Silicon nitride thermal conductivity

Aluminum nitride is an attractive material for microelectronics substrates due to its high thermal conductivity, good dielectric properties, and thermal expansion coefficient comparable with silicon. The thermal conductivity of approximately 300 W m is measured for pure single crystal of aluminum nitride. 

CVD plays an increasingly important part in the design and processing of advanced electronic conductors and insulators as well as related structures, such as diffusion barriers and high thermal-conductivity substrates (heat-sinks). In these areas, materials such as titanium nitride, silicon nitride, silicon oxide, diamond, and aluminum nitride are of particular importance. These compounds are all produced by CVD. 1 1 PI... 

A cross-sectional schematic of a monolithic gas sensor system featuring a microhotplate is shown in Fig. 2.2. Its fabrication relies on an industrial CMOS-process with subsequent micromachining steps. Diverse thin-film layers, which can be used for electrical insulation and passivation, are available in the CMOS-process. They are denoted dielectric layers and include several silicon-oxide layers such as the thermal field oxide, the contact oxide and the intermetal oxide as well as a silicon-nitride layer that serves as passivation. All these materials exhibit a characteristically low thermal conductivity, so that a membrane, which consists of only the dielectric layers, provides excellent thermal insulation between the bulk-silicon chip and a heated area. The heated area features a resistive heater, a temperature sensor, and the electrodes that contact the deposited sensitive metal oxide. An additional temperature sensor is integrated close to the circuitry on the bulk chip to monitor the overall chip temperature. The membrane is released by etching away the silicon underneath the dielectric layers. Depending on the micromachining procedure, it is possible to leave a silicon island underneath the heated area. Such an island can serve as a heat spreader and also mechanically stabihzes the membrane. The fabrication process will be explained in more detail in Chap 4. 

Russell, L.M., Donaldson, K.Y., Hasselman, D.P.H., Corbin, N.D. Petrovic, J.J. and Rhodes, J.F. Effect of vapor-liquid-solid and vapor-solid silicon carbide whiskers on the effective thermal diffusivity/conductivity of silicon nitride matrix composites , J. Am. Ceram. Soc., 74[4] (1991) 874-877. 

The next three chapters review the deposition of thermally-induced dielectric films (Chapter 3) and metallic conducting films (Chapter 4), as well as plasma-enhanced films of either type (Chapter 5). The many chemical systems employed to create these films are considered, and the nature of the resulting films is presented. Films studied are silicon dioxide, silicon nitride, polysilicon, epitaxial silicon, the refractory metal silicides, tungsten and aluminum. 

Silicon carbide, widely employed as an abrasive (carborundum), is finding increasing use as a refractory. It has a better thermal conductivity at high temperatures than any other ceramic and is very resistant to abrasion and corrosion especially when bonded with silicon nitride. Hot-pressed, self-bonded SiC may be suitable as a container for the fuel elements in high-temperature gas-cooled reactors and also for the structural parts of the reactors. Boron carbide, which is even harder than silicon carbide, is now readily available commercially because of its value as a radiation shield, and is being increasingly used as an abrasive. 

Nonoxide ceramics, such as silicon carbides, silicon nitrides, and boron nitrides, have unique mechanical and functional characteristics. Silicon carbides with high thermal conductivity, high thermal stability, excellent mechanical strength, and chemical inertness are especially considered as effective catalyst supports. 

Combat . [Caiborandum] Bortwi nitride powds. exhibiting high thermal conduct. and high dielec, str. used as additives to sflicone and qx>xy resins, flu-(winated hydrocarbons, silicone oils, etc. 

The extraordinary mechanical, thermal and electrical properties of carbon nanotubes (CNT) have prompted intense research into a wide range of applications in structural materials, electronics, and chemical processing.Attempts have been made to develop advanced engineering materials with improved or novel properties through the incorporation of carbon nanotubes in selected matrices (polymers, metals and ceramics). But the use of carbon nanotubes to reinforce ceramic composites has not been very successful. So far, only modest improvements of properties were reported in CNTs reinforced silicon carbide and silicon nitride matrix composites, while a noticeable increase of the fracture toughness and of electrical conductivity has been achieved in CNTs reinforced alumina matrix composites. ... 

K. Hirao, K. Watari, M. E. Brito, M. Toriyama, S. Kanzaki. Fligh Thermal Conductivity in Silicon Nitride with Anisotropic Microstructure. J. Am. Ceram. Soc., 79.2485-88 (1996). 

Key words aluminum nitride, silicon carbide, sinterability, thermal conductivity, microwave attenuation... 

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