4kb nonvolatile nanogap memory (NGpM) with 1 ns programming capability

Abstract

A 4k bits nonvolatile high-speed nanogap memory device was fabricated with a newly developed vertical nanogap structure and its memory characteristics were evaluated. The newly developed vertical nanogap structures realized controllable electrode gap and higher yield compared to the initial phase lateral type nanogap structure. The structures were integrated on a CMOS chip. The specially embedded measurement circuit revealed programming speed from a low resistance state to a high resistance state (from on to off state) to be 1 ns.Introduction One of the authors found that thin film metal electrodes with a gap less than 10 nm on an insulating substrate showed nonvolatile memory effect in vacuum [1]. Similar nanogap resistance change were widely observed for metals, such as Au, Pd, Pt, Ta [2], and even for Si [3] and carbon nanotubes [4] not only in vacuum but also in inert gases [10]. The current between the electrodes is due to electron tunneling. And the resistance corresponding to the gap distance was changed and controlled by applying voltage to the electrodes [5]. We have studied this phenomenon and applied for nonvolatile nanogap memory [8], because of its superior properties, i.e. high speed resistance switching, operation in a wide temperature range up to 200 C[1] and intrinsic high bit density. In this paper, results of integration of the nanogap memory (NGpM) on a CMOS LSI structure and evaluation of high speed switching capability using a specially embedded measurement circuit are reported.Fabrication NGpM is initially configured laterally on the insulating substrate as shown in Fig.1a, which is called as lateral type. It has been used to investigate the property and the mechanism of nanogap resistance change [1],[6], [7], however it is not suitable for memory array. We have developed various vertical type nanogap elements and finally adopted a trench type and a hole-in-line type each of which is shown in Fig.1b and 1c respectivly.[8] Using these types of nanogap element, a 4kb NGpM is integrated on a CMOS LSI in which transistors for each nanogap element selection, control circuits and the specially designed embedded measurement circuits were furnished. The technology of the CMOS LSI is 0.35 m high-voltage process of a foundry. Fabrication process on the chip is summarized in table 1. In this vertical type the gap distance between 1st and 2nd metal is determined by the spacer thickness, which is 10nm or less. The device size factor F is 40nm for hole-in-line type and 60nm for trench type. In the vertical type, the nanogap element is located at the cross point of upper and lower electrode, then 4F 2 is minimum size needed for a memory element. A nanogap element finer than 40nm also operates properly.[7] ProgrammingIn our previous work, it was very difficult to investigate the intrinsic programming speed of the nanogap elements, because of limitation of commercially available pulse generators with high-voltage high-speed drivability (10V, 10ns) and also an influence of the parasitic capacitance of lead p...

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Highly stable, extremely high-temperature, nonvolatile memory based on resistance switching in polycrystalline Pt nanogaps

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Metal Nanogap Memory: Performances and Switching Mechanism

“…The as-fabricated Pd, Au, and Pt nanogap memories have 567, 15, and 150 P/E cycles, respectively, measured using the same pulse parameters as mentioned above, as shown in Figures e, S7(a), and S8(a), respectively. We can also find similar features in reported nanogap memory devices, ,,,, which will limit the potential for application in the field of high-speed nonvolatile memory.…”

“…10 A 4K-bit memory array based on vertical nanogap structures has also been achieved through masked deposition and electromigration technology. 25 This suggests that NGM may be a potential candidate for the next generation of ultrahigh-speed nonvolatile memories. The reported shortest SET and RESET pulse widths for nanogap memory are 1 and 200 ns, respectively.…”