Highly durable and flexible memory based on resistance switching

doi:10.1016/j.sse.2009.10.021

Solid-State Electronics

Volume 54, Issue 4, April 2010, Pages 392-396

https://doi.org/10.1016/j.sse.2009.10.021 Get rights and content

Abstract

Resistance random access memory (RRAM) consisting of stacked Al/TiO_x/Al structure is demonstrated on a flexible and transparent substrate. To improve cell to cell uniformity, TiO_x formed by atomic layer deposition is used for resistive switching material. The simple cross-bar structure of the RRAM and good ductility of aluminum electrode results in excellent flexibility and mechanical endurance. Particularly, bipolar and unipolar resistive switching (BRS, URS) behavior appeared simultaneously were investigated. Depending on the current compliance, BRS or URS could be selectively observed. Furthermore, the permanent transition from BRS to URS was observed with a specific current compliance. To understand this transition behavior, the γ-ray irradiation effect into resistive switching is primarily investigated.

Introduction

Many flexible devices have been developed for electronic paper, transistors for displays, sensors, solar cells, and organic light emitting diodes [1], [2], [3]. Based on this technological trend, the need for a flexible type of memory will also increase to support these flexible electronic devices, similar to the role of flash memory in solid state electronics today. However, most types of flexible memories have been based on organic materials [4], [5], [6]. Although organic memory shows good flexibility, its performance cannot match that of conventional flash memory. Additionally, the fabrication process of organic memory is complicated by the requirements of controlled external conditions. These limitations require additional efforts to improve memory performance and increase processing costs.

Recently, resistance random access memory (RRAM) has attracted great attention due to its potential to replace flash memory in next-generation nonvolatile memory applications [7], [8]. The resistive switching effect is observed as a result of various insulating materials that consist of CMOS process compatible inorganic materials. In addition, the current–voltage (I–V) characteristics of the simple metal–insulator–metal (MIM) structure exhibit rapid switching speeds and distinctive changes of the resistance between the high resistance state (HRS) and the low resistance state (LRS).

In the present study, the fabrication of a flexible type of RRAM is reported. In an earlier work by the authors, plasma oxidized aluminum [9] and sol–gel derived zinc oxide [10] were used as resistive switching material for flexible type RRAM. On the other hand, in this study, atomic layer deposition (ALD) process is used to improve cell to cell uniformity and for realistic feasibility in flexible memory applications using existing semiconductor technology. The structural simplicity and good ductility of aluminum electrode result in advantages that include good flexibility, mechanical endurance, and durability. In addition, the resistive switching mechanism is investigated by means of a permanent transition from bipolar resistive switching (BRS) to unipolar resistive switching (URS) in TiO_x films, as understood through γ-ray irradiation effects.

Section snippets

Device fabrication

The flexible RRAM was fabricated on the flexible and transparent substrate of polyethersulfone (PES), as shown in Fig. 1. The PES film was glued onto a silicon wafer with polyimide. Aluminum with a thickness of 150 nm was used for the top and bottom electrodes. The electrodes were patterned by conventional photolithography ranging from 2 × 2 to 100 × 100 μm². TiO_x of 10 nm thickness was used to formulate the resistive switching material. The TiO_x films were deposited using plasma-enhanced atomic layer

Switching performance

Fig. 2a shows the typical switching characteristics of Al/TiO_x/Al that produces BRS. Bias sweeps were conducted in the direction 0 V → −3 V → 0 V → 3 V → 0 V. The current increased sharply at a negative bias (V_SET) and switched from HRS to LRS. The LRS remains during the voltage sweep back at a positive bias less than V_RESET. The resistance ratio (R_off/R_on) between HRS and LRS is larger than 50 at V_READ = 0.2 V under a compliance current of 500 μA. Fig. 2b shows the measured retention characteristics of the

Flexibility and mechanical endurance

Good mechanical flexibility is crucial for applications in flexible electronics. The level of mechanical endurance was evaluated by performing a substrate bending test in which both tensile and compressive stresses were induced, as shown in Fig. 7a. A vibrator was used to induce substrate bending 4 times/s for the total of 10⁵ bends. Even at 10⁵ bends, the R_off/R_on value was unchanged. In addition, the devices exhibited good flexibility, as shown in Fig. 7b. In the flexibility test, severe

Conclusions

RRAM device was fabricated and showed reliable endurance and retention characteristics, even on a flexible substrate. The transition behavior from BRS to URS was understood with the aid of γ-irradiation. This flexible type of RRAM is attractive for low-cost and wearable devices and may be suitable in flexible displays.

Acknowledgements

This research was supported by a Grant (08K1401-00210) from the Center for Nanoscale Mechatronics & Manufacturing, one of the 21st Century Frontier Research Programs supported by the Korea Ministry of Education, Science and Technology (MEST).

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Citation Excerpt :
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Silver nanoparticles (Ag NPs) blended with poly(ethylene-co-vinyl acetate) (EVA) were used as an active layer to fabricate flexible and fully transparent memory devices by using the spin-coating method followed by the thermal roll lamination technique with the structure of ITO/EVA:Ag NPs/ITO. The devices exhibited a non-volatile write-once-read-many-times (WORM) memory type and possessed current bi-stability with ON/OFF current ratio within the range of 10⁴-10⁵ at a reading voltage of +1 V. The data continuous read operations reached more than 10 h, which revealed the stability of the memory devices over a long period of time. The conduction mechanisms of the memory device could be explained by theoretical models and proposed by electron trapping at the trapping center of Ag NPs inside the EVA matrix. In addition, the memory device showed a fast response of 231 ns and was fully transparent with maximum transmittance of the device at 83.2%. Further, the devices could be operated under the bending condition of more than 0.83% strain.

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Highly durable and flexible memory based on resistance switching

Abstract

Introduction

Section snippets

Device fabrication

Switching performance

Flexibility and mechanical endurance

Conclusions

Acknowledgements

Electronic paper: flexible active-matrix electronic ink display

Nature

Fabrication of fully transparent nanowire transistors for transparent and flexible electronics

Nat Nanotechnol

Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors

Nat Mater

A flexible polymer memory device

Org Electron

A polymer/semiconductor write-once read-many-times memory

Nature

High-performance solution-processed polymer ferroelectric field-effect transistors

Nat Mater

Resistive switching of aluminum oxide for flexible memory

Appl Phys Lett

Resistive switching characteristics of sol–gel zinc oxide films for flexible memory applications

IEEE Trans Electron Dev

Reproducible hysteresis and resistive switching in metal–CuxO–metal heterostructures

Appl Phys Lett

Field-induced resistive switching based on space-charge-limited current

Appl Phys Lett

Current injection in solids

Reproducible hysteresis and resistive switching in metal–Cu_xO–metal heterostructures