Optimization And Fabrication Of Silicon Integrated Ferroelectric Thin Film Phase Shifters And Arrays At W-band

Phased array radar is the electronic beam scanning radar,widely used in modern military and civil fields.When the electromagnetic wave frequency expands to W-band(75-110 GHz),the phased array radar has the advantages such as high spatial resolution,barrier penetration,and equipment miniaturization,and hence can be widely used in battlefield identification,airport security,anti-terrorism detection,space attack defense and other important areas.With the further development of Moore's law,the phased array radar system based on silicon CMOS technology becomes more and more complicated.The entire RF transceiver system,phased array antenna array,imaging system,and digital control system can be integrated into a single chip so as to constitute a complete SoC system.Tunable phase shifter is a key component in radio frequency applications.In the phased array radar,the phase shifter controls the signal phase of each element antenna,so the cost,power consumption and size of the phase shifter are the key factors that affect the system performance.Ferroelectric material Barium Strontium Titanate(BST)thin films are widely used in phase shifter circuits.The dielectric constant of BST film is associated with DC bias voltage.The phase shifter based on BST films has a lot of advantages such as high power capacity,small volume,low cost,simple structure,easy tuning,low insertion loss,and high phase shift degree,and achieves good dielectric tuning performance in high frequency.In this paper,a W-band silicon phase shifter based on BST thin film and its 1×4 array with on-chip antenna are studied.The specific research contents and innovation points are summarized below:(1)The high frequency characteristic parameters of BST ferroelectric thin films are extracted.Through analyzing the S parameter of coplanar waveguide(CPW)transmission line,a method of extracting the characteristic parameters of BST thin film in high frequency is designed,which is named “three dimensional finite element(3D-FEM)region simulation method”.It is used to extract the dielectric constants of BST thin films growing on high resistivity silicon(hrSi)substrate under the full band(1 GHz-110 GHz)and different DC bias.Compared with the existing methods,the proposed method can overcome the model errors caused by the uneven distribution of spatial electromagnetic fields and the simplified model,while introducing less time cost.(2)Based on the right-handed transmission line phase shifter structure,a righthanded transmission line phase shifter with edge tapering structure is designed,which has the central frequency of 100 GHz,the bandwidth greater than 10 GHz and the insertion loss less than 4dB.Its fabrication and measurement have been completed.By analyzing the distributed capacitance in the circuit,the variable capacitance value that can meet the low insertion loss and the high phase shift degree is obtained,and the number of interdigital electrodes and the gap between interdigital electrodes are optimized.In order to reduce the insertion loss,low loss methods are studied.In this paper,an edge tapering structure is proposed,which effectively reduces the insertion loss.Compared with the existing right-handed transmission linear phase shifter,the proposed phase shifter circuit can be used in W-band and work at 100 GHz.The bandwidth can reach to 10 GHz.(3)A W-band SoC silicon based BST ferroelectric thin film phase shifter and its 1×4 array with microstrip patch antenna is designed by using multilayer micro-nano processing technology.100 GHz on-chip antenna is fabricated on silicon through thin film technology and it has a square patch form.Fed by side feed mode,it can be connected to phase shifter,power divider,filters and other devices in the same plane by using coplanar waveguide,microstrip line and some other planar transmission line type interconnection.The signal feed network uses a quarter-wavelength matching network Tjunction power divider.The simulation results show that the loss within 10 GHz bandwidth is less than 0.5 dB.Phase shifter-antenna 1×4 array is implemented on a silicon chip featuring small size,low cost and good stability.(4)The micro-nano electrode is processed and the phase shifter is tested at W-band.The minimum line width of the metal electrode fabricated on BST/hrSi substrate is 1 um,and the electrode pattern can be obtained by using the lift-off process.In order to test the high frequency characteristics of the phase shifter on the silicon substrate,we configure the vector network analyzer-probe station-spread spectrum module-DC module testing environment,which can realize W-band phase shifter repeatability and accurate on wafer measurement.This is the basic work to verify the performance of on-chip W-band transmission line,phase shifter and array.The design and fabrication of W-band phase shifter based on silicon substrate with ferroelectric thin film is an important basic research of the RF front end of phased array millimeter wave radar.Due to time limitation,the fabrication of phase shifter-antenna 1×4 array is uncompleted,and the subsequent verification test of the array will go on further.