Improvement of CBRAM Resistance Window by Scaling Down Electrode Size in Pure-GeTe Film

Abstract

TaN-pure-GeTe-Cu bipolar switching devices which can be adaptable to semiconductor processes were fabricated as a function of top-electrode sizes (0.2, 0.4, 10, and 50 μm). The on/off resistance change ratio increased highly with decreasing electrode size. In particular, the on/off resistance change ratio was about 10 3 when the electrode size was scaled down to 200 nm. We obtained the characteristics of conductive bridging memory cell using pure-GeTe film without any doping of Cu or Ag; we also determined the reason for the enhancement of the on/off resistance change ratio when scaling down the electrode size.Index Terms-Conductive bridging random access memory (CBRAM), Cu, dry process, e-beam lithography, GeTe, on/off ratio, scaling down, TaN. I N THE continuing development of universal memory, the search for new memory technologies that can compete with embedded dynamic random access memory and Flash memory has resulted in an emphasis on devices that offer the advantages of low-power nonvolatile operation, nondestructive read, low fabrication cost, and complementary-metal-oxidesemiconductor (CMOS) compatibility [1]. Among the various new memories, conductive bridging random access memory (CBRAM) technology combines key features of the established Flash, SRAM, and DRAM memory platforms, including small size, nonvolatility, high write endurance, and fast random access speed [2], [3]. Because the switching characteristics of CBRAM originate in the formation and annihilation of metallic bridges [4], the metal which takes part in the metallic bridges must show the reversible change between the oxidation and reduction state with applied bias voltage. The metallic material that satisfies both criteria is either Ag or Cu, and thus, a CBRAM-applicable material always contains either one of those two elements. However, these elements are of limited applicability to Si-based semiconductor processes, owing to contamination or difficulty in the dry etching process.

Electrochemical metallization memories—fundamentals, applications, prospects

“…The key piece of evidence normally cited is that the resistance of the ON-state does not depend, or depends only weakly, on the area of the device. This is illustrated in figure 8 for Ag/Ge x Se y /W, and has been reported for a variety of other material combinations, including Cu/Cu 2 S/Pt [35], Cu/Ta 2 O 5 /Pt [36], Cu/Ge x Se y /W [37], Cu/GeTe/TaN [38], and Ag/Zn x Cd 1−x S/Pt [39].…”

“…Ag Cu Ge x S y W: [9,87,14,49,88,48,44,95,16] W: [87] Ge x Se y W: [9,49,72,50,15,43] W : [ 87] Pt: [51] Ni: [49,45,94,96] Ge-Te TiW: [90] T a N : [ 38 investigated than CE materials, as seen in table 1. The choice of Ag as the AE in the early ECM cells [10][11][12] was motivated by the use of As x S y as the electrolyte layer with observed high Ag + mobility.…”

Device and materials requirements for neuromorphic computing

“…The first CBRAM-like switching device was proposed by Hirose et al [83] in 1976 where switching occurred using a Ag dendrite in a Ag doped As 2 S 3 film in a Ag/As 2 S 3 /Mo structure. Germanium (Ge) based chalcogenide materials (GeSe x [84], GeS 2 [85], GeTe [86]) have been widely studied as CBRAM active switching material where Cu and Ag ions show high mobility in the chalcogenide materials. The basic mechanism of switching in CBRAM involves electrochemical reaction at the active anode metal (Ag or Cu) which allows metal to form cations.…”

Realization of forming-free Ag/ZrO2-based threshold selector with high selectivity by optimizing film thickness and scaling down electrode size

“…This is consistent with the previous report that ECM resistance window can be improved by scaling down electrode size. 24 Specifically, the OFF-state resistance is about 200 GΩ when the electrode size is 300 nm. However, the threshold voltage changes slightly with decreasing the electrode size.…”