The Study Of Multi-physical Field Tunable Multilayer Films Composite And Their Devices

The magnetoelectric(ME)multilayer composite film consists of piezomagnetic phase and piezoelectric phase.The ME effect is obtained from the coupling between ferromagnetic sequence and ferroelectric sequence through the interface stress coupling between the two phases.It can be applied to magnetic field and electric field dual-tunable microwave filters,magnetic sensors,magnetic memory and other fields.Two-dimensional(2D)transition metal chalcogenide semiconductor materials molybdenum disulfide(MoS₂),whose energy band and electronic structure are sensitive to the outside conditions,such as electric,magnetic,optical and stress,show the rich physical properties under the much physical fields coupling.Therefore,the performance of the MoS₂film devices such as field effect transistor,junction transistor and photoelectric detectors,etc,is expanded.In the thesis,the main work and results are as follows.1)YIG/Terfenol-D/PZT multilayer ME composite film was designed,and its ME coefficient was calculated theoretically.The magnetic field modulation and electric field modulation performance of YIG/Terfenol-D/PZT multilayer microstrip line filter are simulated by HFSS.Pt film,Terfenol-D film and PZT film prepared by magnetron sputtering on GGG/YIG substrate,and copper microstrip line transducer prepared by sputtering on sapphire substrate,formed a GGG/YIG/Pt/Terfenol-D/Pt/PZT/Pt multilayer film microwave filter.The thickness,surface morphology and physical properties of each layer of the multilayer composite film were characterized.The microwave frequency characteristics of the filter were tested with the magnetic field modulation and the electric field modulation.The experimental results are similar with the simulation results.The frequency modulation range is 4?10 GHz under the applied bias magnetic field range of800?2800 Oe,with the frequency modulation efficiency 3.07 MHz/Oe.The frequency modulation range is greater than 270 MHz under the applied electric field range of 0?300V/cm,with frequency modulation efficiency of 90 MHz/(k V·cm^-1).The multilayer composite can control the microwave performance under the magnetic field and the electric field,and is applied in microwave filters,phase shifters,resonators and other devices with adjustable frequency.2)The n-type monolayer MoS₂ films were prepared by chemical vapor deposition(CVD)method.It is proposed that large size MoS₂ films can be obtained by adjusting the flow direction of the reaction zone and regulating the concentration and distribution of precursor in the reaction zone.The results of optical microscope,AFM,Raman and PL spectra show that the MoS₂ films obtained by the improved CVD method are large-area monolayer films.The n-type MoS₂ thin films can be effectively doped by nitrogen plasma doping technology to obtain p-type thin films with less damage.The contact characteristics of Cr/Au,Ti/Au,Ni and Pt and monolayer MoS₂ before and after doping were characterized respectively.Among the four kinds of electrodes,the smallest contact resistance of Cr/Au electrode was got with the n-type MoS₂,and the smallest contact resistance of Pt electrode with p-type MoS₂,which is conducive to obtaining good device performance.The magnetic properties of MoS₂ films have been studied,and the n-type MoS₂ films prepared by CVD method,the doped and unannealed MoS₂ films and the doped and annealed MoS₂ films all have ferromagnetism.The ferromagnetism of MoS₂film is derived from sulfur vacancy and the zigzag boundary of molybdenum.The doped and unannealed MoS₂ films are easy to be magnetized along the perpendicular plane direction of the film.This is because the electron spin splitting of the Mo dz² orbital causes the electron spin polarization,thus forming the magnetic moment in the perpendicular plane direction of the film.3)The lateral pn homojunction photodiodes and npn-type BJTs are prepared by nitrogen plasma selective doping technique with mask.The rectification ratio of lateral MoS₂ pn homojunction reaches 10².The amplification factor of BJT reaches 10²,and the amplification can be controlled by the base voltage V_B and the collector voltage V_C.The optoelectronic detection performance of the pn homojunction and a simple circuit with a pn junction and a BJT were tested and their physical mechanism was discussed.The optical responsivity R_?and the external quantum efficiency EQE of the pn photodiode increase with the increase of the absolute value of the bias voltage,which is along with the variation of the photocurrent with the voltage.The normalized detectivity D*increases with the increase of the reverse bias voltage,and increases first and then decreases with the forward bias voltage.When the forward bias voltage is small,the normalized detectivity D*reaches the maximum value.The response time increases with the increase of voltage and the response time is the shortest in the reverse bias voltage.The optimized photoelectric detection parameters are as follows:when the reverse bias voltage is 10 V,the optical responsivity reaches 48.5 A/W,the external quantum efficiency reaches11301%,the detectivity reaches?10⁹ Jones,and the response time reaches 20 ms.The current amplification factor?of BJT is controlled by the voltage applied on pn photodiode,the voltage V_CE between the collector and the emitter of BJT and its back voltage V_g,which is related to the internal structure and carrier transport of the device.It is shown that electric field regulation can effectively control the performance of photoelectric detection and obtain better device performance,which provides a new way for the design and fabrication of high-performance photoelectric detection system.