HIGH Q COMPONENTS AND FILTERS

Murata holds a very strong position in the manufacture of high-Q components and filters through the development of novel ceramic materials and devices. Its success is based largely on the ability to develop unique designs of ceramics materials, employ a low-cost manufacturing process, and design useful devices incorporating these materials better and cheaper than probably anyone else. Murata's technology policy leads to the integration of material, processing, design and production processes. This approach is followed in all component and element design. About 10 billion capacitors are produced per month. Murata has extensive tools for design and analysis and has developed its own manufacturing equipment. Material characterization is performed via resonator measurements using HP equipment. Murata's method will become an IC standard next year.

Most of the high-Q components and filters are based on the company's ceramic material formulations combining high dielectric constant with high Q (low dielectric loss), and good thermal stability in both dielectric constant and temperature coefficient of expansion. Murata ceramics are known as the best in the world. Dielectric constants range from 20 to 13,000. A value of 3000 is most popular. Ceramic dielectric constants are notoriously temperature sensitive, but one material changed only 10 percent from -45 to +85

Filters are developed via use of piezoelectric materials (PZT) and multilayer technology for very low frequency applications from the 400 kHz region up to 10 MHz. In addition, ferrite materials are used to develop transformers and noise suppression filters. Pyroelectricity is a material property explored for sensor development. Furthermore, semiconductor materials are used for the development of thermistors. The kind of device used for filtering depends inter alia on frequency and power levels. Thus SAW filters are good at lower power levels and better at the lower frequencies. Piezoelectric filters have been used up to 450 kHz with an unloaded Q of 400 and only about 1/2 mm on the side.

Murata has a good capability to design microwave combline and stepped-impedance filters and duplexers to specified performance. These dielectric filters are constructed in a neat miniaturized monoblock construction out of a block of high-dielectric-constant material (under the trade name GIGAFIL). Murata has written its own proprietary CAD programs to aid in various designs. It has demonstrated progress in miniaturization by showing successive versions of two 900 MHz GIGAFIL duplexers: the mobile version came down from 66 cc in volume and 154 g in mass in 1983 to 3.9 cc and 20 g, respectively, in 1996. The handheld version went from 9.5 cc and 30 g in 1986 to 0.9 cc and 3 g in 1995 (and 0.5 cc in 1997). Murata's work on both dielectric block filters and on multilayer functional substrates is particularly impressive, both leading to miniaturized high-performance components. The latter starts out with thin strips of green ceramic piled in layers. One such device consisted of 21 layers; as many as 600 layers have been contemplated, but not made. The fabrication steps are briefly stated as follows: Mix materials, de-air, make sheets, cut sheets, punch via holes, fill via holes, add dielectric material + solvent + binder, print inner electrode, punch cavity, stack, press, form grooves (for later breaking into separate modules), cofire, inspect, plate Au/Ni electrode, print solder paste, mount components, solder, break where grooved, package and mark, inspect, pack and ship. Filter technology goes to 2 micron thickness, which is expected to be reduced further to reach the 1 GHz mark. The transverse dimension may be as high as a few millimeters.

A major trend in filter technology is the constant push toward three-dimensional (3D) micro-miniaturization, as evidenced here by the multilayer construction currently attempted in filter design. The driver is smaller size, lower mass, lower cost, and sometimes better performance (afforded by integration and the avoidance of connectors and connecting 50-ohm cables). Research into better ways to accomplish this miniaturization might have good payoff though this is perhaps several years away.


Published: July 2000; WTEC Hyper-Librarian