| Microwave power film matched load is a basic element of microwave circuit and system and is widely used in wireless communication system such as base station, radar, aerospace. With the development of miniaturized and integrated, high frequency electronic system, microwave loads which can operated at high frequency with high power are in the urgent demand. In this work, the low TCR TaN thin film material was prepared and microwave matched loads were designed and fabricated.Low TCR Ta/TaN and TiN/TaN multilayer films constitute by using the positive temperature coefficient of Ta, TiN thin film and the negative temperature coefficient of TaN thin film. The experiment results show that, for the multilayer structure of(Ta/TaN)2 multilayer films, The resistivity of thin films rose up from 165.2 μΩ·cm to 263.6 μΩ·cm and the TCR of the films decreased from 225 ppm/℃ to-213.54 ppm/℃ when the N2 partial flux increased from 3% to 10%. When the nitrogen flow rate was 4%, the TCR of multilayer films reached 18 ppm/℃, which is very close to zero. However, the resistivity of the multilayer film was only 196.4 μΩ·cm. In order to solve the problem that the resistivity of Ta film was too small to make the less resistivity of Ta/TaN multilayer films, the TiN films with larger resistivity was used to build the TiN/TaN multilayer films. For TiN/TaN multilayer films, with the increase of TaN layer sputtering time from 5min to 17 min, the resistivity of the films increased from 400 μΩ·cm to 260.48 μΩ·cm and the TCR decreased from 960 ppm/℃ to-164 ppm/℃.To design and simulate matched load, the equivalent circuit model of the devices had been established based on the lossy transmission line theory and the matching network had been simulated and optimized by HFSS software. The operating bandwidth of the single resistor film matched load 1 was DC-18 GHz, the power load was 10 W and VSWR was less than 1.3. To overcome the problem that the operating frequency and the power load can not be improved simultaneously, the array type load 2 and 3 were designed. The operating bandwidth of load 2 was DC-20 GHz, the power load was 40 W and VSWR was less than 1.3. The operating bandwidth of load 3 was DC-20 GHz, the power load was 100 W and VSWR was less than 1.3. The power capacity of load 3 was 2.5 times than the power capacity of the load 2. The load 4 was designed to reduce the terminal shorted process for high frequency device. The operating bandwidth of load 4 was 30 GHz-42 GHz, the power load was 80 W and VSWR was less than 1.3. Through the thermal simulation by ePhysics software, all the results showed that the maximum temperature of the surface of devices were less than 125 ppm/℃, reaching the design requirements.RF magnetron sputtering, mask patterning technology and screen printing technology were used to prepare thin film load device. Microwave properties of all the devices were measured by vector network analyzer. The results show that the VSWR of the device 1, the device 2 and the device 3 were below 1.3 with their operating frequency range and the VSWR of the device 4 was below 1.5. After the power test, the maximum surface temperature of all the devices was less than 125 ℃. And temperature distribution of the device 2 was observed by infrared detector. The result of the heat distribution was in good agreement with the simulation result. It showed that the array device achieved the purpose of average distribution of power. |
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