CN105514268A - Resistive random access memory with high on-off ratio and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of modification and manufacture of a nonvolatile memory in a CMOS very-large-scale integrated circuit, and specifically relates to a resistive random access memory with high on-off ratio and a preparation method thereof. The resistive random access memory with high on-off ratio sequentially comprises, from top to bottom, a top electrode, a resistive material layer, a bottom electrode, an adhesive layer and a substrate. The resistive material layer is composed of three layers of homojunction metal oxide, and the oxygen vacancy concentration of the intermediate layer of the three-layer homojunction metal oxide structure is greater than that of the other two layers. The substrate is a Si substrate of which the surface is provided with a layer of SiO2 formed through thermal oxidation. According to the invention, by controlling oxygen partial pressure of the three layers of homojunction, the three layers are of different oxygen vacancy concentration, oxygen vacancy is easier to move, a higher on-off ration is achieved, the storage states of different information can be better distinguished, and crosstalk is avoided.

Description

A high switching ratio resistive memory and its preparation method

technical field

The invention relates to a resistive memory (RRAM), in particular to a high switching ratio resistive memory and a preparation method thereof, belonging to the technical field of modification and manufacture of nonvolatile memory (Nonvolatile memory) in CMOS ultra-large-scale integrated circuits (ULSI) .

Background technique

In recent years, with the development of the economy, the market demand for large-capacity, high-density, low-power, low-cost, and portable memory has greatly increased. However, in the process of continuous advancement of semiconductor process nodes, today's representative non-volatile memory Flash encounters unavoidable shortcomings, such as: high operating voltage, slow working speed, and so on. It has been unable to meet the market's requirements for ultra-high storage density of non-volatile memory. Therefore, it is particularly urgent to make a major breakthrough in the field of memory materials and technologies, and to develop a new generation of non-volatile memory technology.

New types of nonvolatile memory include ferroelectric memory (FRAM), magnetic memory (MRAM), phase change memory (PRAM) and resistive change memory (RRAM). Among them, the resistive memory has the advantages of simple device structure (MIM), simple manufacturing process, low operating voltage, fast erasing and writing speed, multi-value storage, and compatibility with today's CMOS technology. One of the top contenders. When an appropriate external voltage is applied to the RRAM, the resistance of the device will switch between a high resistance state and a low resistance state, thereby realizing the storage of '0' and '1' of information. The on/off ratio (R _HRS /R _LRS ) of the device determines the storage capacity of the device, and reflects the degree of distinction between storage states of different information.

At present, many memories do not distinguish the storage states of different information clearly, which leads to the existence of "crosstalk" problem, which seriously affects the accuracy of reading data, which is not conducive to the practical application of resistive variable memory. Therefore, how to solve the problem that the degree of differentiation of the storage states of different information is not high enough is an urgent problem to be solved at present.

The study found that reasonable control of the oxygen partial pressure of the three-layer homojunction metal oxide growth can obtain a high switching ratio resistance switching phenomenon, thereby effectively solving the problem of insufficient discrimination between different information storage states.

WJMa et al. from the State Key Laboratory of Optoelectronic Materials and Technology at Sun Yat-sen University studied Pt/TiO ₂ /BaTiO ₃ /TiO ₂ /Pt resistive memory, and found that in this structure, TiO ₂ acts as a depositor of oxygen vacancies, while BaTiO ₃ acts as an oxygen vacancy supplier, and this three-layer structure has a significant impact on the concentration and distribution of oxygen vacancies. In resistive memory, oxygen vacancies have always played a central role, and adjusting the concentration and distribution of aerobic vacancies can obtain a relatively large on-off ratio, thereby improving the degree of differentiation of the memory for different information storage states. However, their work is mainly concentrated on the basis of heterojunction, the process is complicated, and the obtained IV curve switch ratio is about tens of times.

Contents of the invention

Based on the above problems, the present invention provides a high switching ratio resistive variable memory and its preparation method, by growing the same metal oxide resistive switch material film into a three-layer homojunction structure according to different oxygen partial pressures, in order to realize reasonable The movement of oxygen vacancies can be regulated to obtain a high on-off ratio, which makes the degree of discrimination between the storage states of different information higher, and improves the storage capacity of the memory.

Technical scheme of the present invention is as follows:

A resistive variable memory with a high switching ratio, comprising a top electrode, a resistive material layer, a bottom electrode, an adhesive layer, and a substrate from top to bottom, and is characterized in that: the resistive material layer is a three-layer homogeneous junction It is composed of metal oxide, and the concentration of oxygen vacancies in the middle layer of the three-layer homojunction metal oxide structure is greater than that in the two side layers.

The substrate is a Si sheet with a layer of SiO ₂ on the surface thermally oxidized.

The material of the bottom electrode and the top electrode is conductive metal or metal nitride.

The material of the resistive material layer is TiO _x , HfO _x , ZrO _x , NiO _x , ZnO _x , or TaO _x in binary metal oxides.

The top electrode is a circular point electrode with a diameter of 200 μm.

The homojunction metal oxide in the middle layer of the resistive material layer is at least one order of magnitude greater than the oxygen vacancy concentration of the two side layers, and the magnification of each order is 10 times.

