.5 Mhz Monolithic Langasite Crystal Filters

The higher performances of the electronic devices for many modern electronic applications are required to improve the performance of the system. For the filters, smaller size, larger bandwidth and higher stability are required. Since the conventional quartz crystal filter can not meet these requirements, new piezoelectric materials with higher electromechanical coupling coefficients and better temperature characteristics have to be found. In recent years, LGS crystal has been found to have the above mentioned features and can replace the quartz crystal in many important applications to meet the requirements for the system.The coupling coefficient of LGS crystals is between that of quartz and lithium tantalate, which is suitable to make filter with the relative bandwidth from 0.3% to 0.8%. Moreover, the rotated Y-cut LGS on the orientation angle of -3o has zero temperature coefficients of frequency. In this study, we studied the monolithic LGS filter innovatively. The main objects of the studies are as follows:(1) The relationship between the temperature-frequency characteristics and the cut angle of Y-cut LGS has been studied to find a rotated Y-cut LGS crystal with zero temperature coefficient of frequency and lager coupling coefficient.(2) The parameter design method of the wafer size, electrode size, electrode thickness and electrode space of one section LGS crystal filter has been studied. Then the design of the three-section cascaded monolithic LGS filter has been studied.(3) The process of LGS monolithic filters has been studied.(4) The reliable design method of LGS monolithic filter has been studied.The high performance LGS monolithic filters has been developed. The filter is characterized by the center frequency of 5MHz, the 3dB bandwidth of 20KHz, the ripple in pass band of less than 0.5dB, the stop band rejection of greater than 80dB, the shape factor (B75/B3) of less than 3, the insertion loss of less than 3dB, the terminating impedance of 1200 ohm, the total volume of 32 mm×12 mm×8 mm, and its operation temperature range of -55℃to +125℃. As our research presents, the LGS crystal is available for implementing filters with larger bandwidth, better thermal stabilities and smaller size.