Resistive Switching Characteristics of a Pt Nanoparticle-Embedded SiO2-based Memory

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Resistive switching characteristics of a Pt nanoparticle-embedded

SiO

2

-based memory

Chih-Yi Liu

a,

⁎

, Jyun-Jie Huang

a

, Chun-Hung Lai

b

a

Department of Electronic Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan, ROC b_{Department of Electronic Engineering, National United University, Miaoli 360, Taiwan, ROC}

a b s t r a c t

a r t i c l e i n f o

Available online 5 April 2012 Keywords:

Resistive switching SiO2

Nanoparticle Memory

A Cu/Pt nanoparticle (Pt-NP)-embedded SiO2/Pt structure was fabricated to investigate its resistive switching

behavior. The resistive switching behavior may be explained by thefilament model with the electrochemical reaction. The Pt-NPs enhanced the local electricfield to facilitate the filament formation and to decrease the operating voltages. In addition, the non-uniform distribution of the electricfield caused the formation of a Cu filament on a Pt-NP, which decreased the switching dispersion. A simulation of the electric field in a Pt-NP embedded SiO2layer was used to investigate the influence of Pt-NPs on the resistive switching behavior.

1. Introduction

Recently, non-volatile memory (NVM) has attracted notable inter-est because it can retain information without a power supply. There-fore, NVM devices are widely used in portable electronic products. Flash memory is currently the mainstream NVM device. However, flash memory has several disadvantages such as a high operating voltage and a slow operating speed. Following the continuous device scaling, the thin tunneling oxide may lead to a large leakage current, which causes degradation of the retention time. Several devices, such as magnetic random access memory[1], ovonic unified memory[2], ferroelectric random access memory[3], and resistive random access memory (RRAM)[4], were proposed as suitable candidates for the next-generation of NVM applications. Among these devices, RRAM resistance can reversibly switch by DC voltages or voltage pulses. Several materials, such as CuxO [5], TiO2[6], NiO [7], and SiO2[8], were proposed for their various resistive switching behaviors. The resistive switching behaviors are influenced by the resistive layer, electrode material, and process parameters. In general, thermochem-ical reaction[9], electrochemical reaction[10], and valence change effect[11]are used to explain the resistive switching behaviors. The effects of the embedded nanoparticles in the resistive layer on the resistive switching behavior were recently investigated [12–14]. Chen et al. adopted the Ru nanocrystals within the resistive layer to improve the device yield and retention performance[12]. Tsai et al. proposed the Ni nanoparticle, which enhanced the local electric

ﬁeld for a thermochemical RRAM[14]. The Ni nanoparticles enhanced the local electricﬁeld, which reduced the switching dispersion. The effect of metal nanoparticles within the resistive layer on the resistive switching behaviors of an electrochemical RRAM has not been investigated.

In this study, we used a Cu/SiO2/Pt structure to investigate the electrochemical resistive switching. Pt nanoparticles (Pt-NPs) were embedded into the SiO2 layer to investigate the influence of the Pt-NPs on the resistive switching behavior of an electrochemical RRAM. The Pt-NPs enhanced the local electricfield near the Pt-NPs, which decreased the operating voltages. The non-uniform distribu-tion of the electricfield in the SiO2 layer confined the switching region, which stabilized the resistive switching, and thus reduced the switching dispersion. In addition, afinite element method was used to simulate the electricfield within the SiO2layer to investigate the effects of Pt-NPs on the resistive switching behaviors.

2. Experimental procedures

A 4 inch p-type silicon wafer was used as the process substrate. After a standard Radio Corporation of America (RCA) cleaning, a 200 nm SiO2layer was thermally grown to isolate the leakage current from the Si substrate. A 5 nm Ti adhesion layer and a 100 nm Pt layer were subsequently deposited by an electron-beam evaporator to fabricate the Pt/Ti/SiO2/Si substrate. Next, a 20 nm SiO2 layer was deposited by a radio frequency sputter. A 2.5 nm Pt layer was depos-ited by an electron-beam evaporator. The thickness of the Pt_ﬁlms was controlled by an in situ quartz crystal oscillator. Subsequently, Pt nanoparticles (Pt-NPs) were formed by annealing at 500 °C for 60 s in nitrogen ambience. A 20 nm SiO2was subsequently deposited

Thin Solid Films 529 (2013) 107–110

⁎ Corresponding author. Tel.: +886 7 381 4526; fax: +886 7 381 1182. E-mail address:[email protected](C.-Y. Liu).

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Thin Solid Films

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uniform resistive switching of SET process. Therefore, the switching dispersion of the RESET process also decreased.

For a Cu-doped SiO2-based RRAM, long-term thermal annealing was required to diffuse Cu atoms into the SiO2layer to improve the switching dispersion[21]. Long-term thermal annealing may result in a large thermal budget and cause difﬁculty in multilayer integra-tion[22]. In this study, the Cu/Pt-NP-embedded SiO2/Pt structure did not require long-term thermal annealing, which lowered the thermal budget of the device fabrication. In addition, the Pt-NP within the SiO2layer reduced the switching dispersions and decreased the operating voltage. Furthermore, the forming voltage was nearly consistent to the SET voltage. Therefore, the additional circuit of the forming process was unnecessary.

4. Conclusions

We fabricated a Cu/Pt-NP-embedded SiO2/Pt structure to investi-gate the inﬂuence of the Pt-NPs on the resistive switching behavior.

For the IRS, the conduction mechanism was dominated by Schottky emission in the low electricfield and was dominated by Frenkel– Poole in the high electric_{field. For the LRS and the HRS, the} conduc-tion mechanism was dominated by Ohmic conducconduc-tion. The switching mechanism was due to the electrodeposition and dissolution of a Cu filament near the Cu/SiO2layer. The embedded Pt-NP enhanced the local electricfield between the Cu electrode and a Pt-NP. Therefore, the enhanced electricfield accelerates the Cu dissolution at the Cu electrode and the electrodeposition on the Pt-NP. After the Cu

ﬁla-ment formed above the Pt-NP, the electric ﬁeld was enhanced

below the Pt-NP. Subsequently, another Cufilament formed below the Pt-NP to connect the whole Cu-conductingfilament. The Pt-NP enhanced the localfield, which decreased the operating voltages. The non-uniform distribution of the electricfield reduced the switch-ing dispersion. The Pt-NP embedded SiO2-based device also lowered the thermal budget of the fabrication process, which bene_{fited the} multilayer integration.

Acknowledgements

The authors thank the National Science Council of R.O.C. forﬁnancial supports under project No. NSC 99-2221-E-151-065 and 100-2221-E-151-008, and the facility support from National Nano Device Laboratories.

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