltage sweep of – 1.5 V to 1.5 V with a current compliance (CC) of 10^-3 A hence, resulting in low power consumption. The obtained electrical results were highly stable as the values of both high resistance state (HRS) and low resistance state (LRS) were not deteriorated for more than 100 voltage sweeps. The device was tested for nearly 4 h without any considerable deterioration in its electrical characteristics. The conduction mechanism of this device was based on space charge limited current (SCLC) model as depicted form the double logarithmic I-V curve. Addition of OD resulted in the reduction of threshold voltage (V_th) value due to its lower value of work function which provided an easy path for the charge carriers to move from one electrode to another electrode. Significant achievement of this work is that no other P3HT based RRAM device has been characterized for its mechanical robustness, but our memory device showed stable electrical results against 25 bending cycles in the bending diameter range of 15 cm to 5 cm. This device is a significant step forward towards achieving a next generation low power memory device based on organic materials. Also, this low-power device will be expected to combine with nanogenerator for self-powered system in future.

Fabrication of a recyclable bio-waste material based humidity sensor for multiple applications

Muhammad Muqeet Rehman,Hafiz Mohammad Mutee ur Rehman,Maryam Khan,Woo Young Kim 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.3

2D nanocomposite of hexagonal boron nitride nanoflakes and molybdenum disulfide quantum dots applied as the functional layer of all-printed flexible memory device

Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,ur Rehman, Mohammad Mutee,Kim, Hyun Bum,Doh, Yang Hoi,Choi, Kyung Hyun Elsevier 2018 Materials research bulletin Vol.105 No.-

<P><B>Abstract</B></P> <P>In this study, we have proposed a flexible, rewritable and nonvolatile memory device based on an advanced 2D nanocomposite of hexagonal boron nitride (hBN) flakes and molybdenum disulfide quantum dots (MoS<SUB>2</SUB> QDs). Complete device fabrication was carried out by using extremely simple and highly controllable all printed technology. The electrical characteristics exhibited by the as developed memory devices included the switching ratio, electrical endurance and retention time of ∼10<SUP>3</SUP>, 10<SUP>3</SUP> and 10<SUP>4</SUP> respectively. The device turned ON and OFF at the SET and RESET threshold voltages of +1.4 V and −1 V respectively. The obtained results of electrical and thermal characterizations exhibited that the switching ratio decreases via either increasing temperature (300 K–380 K) or device size (42 μm–100 μm) hence verifying the formation of conductive filament through the functional layer. Moreover, no major degradation in the switching characteristics was observed even after 1500 bending cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We have proposed a flexible, rewritable and NVM device based on an advanced 2D nanocomposite. </LI> <LI> 2D nanocomposite is synthesized by mixing hBN flakes and MoS<SUB>2</SUB> QDs. </LI> <LI> Entire device was fabricated through extremely simple and highly controllable printing technology. </LI> <LI> The RRAM device was tested electrically, mechanically, thermally and chemically. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of adding a polymer and varying device size on the resistive switching characteristics of perovskite nanocubes heterojunction

양영진,Muhammad Muqeet Rehman,Ghayas Uddin Siddiqui,나경환,최경현 한국물리학회 2017 Current Applied Physics Vol.17 No.12

Emerging resistive switching devices are believed to play a vital role in realizing ultra-dense nanocrossbar arrays for the next generation mass storage memory. This work reports the resistive switching effect in organic-inorganic hybrid nanocomposite of perovskite oxide zinc stannite nanocubes (ZnSnO3 NCs) and a polymer Poly(methyl methacrylate) (PMMA). The functional layer was sandwiched between indium tin oxide (ITO) and silver (Ag) electrodes on a flexible PET substrate. The obtained electrical results clearly exhibited that the addition of PMMA in ZnSnO3 NCs enhanced electrical endurance (500 biasing cycles), retention time (~104 s), switching ratio (~103) and repeatability of our memory device. Moreover the effect of device size on the resistive switching characteristics of this hybrid nanocomposite is also explored by varying the diameter of top electrode. The whole device fabrication except bottom layer was done through all printed technology such as electrohydrodynamic atomization (EHDA) and inkjet reciprocating head. The developed memory device displayed characteristic bipolar, nonvolatile and rewritable memory behavior at a low operating voltage. The obtained results of chemical, structural, electrical and surface morphology are added to completely understand the impact of adding a polymer on the switching characteristics of perovskite NCs.

