A Research Of High-flatness BeO Substrate Used In The Monolithic Microwave Circuit

For its characteristics of high thermal conductivity, good dielectric properties and physics-chemistry properties, BeO has been used widely in high-power module,electronic vacuum, nuclear industry. As ceramics, there is lots of holes on the surface of BeO, whose flatness is bad. BeO bad flatness is bad for the thin-film devices and electrode made on the surface of BeO, even their failure. Roughness and holes limit its application in thin-film circuits and devices. though polishing can improve its roughness, there are lots of holes on its surface. Polishing can lead to its rising cost. In order to find out a method of improving its roughness by low cost, the author studied modification of BeO using the modification of Al2O3 as reference.Glaze was designed based on the glaze of Al2O3, in the early by not changing other characteristics of BeO. The glaze was matched with BeO on the thermal conductivity,having the same εr with BeO. The glaze was made by solid-phase method. the slurry used for silk screen printing was made and was printed smoothly on the surface of BeO by silk screen printing.the influence of the sintering schedule to the rough of BeO was studied. BeO ceramic substrate of Modification was prepared, whose sureface is flat and there were not defects, such as holes and particles. The Ra was low to 0.273 nm and P-V is 2.8 nm in the area of 10×10 μm2. Ra was 0.5nm in the area of 20×20 μm2.Ra was 0.62 nm in the area of 100×100 μm2 and 31.68 nm in the area of 2000×2000 μm2. the roughness of BeO ceramic substrate after modification could be low as nanometer, even sub-nanometer.The influence of modification to the dielectric properties, insulation, flexure strength and thermal conductivity was studied. The result indicated that modification had not lead to the change of four characteristics. Modification improved the roughness of the surface of BeO ceramic substrate and didn`t change other characteristics.