Minato Ando

Millimeter-wave Dielectric Ceramics of Alumina and Forsterite with High Quality factor and Low Dielectric Constant

Millimeter-wave dielectric ceramics have been used like applications for ultrahigh speed wireless LAN because it reduces the resources of electromagnetic wave, and Intelligent Transport System (ITS) because of straight propagation wave. For millimeter-wave, the dielectric ceramics with high quality factor (Q·f), low dielectric constant(e r ), and nearly zero temperature coefficient of resonant frequency (τ f ) are needed. No microwave dielectric ceramics with these three properties exist except Ba(Mg 1/3 Ta 2/3 )O₃ (BMT), which has a little high τ f . In this paper, alumina (Al₂O₃) and forsterite (Mg₂SiO₄), candidates for millimeter-wave applications, were studied with an objective to get high Q·f and early zero τ f . For alumina ceramics, Q·f more than 680,000 GHz was obtained but it was difficult to obtain nearly zero τ f . On the other hand, for forsterite ceramics, Q·f was achieved from 10,000 GHz of commercial forsterite to 240,000 GHz of highly purified MgO and SiO₂ raw materials, and τ f was reduced a few by adding TiO₂ with high positive τ f .

Quality Factor of Forsterite for Ultrahigh Frequency Dielectrics Depending on Synthesis Process

Forsterite is a candidate ultrahigh frequency dielectric for wireless communications. The quality factor Q of forsterite (Mg2SiO4) for microwave dielectrics is affected by calcination conditions. The shape of calcined powder particles remains the same as that of fine grains of raw silica materials. This is one of the key points for high Q, because of the realization of a high green density. From the observation of the section of calcined grains by definition (EPMA), it was clarified that Si ions remain in the core part of the grains. The remaining silica affected Q by forming a glassy phase and enstatite (MgSiO3).

Synthesis of High-Quality Forsterite

To establish a process that produces high-quality forsterite stably, calcining and sintering conditions were investigated chiefly and two kinds of silica with different forms, and grain sizes were used as starting raw materials. On the basis of the quality factor (Qf) for forsterite, the sintered samples prepared using powders calcined for 10–24 h, were found to be more stable than those in the case of 2–4 h, and in the case of 24 h of calcination, the samples showed a single phase of forsterite with fine grains. Silica with an amorphous form and a small grain size of 0.25 µm brought a higher Qf value and a wider permissible temperature range of sintering than silica with a crystalline form and a coarse grain size of 0.82 µm. Concerning the sintering temperature, the sample sintered above 1400 °C showed a high Qf value. The Qf value of the sample calcined at 1175 °C for 24 h and sintered at 1450 °C for 2 h using fine-grain amorphous silica of 0.25 µm size, was improved to 219,200 GHz.

Synthesis of Forsterite with High Q and Near Zero TC f for Microwave/Millimeterwave Dielectrics

With the advent of ubiquitous age, the high quality dielectric materials have been required for the wireless communications available to the millimeter-wave as well as microwave frequencies. The utilizable region for the frequency has been expanding to the millimeter-wave region because of the shortage of radio frequency (RF) resources. These high frequencies would be expected for ultra high speed LAN, ETS and car anti-collision system on the intelligent transport system (ITS) and so on. Silicates are good candidates for microwave/millimeterwave dielectrics, because of their low dielectric constant e r and high quality factor (High Q). Forsterite (Mg₂SiO₄) is one of the silicates with low e r of 6.8 and Qㆍf of 240000 ㎓. In this paper, we reviewed following three categories for synthesis of forsterite: (1) Synthesis of high Qㆍforsterite (2) Adjust the temperature coefficient of resonant frequency TC f (3) Diffusion of SiO₄- and Mg-ions on the formation of forsterite

Research & Developments for Millimeter-Wave Dielectric Forsterite with Low Dielectric Constant, High Q, and Zero Temperature Coefficient of Resonant Frequency

Forsterite Mg2SiO4 is a candidate for millimeter-wave dielectrics because of its high Q and low dielectric constant er. Commercial forsterite has been improved with a high Q of 240,000 GHz using high-purity and fine raw materials, and the temperature coefficient of resonant frequency (TCf) can also be adjusted to near-zero ppm/°C by adding 24 wt % rutile compared with that in a previous study. In this study, the TCf, TCe, and er of forsterite ceramics with rutile added are studied for the tuning conditions. Zero ppm/°C TCf of the forsterite with 30 and 25 wt % rutile added was achieved at 1200 °C for 2.5 and 2.25 h, respectively. The er values of the near-zero TCf forsterite with 30 and 25 wt % rutile added are 11.3 and 10.2, respectively.

Low-temperature sintering of silica–boric acid-doped willemite and microwave dielectric properties

Millimeter-wave wireless communications in a high-level information society have been expanding in terms of high-density data transfer and radar for pre-crash safety systems. For these communications, millimeter-wave dielectrics have been expected for the development of substrates with high quality factor (Qf), low dielectric constant (er), and near-zero temperature coefficient of resonance frequency (TCf). We have been studying several silicates such as forsterite, willemite, diopside, wollastonite, and cordierite/indialite glass ceramics. In this study, the synthesis of willemite and low-temperature-sintered willemite for low temperature co-fired ceramics (LTCC) is examined. The raw materials used for preparing slurries in doctor blade tape casting are also analyzed.