Significance of encapsulating organic temperature sensors through spatial atmospheric atomic layer deposition for protection against humidity

Mutee ur Rehman, Mohammad,Muqeet Rehman, Muhammad,Sajid, Memoon,Lee, Jae-Wook,Na, Kyoung Hoan,Ko, Jeong Beom,Choi, Kyung Hyun Springer-Verlag 2018 Journal of materials science Materials in electron Vol.29 No.17

Printing an ITO-free flexible poly (4-vinylphenol) resistive switching device

Ali, Junaid,Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,Aziz, Shahid,Choi, Kyung Hyun Elsevier 2018 PHYSICA B-CONDENSED MATTER - Vol.531 No.-

<P><B>Abstract</B></P> <P>Resistive switching in a sandwich structure of silver (Ag)/Polyvinyl phenol (PVP)/carbon nanotube (CNTs)-silver nanowires (AgNWs) coated on a flexible PET substrate is reported in this work. Densely populated networks of one dimensional nano materials (1DNM), CNTs-AgNWs have been used as the conductive bottom electrode with the prominent features of high flexibility and low sheet resistance of 90 Ω/sq. Thin, yet uniform active layer of PVP was deposited on top of the spin coated 1DNM thin film through state of the art printing technique of electrohydrodynamic atomization (EHDA) with an average thickness of 170 ± 28 nm. Ag dots with an active area of ∼0.1 mm<SUP>2</SUP> were deposited through roll to plate printing system as the top electrodes to complete the device fabrication of flexible memory device. Our memory device exhibited suitable electrical characteristics with OFF/ON ratio of 100:1, retention time of 60 min and electrical endurance for 100 voltage sweeps without any noticeable decay in performance. The resistive switching characteristics at a low current compliance of 3 nA were also evaluated for the application of low power consumption. This memory device is flexible and can sustain more than 100 bending cycles at a bending diameter of 2 cm with stable HRS and LRS values. Our proposed device shows promise to be used as a future potential nonvolatile memory device in flexible electronics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Resistive switching in Ag/ PVP/CNTs-AgNWs coated on a flexible PET substrate. </LI> <LI> Potential of CNTs-AgNWs to replace ITO as the bottom electrode in memory devices. </LI> <LI> All printing technology used for the fabrication of proposed memory device. </LI> <LI> Electrical and mechanical robustness of the proposed bottom electrode. </LI> <LI> Display of promising retention, electrical endurance and mechanical strength. </LI> </UL> </P>

Encapsulation of polyvinyl alcohol based flexible temperature sensor through spatial atmospheric atomic layer deposition system to enhance its lifetime

Kim, Soo Wan,Rehman, Muhammad Muqeet,Sajid, Memoon,Rehman, Mohammad Mutee ur,Gul, Jahanzeb,Jo, Jeong Dai,Choi, Kyung Hyun Elsevier 2019 THIN SOLID FILMS - Vol.673 No.-

<P><B>Abstract</B></P> <P>Printed organic sensors are of significant importance owing to their simplicity, low cost, easy fabrication and solution processability. However, organic sensors often suffer from the drawback of performance degradation when exposed to ambient environment. In this study, polyvinyl alcohol (PVA) is used as the functional layer of a temperature sensor and is encapsulated by aluminum oxide (Al<SUB>2</SUB>O<SUB>3</SUB>) deposited through spatial atmospheric atomic layer deposition system (SAALD). The encapsulating layer of Al<SUB>2</SUB>O<SUB>3</SUB> was pure, atomically thin and highly reliable. Fabricated organic temperature sensor is based on a conductive and uniform interdigitated pattern deposited on a flexible polyethylene naphthalate substrate through advanced printing technology of reverse offset. Thin film of PVA is used as the temperature sensitive functional layer deposited through electrohydrodynamic atomization followed by Al<SUB>2</SUB>O<SUB>3</SUB> encapsulation. The developed sensors were tested in the temperature range of 25 °C to 90 °C with relative humidity reaching up to 75% relative humidity. The obtained results exhibited that Al<SUB>2</SUB>O<SUB>3</SUB> encapsulation deposited through SAALD significantly enhanced the linearity, repeatability, endurance (50 cycles), retention (2 months) and lifetime of PVA based temperature sensor as compared with the non-encapsulated sensor hence, protecting the organic device from performance degradation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lifetime of organic temperature sensor has been enhanced through encapsulation. </LI> <LI> Electrical, mechanical, chemical, and morphological characterizations are included. </LI> <LI> The device is encapsulated with Al<SUB>2</SUB>O<SUB>3</SUB> thin film deposited through SAALD system. </LI> <LI> Encapsulated sensor displayed better results than non-encapsulated sensor. </LI> <LI> The obtained results were highly stable and reproducible. </LI> </UL> </P>