Research On Integrated Transceiver Chip Based On VCSEL And PIN

With the information industry develops rapidly,and optical interconnection as a key technology in the information communication network architecture of science and technology,develops rapidly in line with the requirements of the times.At present,the optical interconnection module is still based on discrete receiver and transmitter,which can be packaged separately.In recent years,many researchers have been exploring the monolithic chip integration scheme of laser and detector,but there are many researches on the horizontal integration of laser and detector based on the vertical cavity surface emission,and few studies on the vertical integration and simultaneous operation of two devices.In this project,we study the integrated transceiver chip pair of duplex communication.One terminal transmits optical signal of 805nm wavelength and receives optical signal of 850nm wavelength,and the other one transmits optical signal of 850nm wavelength and receives optical signal of 805nm wavelength.In this paper,the structure of the integrated transceiver chip based on the vertical integration of the VCSEL and PIN-PD is discussed in detail,which can satisfy the simultaneous operation of the two devices in the coaxial direction,and can effectively improve the coupling efficiency between the chip and the fiber.Furthermore,the integrate structure introduced in this paper can realize single fiber bidirectional optical communication,which can not only improve the integration level of optical interconnection modules,but also reduce the complexity and cost.The main contents of this paper are as follows:1.The theoretical basis of VCSEL and PIN is described.The basic theory of VCSEL structure and its performance parameters are introduced,such as threshold current,slope efficiency and 3dB bandwidth.The working principle and characteristics of quantum well laser are described in detail,and the special design that needs to be satisfied by VCSEL unit is introduced in detail in combination with the integrate structure studied in this subject,namely the design of aperiodic DBR is adopted in VCSEL,which can make the reflectivity of the terminal to be larger than 99%at 805nm and less than 10%at 850nm.For PIN unit,mainly discusses its basic structure,working principle and working performance.2.The structure design of integrated chip based on VCSEL and PIN is introduced in detail.In this part,firstly the design process of VCSEL unit is introduced,and expounds in detail the theoretical analysis process of the optimal design of the wet oxidation current confinement window structure with a diameter of 6um under the active region of 4 pairs quantum well.Secondly,the wavelength division multiplexing(WDM)is applied to transmit and receive optical signals at 805nm and 850nm,so as to solve the problem of optical decoupling between the two parts of the integrated device.And design isolation between transceiving channels is greater than 40dB.Finally,Al2O3 material is used as the electrical isolation layer to solve the problem of electrical decoupling of two parts of the device.When the isolation degree of the transceiving channel is set to-40dB,the bandwidth is 8GHz.The VCSEL's threshold current is 1.0mA,slope effiency is 0.695W/A,maximum output power is 8mW,3dB bandwidth is 15GHz.The quantum efficiency of PIN unit is up to 80%and 3dB bandwidth is 21 GHz.3.The key steps of the process of fabricating the integrated chip are explored.For the etching protection of integrated chip,the thick adhesive lithography technology based on AZ5214 and polymid materials was studied,and the clear lithography pattern of 6um was realized.PECVD deposition process of highy homogeneous SiO2 dieletric film was studied for the production of passivation layer of integrated chip,and the dielectric film of 0.5um was realized.The wet oxidation process was studied for making the current confinment window of VCSEL unit,and the oxidation depth of 3um under the condition of ensuring the complete structure of epitaxial wafer layer was realized.In order to make the electrode on the step with high aspect ratio,this paper studied the reverse-pattern lithography process,and realized a clear ring electrode pattern with a diameter of 3um.4.The fabrication of integrated chip is completed and the feasibility of integrated chip is verified.Based on the transceiving signal of wavelength at 850 nm and receiving signal of wavelength at 805 nm chip structure,the VCSEL device and PIN units were fabricated.and the VCSEL's performance was tested analysed by PIN unit.The VCSEL unit of integrated chip of transceiving signal at 850nm has the threshold current density of 3KA/cm2,maximum output optical power of 40.2 mW,slope efficiency of 0.74 W/A.In this way,the laser characteristics of VCSEL unit with the aperiodic DBR structure of the integrated chip are verified experimentally,and the feasibility of the integrated chip is further verified.Based on the analysis and research of the problems encountered in the fabrication process,the process realization flow and the layout of integrated chip are re-optimized and designed.