Elsevier

Microelectronics Reliability

Volume 55, Issues 9–10, August–September 2015, Pages 1320-1322
Microelectronics Reliability

Reliability modeling and analysis of flicker noise for pore structure in amorphous chalcogenide-based phase-change memory devices

https://doi.org/10.1016/j.microrel.2015.06.114Get rights and content

Highlights

  • Analysis of methodology for reset current reduction of PCM in view of reliability

  • Flicker noise induces read disturbance in the device operation resulting in degradation.

  • The trade-off between reducing reset current and improving reliability

  • Reducing contact area degrades PCM device reliability.

  • Device structure design influences PCM device reliability.

Abstract

Phase-change memory (PCM) devices are one of the most promising memory devices to replace the flash memory devices in terms of both scalability and performances. However, typically high programming current to operate devices is a fatal problem in comparison with flash memory. Therefore, many studies have been investigated by changing the contact area and optimizing the structure. In addition, in perspective of characteristic of reliability, the drift and noise are the important problem to degrade the characteristic of devices and the flicker noise is one of the crucial factors in amorphous chalcogenide-based PCM devices. In this paper, we examined the pore-like structure, which is one of the promising structures having small reset current, comparing with conventional mushroom structure by the device reliability analysis for flicker noise using TCAD modeling and simulation.

Introduction

As the scaling of flash memory is progressed to the limit, many alternative memories have been emerging recently. Phase-change memory (PCM) is also one of the strong candidates to replace the flash memory in terms of both scalability and performances because it distinguishes the set/reset states by the phase of chalcogenide material [1], [2]. However, PCM has the problems which typically are high programming current and device reliability [3]. Therefore, the effort to reduce the set/reset current of the device has been actively investigated by changing the composition of Ge–Sb–Te (GST) material, contact area and structure of device [1], [2]. The reason why the structure is important in reducing the set/reset current is that the principle of program/erase operation of PCM is joule heating of GST material. Thus, PCM is very sensitive to the device structure which determines the flow of the heat in the GST. However, reliability is also one of the most important characteristic of memory. In PCM, the drift and noise are the main problems to degrade the device reliability characteristic [4], [5], [6].

In this paper, we analyze the pore structure PCM device which makes the programming current small in the view of reliability characteristic enhancement. Flicker noise affects the operation and reliability of device significantly because the noise induces error at the readout operation, which generates read disturbance of the device. Here, the flicker noise is used as a diagnostic tool of reliability by extracting from the device using TCAD simulation based on Hooge's law [7]. As a result, we provide the correlation between the reset current and reliability for the pore structure of the PCM device.

Section snippets

Modeling and simulations

We analyze the reliability characteristic for two different structures extracting the flicker noise at the read condition (Vread = 0.4 V) using Silvaco 2D ATLAS simulation [8]. The prepared structures are pore structure and mushroom structure which are general structures as shown in Fig. 1. We deposit the TiN to a bottom electrode and top electrode, deposit W to a heater, and deposit amorphous GST according to each structure with Si3N4 insulating layer. The contact area between heater and GST is

Results and discussion

The methods to reduce the reset current are changing the composition of GST, controlling the contact area and varying the structure of device [1], [2]. Here, we analyze the reliability of device in the read situation when the contact area is reduced and the structure is changed from the mushroom to the pore structure.

The pore structure of PCM is known to be effective for the reduction of reset current by confining the switching volume of GST [11]. It reduces the reset current of device by half

Conclusion

In this paper, we analyzed the effect of the method reducing the reset current of PCM in the aspect of device reliability. We investigated two methods by controlling the contact area and varying the device structure. It was found that the trade-off effect between reset current and reliability was observed. The method reducing contact area was beneficial to reset current reduction but the device reliability was degraded since the increased thermal resistance caused the current reduction and the

Acknowledgment

This research was supported by the Sk Hynix [no. 2014-11-0230]. Also, this work was partially supported by the Institute of BioMed IT, Energy IT and Smart IT Technology (BEST) [no. 2014-11-1320], a Brain Korea 21 plus program, Yonsei University.

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