Coexistence And Conversion Of Unipolar And Bipolar Resistive Switching Properties In LATP Resistive Random Access Memory

Resistive random access memory(RRAM)is a major non-volatile memory that rises to solve a series of problems caused by the continuous reduction in the size of floating gate memories.It has simple structure,good size reduction,large storage density,and low operating voltage.Currently,it has become the research focus on the storage industry and can play a very important role in the information and other fields in the future.This article proposes to a new resistive switching mode,called any-polar switching resistive mode,which means unipolar resistive switching mode and bipolar resistive switching mode can coexist and convert in RRAM devices.Meanwhile,we use the conductive filaments model to discuss the switching mechanism of the any-polar resistive switching properties.The main conclusions are as follows:1.The resistive switching properties of LATP films obtained by sputtering were studied.When the thickness of the LATP film is less than 10 nm,Pt/LATP/Pt devices do not have resistive switching properties.When the thickness of the LATP is higher than 15 nm,Pt/LATP/Pt device begins to exhibit any-polar resistive switching properties.And when the thickness of LATP is 20 nm,Pt/LATP/Pt devices show stable any-polar resistive switching properties,the resistance ratio is higher than 100 between high resistance state and low resistance state after 75 switching cycles,the SET and RESET voltage distributions are concentrated.The conduction mechanism of the device belongs to typical oxygen vacancy conduction.The SET process mainly uses oxygen vacancies to form conductive filaments to make the device in a low resistance state.During the RESET process,the conductive filaments are broken due to large Joule heat,and the device is in a high resistance state.Because a large number of gaps in the LATP film are favorable for the movement and storage of oxygen ions,the oxidation reaction of oxygen ions at the Pt/LATP interfaces caused by the continuous application of different polar voltages is avoided,which makes the devices show a stable any-polar resistive switching property.2.The resistive switching properties of Ag/LATP/Pt devices were studied.When the device was initially in a high resistance state,the test results showed that the device has a very stable bipolar switching resistive property.The device has a forming voltage of 0.91 V.The resistive switching properties were still stable after 100 cycles of testing,and the ON/OFF ratio was higher than 5000.The SET voltage is between 0.25 V?0.47 V,the RESET voltage is about-0.16 V,and the conductive mechanism is a metal conductive filament formed by the redox of the top Ag electrode.When the device was initially in a low resistance state,the test results showed that the device has any-polar resistive switching properties.After 50 cycles of testing,the resistive switching properties of the devices are still stable,the ON/OFF ratio is higher than 100.At this time,the conductive filaments are formed by oxygen vacancies.Due to the uneven film formation of the LATP film obtained by sputtering and the large number of gaps in the film,some positions of the device are in a low-resistance state during the preparation process.At this time,vacant conductive channels have been formed in the film.When the device is applied with different polar voltages at this time,the movement of Ag ions generated in the device is well suppressed by the oxygen vacancies,so when the device exhibits an arbitrary polarity resistance,it is mainly vacancy conduction.3.In order to verify the resistive mechanism of any-polar resistive switching properties proposed in LATP thin films,since Ti metal is oxyphilic,and can be used as an oxygen storage layer,we comparatively studied resistive switching properties Pt/HfO2/Pt,Pt/HfO2/Ti/Pt and Pt/Ti/HfO2/Ti/Pt device.Pt/HfO2/Pt devices mainly exhibit unipolar resistive switching properties,the ON/OFF ratio and cycle number are too small to work.When a 5 nm thick Ti interlayer is introduced between the Pt bottom electrode and HfO2,the device exhibits any-polar resistive switching properties.The device fails during the negative RESET process after 80 cycles,the ON/OFF ratio is only higher than 10,and the negative RESET voltage distribution interval is much higher than the forward RESET voltage distribution,indicating that the introduction of the Ti oxygen storage layer has optimized functions to improve resistive switching properties of the device.When Pt/Ti/HfO2/Ti/Pt devices are prepared using Ti intercalation layer with a thickness of 5 nm,the device exhibits stable any-polar resistive switching properties,the number of cycles is greater than 120,the device ON/OFF ratio is higher than 100,and the SET and RESET voltage distributions are more concentrated.This proves that the introduction of the Ti oxygen storage layer has improved the resistance of the device.Oxygen ions are stored in the Ti intercalation layer in any polarity resistance test,which makes the device exhibit a very stable any-polar resistive switching property.