Toward Low-Power Flash Memory: Prospect of Adopting Crystalline Oxide as Charge Trapping Layer

Abstract

Journal of the Electron Devices Society 6 V. CONCLUSION With incumbent flash memory devices operated in the range of 15-17 V, it is imperative to pursue green flash memory that can be operated at voltage less than 10 V to realize a sustainable environment. In this paper, two promising CTL types based on crystalline oxide including crystalline high-k dielectric and crystalline oxide semiconductor which possess the capability to achieve this goal are reviewed. For CTL based on crystalline high-k dielectric, the distinct advantage for memory operation is the k value higher than 30 which is much higher than the amorphous counterpart and beneficial to reduce operation voltage since a higher effective electric field can be exerted on the tunnel SiO2 due to electric flux density continuity. The most concerned retention issue of adopting a crystalline high-k CTL has also be circumvented by passivation of grain boundaries related defects through plasma treatment. The concept of employing crystalline high-k dielectric as CTL not only works for Si-channel flash memory but also Ge-channel memory devices which enable superior memory performance to Si-based counterpart due to higher carrier mobility and more desirable band structure. For CTL based on crystalline oxide semiconductor, a CTL formed by stacking n-type and p-type oxide semiconductor demonstrates typical diode characteristics with a built-in internal electric field. It is the unique internal field that enhances P/E speed while reducing the operation voltage. Both kinds of CTL create a differentiating and pioneering technology that gains an outlook on realizing green flash memory devices.

The conduction process of grain and grain boundary in the semiconductive zirconium oxynitride thin film

“…Figure 1(e) shows the XPS spectrum for the 1000 s etching time and its Gaussian-resolved result. The deconvolution of XPS for Zr 3d electrons indicates that ZrO x N y is composed of oxide compound (I), oxynitride compound (II) and nitride phase (III) [32,[36][37][38]. In accordance with the previous reports, these results confirm that the oxygen has been incorporated into the lattice to form ZrO x N y , which results in the distortion of zirconium nitride lattice.…”

Cubic-phase zirconia nano-island growth using atomic layer deposition and application in low-power charge-trapping nonvolatile-memory devices

“…Thus, the dielectric constant of the nano-islands is expected to be around 35, which is the known dielectric constant of cubic-phase zirconium dioxide [19]. This high-κ value is favorable for the charge-trapping layer of memory devices since it will boost the electric field injection leading to a lower-power memory.…”

“…In addition, high-κ materials are preferred to be used in the charge-trapping layer of memory devices, since this will increase the electric injection field and, therefore, a lower operating voltage can be achieved [18]. ZrO 2 -based dielectrics are a promising candidate for this since they can be crystallized into cubic and tetragonal phases with large dielectric constants (κ-values of ∼35 and ∼46, respectively) [19]. However, it is commonly believed that an amorphous material would be more suitable for a memory charge-trapping layer since grain boundaries existing in crystalline materials can provide leakage paths and deteriorate the retention characteristic of the memory [19].…”

“…ZrO 2 -based dielectrics are a promising candidate for this since they can be crystallized into cubic and tetragonal phases with large dielectric constants (κ-values of ∼35 and ∼46, respectively) [19]. However, it is commonly believed that an amorphous material would be more suitable for a memory charge-trapping layer since grain boundaries existing in crystalline materials can provide leakage paths and deteriorate the retention characteristic of the memory [19]. At the same time, amorphous ZrO 2 has a lower dielectric constant (∼20) than the crystalline phases, which would result in a lower injection field and thus a higher required operating voltage.…”