Design And Fabrication Of Stress Phase Shifter Based On Silicon Nitride Photonic Chip

In order to solve the problems of high power consumption and slow response rate of the mainstream thermo-optic switch a new kind of stress-optic switch is proposed.The stress optical switch can modulate the light with minimum power consumption and maximum modulation speed without affecting the optical insertion loss.In this paper,a MZI stress optical switch based on silicon nitride photonic chip is designed and fabricated.The finite element simulation software COMSOl is used to simulate the signal arm of the stress phase shifter and the stress optical switch below the changes of stress and effective refractive index in the signal arm under the stress phase shifter are analyzed by changing the size of the stress phase shifter and the strength of the applied electric field.According to the simulation results the length of waveguide and the width of waveguide core the size of MZI stress optical switch stress phase shifter is designed.The whole length of the stress phase shifter is 8000um PZT18 layers the thickness of the film is about 1um and the processing width of the upper electrode is 10um.In the process of fabricating the Stress Phase Shifter the sol-gel method was used to fabricate the Lead zirconate titanate thin film on the silicon nitride photonic chip and the sandwich structure of the PZT thin film was fabricated.In order to avoid the crack of MZI optical switch caused by the stress of PZT thin film during high temperature crystallization the titanium protective layer was constructed by stripping-etching process and the integrity of MZI optical switch was ensured successfully.The stress phase shifter is the key structure of MZI stress optical switch and the PZT film is the driving structure of the stress phase shifter.The performance of PZT film directly determines the optical modulation performance of MZI stress optical switch.Therefore,the transverse piezoelectric coefficient crystal orientation leakage current dielectric and ferroelectric properties of PZT thin films were measured and characterized.In this paper inverse piezoelectric cantilever method is used to measure the transverse piezoelectric coefficient of PZT thin films.Firstly,the finite element simulation software COMSOl is used to simulate the inverse piezoelectric cantilever beam and the relationship between the size of the inverse piezoelectric cantilever beam and the free end displacement of the inverse piezoelectric cantilever beam is determined.According to the simulation results and the processing technology the size of the inverse piezoelectric cantilever beam is designed.The design size is 3mm/3.5mm/4mm the width is 0.6mm the thickness is 0.5mm the height of the base is 0.4mm and the length of the base is 2mm.The inverse piezoelectric cantilever is fabricated on a 2-inch silicon wafer with a thickness of 220μm.Then the transverse piezoelectric coefficient measurement system is constructed by using PCB with inverse piezoelectric cantilever doppler laser vibrometer SDG1022X Function generator and LYC-300B digital lock in amplifier.The transverse piezoelectric constant of PZT thin films e_31,f=7.82pC/N were measured.The piezoelectric constant of PZT thin films d₃₃=10.8pC/N were measured by YE1730 D₃₃meter.The stable 110-directional perovskite（structure）of PZT thin films were determined by X-ray diffractometer（smartarab 9kW）.The PZT thin films were connected by a manual probe platform of MM6150 Keithley the leakage current of PZT thin films was tested by using the Parameter Semiconductor Tester（UB3-07）.The results show that the PZT thin films are still insulated at 30V and the maximum leakage current is 7×10^-9A.The ferroelectric properties of PZT thin films were measured by MULTIFERROIC 100V ferroelectric Tester of American radiant technology company.The hysteresis loop of PZT thin films was saturated the saturation polarization intensity Ps was23μC/cm²the residual polarization intensity Pr was 11.7μC/cm²and the coercive electric field EC was 5.3V.The minim permittivity of PZT thin films is beyond 800 by LCR instrument（ZL-5）.The results show that the PZT thin film of Silicon nitride photonic chip has excellent piezoelectric and ferroelectric properties that is the stress phase shifter can work well in the voltage range of 0-30V and the range of 100hz-10000hz which can meet the needs of silicon nitride photonic chip.