Investigation On Atomic Layer Deposition Of HfO_xN_y Film And Its Resistive Switching Device

With the development of semiconductor technology,nowadays the dominant traditional Flash memory is going to facing a series of problems such as reliability and charge leakage that are difficult to overcome in the process of scaling down of device.In recent years,resistive random access memory(RRAM)which has gained great attention as it is regarded as one of the most promising candidate in the application of nonvolatile memories.Compared with traditional Flash memory,the RRAM has advantages such as simple structure,high density and low power.On one hand the resistive switching(RS)phenomena have been widely observed for a variety of materials,including transition metal oxides,nitrides,chalcogenides,and amorphous silicon.However,study of the resistive switching property in oxynitrides such as HfOxNy is lacking.Oxynitrides are compatible with CMOS technologies,and have good thermal stability.Thus,it would be meaningful if nonvolatile memory can be realized in HfOxNy films.We prepare RRAM with HfOxNy films grown by atomic layer deposition(ALD),the RS behavior and mechanism have been investigated.The main work of this thesis are as followed:(1)We prepare HfOxNy films at the temperature of 200?,250?,30? and 350? by PEALD,and fabricate related Ag/HfOxNy/Pt RRAM device.In our research we find the HfOxNy films prepared at the temperatures of 200? and 250? are amorphous,and the related RRAM devices have no sign of resistive switching.The HfOxNy films prepared at the temperatures of 300? and 350? are crystallized,and the related RRAM devices behave bipolar RS.The RRAM devices with HfOxNy films prepared at 300? has good resistive switching properties such as high on/off ratio(more than 105)and concentrated distribution of SET and RESET voltage.(2)Ag/HfOxNy/Pt(Ag-device)and Pt/HfOxNy/Pt(Pt-device)have been fabricated with HfOxNy films prepared at 300?.We make a comparison of Ag-device and Pt-device in order to figure out the resistive switching mechanism.In conclusion,according to the I-V properties both devices are bipolar.In the low resistance state both conduction mechanism are Ohmic.A forming voltage?+3.4V is needed for Ag-device,but no forming voltage is needed for Pt-device.The SET voltages of Pt-device range from +4.4V to +5.6V,and the RESET voltages vary from-1.3V to-2.5V.SET and RESET voltages of Pt-device disperse wider than Ag-device.Both cells can keep their resistance state under the temperature of 85 ?,illustrating the non-volatile property.Ag-device have good resistive switching properties after 450 I-V test cycles,but Pt-device becomes permanent low resistance state after only about 40 I-V tests.Resistive switching is dominated by formation and rupture of Ag filaments for the Ag-device,and is governed by formation and annihilation of anion vacancies for the Pt-device.(3)Compared with HfOx single layer,HfOxNy/HfOx bi-layer can be used to control the formation and rupture of Ag filaments,which leads to better resistive switching properties such as more concentrated distribution of SET and RESET voltage and higher on/off ratio.