溶液法制备ZnO纳米微粒薄膜的低压电阻开关特性

Low-voltage resistance switching of solution-processed ZnO nanoparticle films

电阻开关随机存储器是一种有望应用于下一代非易失性存储器的新型存储器件,而ZnO是一种可应用于低电压低能耗电阻开关随机存储器的过渡金属氧化物.我们利用溶液法在40°C低温下制备获得粒径约为7–10 nm的ZnO纳米微粒,然后在优化制备条件下旋涂获得表面平整致密的n型ZnO纳米微粒薄膜.利用紫外-可见光吸收谱推算出ZnO纳米微粒薄膜的光学带隙宽度约为3.34 eV.ITO/ZnO/Al电容器结构的电流-电压曲线具有优良的双极性电阻开关特性:置/复位电压低至±0.2 V;在0.18 V的读取电压下可获得大于100的高/低电阻值比.电场作用下薄膜中ZnO分子发生电化学还原/氧化反应,导致薄膜中富余Zn原子组成的导电细丝周期性导通/截断,从而使得ZnO薄膜表现出电阻开关特性.

Resistive random access memory（ReRAM） has been considered as one of the most promising next-generation nonvolatile memory devices.ZnO is one kind of direct-band-gap semiconductors exhibiting good thermal stability,abundant raw materials for synthesis and low preparation cost.It shows extensive application potential in light-emitting diodes,photocatalysis and perovskite solar cells.Compared to ZnO bulk,nano-sized ZnO exhibits many special characteristics,such as non-toxic,non-migratory,fluorescence,piezoelectricity and conductivity.Moreover,ZnO is also one kind of transition metal oxides exhibiting resistive switching properties.There are many methods to synthesize nano-ZnO,such as chemical vapor deposition,sol-gel method and hydrothermal synthesis method.The common method to synthesize ZnO nanoparticles is the solution method using methanol as the reaction solvent.This method needs to heat methanol to 80°C,while the boiling point of methanol is only 64.7°C.Thus,this method is not safe.In this paper,ZnO nanoparticles were prepared by solution method using ethanol as the reaction solvent,which make the reaction temperature decrease to 40°C.Then,ZnO nanoparticles were dissolved in anhydrous ethanol to prepare a smooth,transparent and dense ZnO nanoparticle film by means of spin-coating under optimized preparation conditions.X-ray diffraction spectrum and scanning electron microscope image demonstrate polycrystalline ZnO nanoparticles with an average particle size of 7–10 nm were obtained.Ultraviolet-visible absorption spectra reveal the optical band gap of the n-type ZnO nanoparticle film is about 3.34 eV.Current-voltage curves of the ITO/ZnO/Al capacitor structure exhibit excellent bipolar resistive switching characteristics：the Set/Reset voltage is as low as ±0.2 V,and the high/low resistance ratio is more than 100 at the reading voltage of 0.18 V,which is expected to be applied in the next generation of low-power-consumption nonvolatile memory devices.The formation/rupture of conductive Zn-atom filaments due to the electrochemical redox reaction of ZnO molecules induced by the external electric field is responsible for the resistive switching.