The preparation method of the resistive variable memory with high switching ratio comprises the following steps:

Step 1, growing an insulating layer SiO _on a silicon wafer by thermal oxygen to prepare a substrate;

Step 2, sequentially sputtering or evaporating metal Ti and M on the substrate obtained in step 1, wherein Ti is the bonding layer, and M is the bottom electrode;

Step 3: On the bottom electrode M, three layers of homojunction metal oxides with an oxygen vacancy concentration in the middle layer greater than that on both sides are sequentially prepared from bottom to top, that is, the resistive material layer, and then in-situ annealing is performed on it; the preparation method is by The pulsed laser deposition method deposits three layers of resistive materials sequentially in the same cavity by adjusting the partial pressure of oxygen;

Step 4, sputtering or electron beam evaporation on the resistive material layer to prepare the top electrode.

The present invention adopts:

(1) The preparation process is compatible with the CMOS process, and compared with the general RRAM, no new process steps are added, and the operation is simple and easy to implement.

(2) By controlling the growth oxygen partial pressure of the three-layer homojunction, their oxygen vacancy concentrations are different, making the oxygen vacancies easier to move, so as to obtain a higher switching ratio, so that the storage state between different information is better. area to avoid crosstalk.

To sum up, the present invention does not increase the difficulty of the process, but also effectively improves the degree of data differentiation of the memory, and avoids the phenomenon of crosstalk.

Description of drawings

Fig. 1 is a schematic cross-sectional view of the basic structure of the resistive variable memory according to the present invention;

The I-V curve of the resistive variable memory of Fig. 2 of the present invention;

Fig. 3 is a schematic diagram of the distribution of oxygen vacancies in the resistive memory according to the present invention;

Reference signs: top electrode-1, high oxygen partial pressure layer-2, low oxygen partial pressure layer-3, high oxygen partial pressure layer-4, bottom electrode-5, bonding layer Ti-6, SiO ₂ layer-7 , Si layer-8.

specific implementation plan

The present invention will be described in further detail below in conjunction with the accompanying drawings and the preparation of the _TiOx resistive variable memory:

The process of the resistive variable memory with high switching ratio prepared by the present invention is described as follows in conjunction with the accompanying drawings:

1) Prepare the insulating layer. One layer of SiO is grown by thermal oxygen on the silicon wafer ₈ as the insulating layer 7, as shown in Figure 1;

2) Prepare the bottom electrode. On the insulating layer 7, metal Ti and Pt (thickness 200nm) are sequentially sputtered, wherein Ti is used as an adhesive layer, and Pt is used as a bottom electrode;

3) Preparation of resistive thin film. The first layer _4TiOx was prepared by pulsed laser deposition with a thickness of 100nm and an oxygen partial pressure of 10Pa, as shown in Figure 1; followed by the growth of the second layer 3 with a thickness of 300nm and an oxygen partial pressure of 1Pa; finally, the third layer 2 was grown. , with a thickness of 100nm and an oxygen partial pressure of 10Pa;

4) Prepare the top electrode. A circular Au dot electrode with a radius of 200 μm and a thickness of about 200 nm was prepared using vacuum evaporation, as shown in Figure 1.

The present invention directly obtains different oxygen vacancy concentration distributions (high concentration in the middle layer and small layers on both sides) by directly regulating the growing oxygen partial pressure of the three-layer homojunction, so that the oxygen vacancies can move more easily, thereby obtaining a larger on-off ratio, which can Better distinguish the storage status of different information, thereby avoiding the "crosstalk" phenomenon.

Claims (6)

1. A high switching ratio resistive variable memory, comprising top electrode, resistive variable material layer, bottom electrode, adhesive layer and substrate successively from top to bottom, is characterized in that: The resistive material layer is composed of a three-layer homojunction metal oxide, and the oxygen vacancy concentration of the middle layer of the three-layer homojunction metal oxide structure is greater than that of the two side layers; The substrate is a Si sheet with a layer of SiO ₂ on the surface thermally oxidized. 2. The high switching ratio resistive variable memory according to claim 1, characterized in that: the homojunction metal oxide in the middle layer of the resistive material layer is at least an order of magnitude greater than the oxygen vacancy concentration of the layers on both sides, each The magnification of magnitude is 10 times. 3. The high switching ratio RRAM according to claim 1, wherein the material of the bottom electrode and the top electrode is conductive metal or metal nitride. 4. The high switching ratio resistive variable memory according to claim 1, characterized in that: the material of the resistive variable material layer _{is TiOx} , HfOx, _ZrOx , _NiOx , _ZnOx , Or TaO _x . 5. The high switching ratio RRAM according to claim 1, wherein the top electrode is a circular dot electrode with a diameter of 200 μm. 6. The preparation method of high switching ratio RRAM as claimed in claim 1, comprising the following steps: Step 1, growing an insulating layer SiO _on a silicon wafer by thermal oxygen to prepare a substrate; Step 2, sequentially sputtering or evaporating metal Ti and M on the substrate obtained in step 1, wherein Ti is the bonding layer, and M is the bottom electrode; Step 3: On the bottom electrode M, three layers of homojunction metal oxides with an oxygen vacancy concentration in the middle layer greater than that on both sides are sequentially prepared from bottom to top, that is, the resistive material layer, and then in-situ annealing is performed on it; the preparation method is by The pulsed laser deposition method deposits three layers of resistive materials sequentially in the same cavity by adjusting the partial pressure of oxygen; Step 4, sputtering or electron beam evaporation on the resistive material layer to prepare the top electrode.