Cross-point記憶體開關來整合於RRAM中，由於記憶體發展的趨勢是往高密度且低耗能的方向，欲配合Bipolar-RRAM(雙向電阻式記憶體)的製程及操作相容性，此selector/switch需採雙向操作模式，而MIM雙向性特性及結構製程條件，使其能廣泛的應用在Cross-point記憶體結構中。
而本次的研究成果，TiN-TaOx-TiO2-TaOx-TiN結構，只要面積可達10-10cm2以上，電流密度就可達到107 A/cm2以上。TiN-Al2O3-HfO2-Al2O3-TiN結構已可達104以上的access ratio (Von/(1/2) Von)，而TiN-Al2O3-TiO2-Al2O3-TiN的access ratio也可達103以上。在本次研究過程中，TiN-TaOx-TiO2-TaOx-TiN在小面積小偏壓下是以普爾-法蘭克效應、蕭基發射為主的傳輸機制。在TiN-Al2O3-HfO2-Al2O3-TiN結構中，電流有兩段式機制，定義在轉折處為VT，在V<VT時，是以普爾-法蘭克效應為主，而在V>VT時，則包含了普爾-法蘭克效應、蕭基發射及穿隧機制，此結構為熱電子放射機制。而TiN-Al2O3-TiO2-Al2O3-TiN結構亦也有兩段式電流機制，在V>VT或V<VT，皆以普爾-法蘭克效應及穿隧機制為主，在小偏壓下以穿隧機制，而在大偏壓下可能還會加入熱電子放射的機制。而且本此研究的優勢在於無使用到任何貴重金屬如Pt, Au…，且無磁性材料如BaTiO3…，製程整合對於量產與高密度多層堆疊製程整合都是一大優勢。
未來目標則是與RRAM整合以提高功能性及實用性，可成為未來高密度之3D非揮發性記憶體之控制單元。

In order to develop the 1S1R in cross-point structure, the requirements of the selector are high current density and high access ratio to avoid sneak current path effect for multi-stack array. Furthermore, the reliability of the selector in cross-point array was discussed. In this paper, we focus on VBS (Varistor Bi-directional Switch) development.
For TiN-TaOx-TiO2-TaOx-TiN, we have maximum current density 107 A/cm2, the small bias is attributed Poole-Frenkel emission and Schottky emission, respectively. For TiN-Al2O3-HfO2-Al2O3-TiN, we have maximum access ratio (Von/(1/2) Von) ~104, the small bias is attributed Poole-Frenkel emission, and the larger bias is attributed Poole-Frenkel emission, Schottky emission and tunneling, respectively. For TiN-Al2O3-TiO2-Al2O3-TiN, we have maximum access ratio ~103, the small and larger bias are attributed F-N tunneling and Schottky emission, respectively. The bi-selectors without using noble and magnetic materials show the scaling feasibility due to its inert property to SiO2 encapsulation.
Besides, the selector with higher current density and access ratio will be developed in this project. We plan to design high/low/high bandgap to approach the target with high density stack, high capacity, low power consumption, and cost down. The preparing development MIM with spec. for switch device of bi-direction diode, and avoid the MOSFET process. The stackable memory with selector has the advantage of 3D structure, and avoids transistor fabrication process. It has the opportunity to be the leader of the high density stackable memory – stack cross-point NVM.

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