Contents lists available at ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi Investigation of resistive switching in PVP and ultra-thin HfOx based bilayer hybrid RRAM Ishan Varun, Deepak Bharti, Ajay Kumar Mahato, Vivek Raghuwanshi, Shree Prakash Tiwari ⁎ Department of Electrical Engineering, Indian Institute of Technology Jodhpur, Jodhpur, Rajasthan 342037, India ARTICLE INFO Keywords: Conductive bridge resistive random access memories (CBRAMs) Resistive switching Hybrid CBRAM Electro-migration Pinholes Conductive filament ABSTRACT Hybrid CBRAM devices based on PVP/HfO x bilayer were investigated for their switching performance. A reliable and low voltage bipolar resistive switching operation was observed in these devices with repeatability of 300 cycles, I on /I off of 80, set (V set ) and reset (V reset ) voltages of 1.03 V and -0.68 V, retention time of 7200 s, and switching endurance of > 2000 cycles in devices with 2.5 wt% PVP concentration. Low device-to-device varia- tion was observed with 10 devices tested showing nearly similar switching parameters. Weibull's distribution of V set and V reset voltages have indicated reliable switching performance in devices. The pinholes formation in PVP layer guides the confined growth and dissolution of Ag conductive filament (CF) in the bilayer structure resulting in a stable, reliable and low voltage switching operation. PVP film roughness and pinholes depth have shown downtrend with PVP concentration. During the set process, a CF formed across the electrodes constitutes of Ag atoms, due to pinholes assisted electro-migration of Ag ions. Whereas in the reset process, the diffused Ag + ions migrate back towards top electrode due to the electrochemical and joule-heating assisted rupture of CF in the PVP/HfO x bilayer structure. 1. Introduction Over the past ten years, profound research interest in the field of conductive bridge resistive random access memories (CBRAMs) has been developed due to its simple structure, easy fabrication, lower power consumption, scaling, integration capabilities with CMOS tech- nology, and multibit storage ability [1]. Resistive switching has been investigated in various inorganic and organic dielectrics such as like HfO 2 [2], Al 2 O 3 [3], Ta 2 O 5 [4], TiO 2 [5], ZnO [6], poly(methyl-me- thacrylate) [7], Cu:tetracyanoquinodimethane [8], polyvinyl alcohol [9], poly(4-vinylphenol) (PVP) [10], graphene oxide [11], and poly (vinylpyrrolidone) [12]. Switching mechanisms in these CBRAM de- vices have been found mainly due to electro-migration of electrode ions through the dielectrics or the oxygen vacancies in the oxide films [13,14]. Organic dielectrics based CBRAM devices are known for their excellent switching window whereas the metal oxide based CBRAMs are popular for their reliability, longer retention time and low voltage operation [1,15,16]. The qualities of each type of dielectric are ex- pected to evolve collectively in their hybrid stacks. Though there are various reports available on metal oxide based bilayer CBRAMs to ob- tain improved performance, only a few reports are available on organic dielectrics and their stacks [17–19]. Poly(4-vinylphenol) (PVP)/HfO x stack has resulted in devices with low operating voltage and uniform performance when used as gate dielectric in organic field effect tran- sistors (OFETs) and OFET based sensors, however the capabilities of this stack as an insulating medium in CBRAMs to obtain lower oper- ating voltages and uniform performance are yet to be examined [20]. In this paper, we report bipolar resistive switching in PVP/HfO x based low voltage and highly reliable hybrid CBRAM devices. The weibull distribution of set (V set ) and reset (V reset ) voltages indicates a reliable device performance. In addition, a low device-to-device varia- bility was confirmed from similar switching properties of 10 random devices of the sample. The morphological study of PVP revealed pre- sence of pinholes which assist the electro-migration of top electrode (TE) ions through PVP layer and HfO x thin film, switching the device to low resistance state (LRS). Depth of these pinholes gets smaller with increasing the PVP concentration which results in lower switching voltages. The electrochemical and joule-heating assisted rupture of CF drives the device back to high resistance state (HRS). The pinholes formed at PVP surface has been exploited to obtain a low voltage and reliable switching operation as it restrains the formation of multiple conductive filaments in the switching layer and hence a low voltage reset process. https://doi.org/10.1016/j.ssi.2018.08.003 Received 26 May 2018; Received in revised form 11 July 2018; Accepted 5 August 2018 ⁎ Corresponding author. E-mail address: sptiwari@iitj.ac.in (S.P. Tiwari). Solid State Ionics 325 (2018) 196–200 0167-2738/ © 2018 Elsevier B.V. All rights reserved. T