Nonvolatile Resistive Switching Devices Based on Nanoscale Metal/Amorphous Silicon/Crystalline Silicon Junctions
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0997-I04-05
Nonvolatile Resistive Switching Devices Based on Nanoscale Metal/Amorphous Silicon/Crystalline Silicon Junctions Sung Hyun Jo, and Wei Lu EECS, University of Michigan, Ann Arbor, MI, 48109 ABSTRACT M/a-Si:H/c-Si based nonvolatile resistive switching devices with active areas down to 50 nm◊50 nm have been fabricated and explored. Close to 100% device yield was achieved without necessity of high voltage forming process. Both rectifying switching and non-rectifying switching were demonstrated in a controllable fashion. The potential for this structure as nanoscale nonvolatile memory devices was investigated in terms of scalability, retention time, endurance and switching speed. The device showed switching speed faster than 5 ns, endurance cycles more than 106 and retention time longer than 150 days without any degradation of stored data. The devices exhibit improved resistance switching ratio when scaled down.
INTRODUCTION Amorphous silicon (a-Si) based volatile and nonvolatile switching devices have been intensively investigated in the past [1-4]. Such devices are fully compatible with CMOS processing technology, employ relatively inexpensive materials and a simple two terminal device structure. However, conventional metal/a-Si/metal (M/a-Si/M) based devices require a high voltage forming process which is not fully controllable and reduces the device yield. It is also not clear whether such devices can stand the destructive forming process as the devices scale down to nanoscale. Here we report studies on a new type of nanoscale a-Si based resistive switching device in which the effect of forming is minimized by using a heavily doped substrate (c-Si) as the bottom contact material while retaining the advantages of amorphous silicon based devices. Two terminal resistive switching devices based on this M/a-Si/c-Si device structure will be ideally suited in the crossbar architecture [5-7] which offer ultra-high density and intrinsic defect tolerance capability. Compared to crossbar structure devices based on molecules [6], the M/aSi/c-Si devices show comparable scalability and significantly better performance. Furthermore, in the on-state, both rectifying and non-rectifying switching behavior can be obtained in our devices in a controlled fashion. This functionality will offer various options for designing memory devices as well as programmable logic devices/circuits based completely on twoterminal devices. Particularly, rectifying property will reduce the crosstalk problem and make the device structure well-suited for memory and logic operations based on the crossbar scheme [5-7]. EXPERIMENT The device consists of top metal electrode which is usually Ag, the active a-Si layer and a heavily doped ( ρ ≤0.005 Ω∑cm) P-type Si substrate for a bottom electrode. The active a-Si layer can be either undoped a-Si:H prepared by plasma enhanced chemical vapor deposition (PECVD) or undoped amorphous poly Si:H layer grown by low pressure chemical vapor deposition
(LPCVD). The a-Si layer was grown on the heavily doped P
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