Silicon nitride insulated

The LAPS represents another major advance in commercially available potentiometric bioanalysis [90]. In this device, a pH-sensitive silicon nitride insulator functions as a phototransistor gate. 

Silicon nitride (Si3N4) is a major industrial material which is produced extensively by CVD for electronic and stmctural applications. It is an excellent electrical insulator and diffusion barrier (to sodium and water vapor) and has replaced CVD oxides in many semiconductor... 

Insulator (dielectrics) Alumina Silicon oxide Silicon nitride Glass Bound to nucleus 1012 to 1022... 

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... 

Thin films of electrical insulators are essential elements in the design and fabrication of electronic components. The most widely used insulator materials (dielectrics) are silicon oxide (Si02) and silicon nitride (Si3N4). These materials are extensively produced by CVD. 

Silicon nitride (Si3N4) is an excellent electrical insulator, which is increasingly replacing Si02 because it is a more effective diffusion barrier, especially for sodium and water which are maj or sources of corrosion and instability in microelectronic devices. As a result, it can perform... 

The design of the Pd-membrane reactor was based on the chip design of reactor [R 10]. The membrane is a composite of three layers, silicon nitride, silicon oxide and palladium. The first two layers are perforated and function as structural support for the latter. They serve also for electrical insulation of the Pd film from the integrated temperature-sensing and heater element. The latter is needed to set the temperature as one parameter that determines the hydrogen flow. 

The most common a-Si H TFT structure is the so-called inverted staggered transistor structure [40], in which silicon nitride is used as the gate insulator. A schematic cross section is shown in Figure 74. The structure comprises an a-Si H channel, a gate dielectric (SiN.v), and source, drain, and gate contacts. 

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. 

The main goal of another microhotplate design was the replacement of all CMOS-metal elements within the heated area by materials featuring a better temperature stability. This was accomplished by introducing a novel polysilicon heater layout and a Pt temperature sensor (Sect. 4.3). The Pt-elements had to be passivated for protection and electrical insulation, so that a local deposition of a silicon-nitride passivation through a mask was performed. This silicon-nitride layer also can be varied in its thickness and with regard to its stress characteristics (compressive or tensile). This hotplate allowed for reaching operation temperatures up to 500 °C and it showed a thermal resistance of 7.6 °C/mW. 

Progress in the design and fabrication of high-quality optical microresonators is closely related to the development of novel optical materials and technologies. The key material systems used for microresonator fabrication include silica, silica on silicon, silicon, silicon on insulator, silicon nitride and oxynitride, polymers, semiconductors such as GaAs, InP, GalnAsP, GaN, etc, and crystalline materials such as lithium niobate and calcium fluoride. Table 2 smnmarises the optical characteristics of these materials (see Eldada, 2000, 2001 Hillmer, 2003 Poulsen, 2003 for more detail). 

Insulator sputtering is similar to the process described for metal sputtering. The only difference is that the source target is a dielectric film. There is less control of the chemical nature and quality of the film as compared to a CVD deposited film. Common sputtered films include silicon nitride and silicon oxide. 

Current interest in saturated Si-N rings stems primarily from the industrial uses of silicon nitride (and related materials), which is a hard, chemically resistant insulator, and as precursors to silicon-nitrogen polymers (poly-silazanes). The formation and precursor chemistry of these polymers are discussed in Section 10.3.3. 

Figure 15-29 Operation of a chemicalsensing field effect transistor. The transistor is coated with an insulating Si02 layer and a second layer of Si3N4 (silicon nitride), which is impervious to ions and improves electrical stability. The circuit at the lower left adjusts the potential difference between the reference electrode and the source in response to changes in the analyte solution such that a constant drain-source current is maintained.

Modern ceramic materials now include zirconium oxide (Zr02), titanium carbide (TiC), and silicon nitride (SiN). There are now many more uses of these new ceramic materials. For example, vehicle components such as ceramic bearings do not need lubrication - even at high speeds. In space technology, ceramic tiles protected the Space Shuttle from intense heat during its re-entry into the Earth s atmosphere. In the power supply industry, they are used as insulators due to the fact that they do not conduct electricity (Figure 3.39). 

Silicon nitride is prized for its hardness (9 out of 10 on the Mohr scale), its wear resistance, and its mechanical strength at elevated temperatures. It melts and dissociates into the elements at 1,900 °C, and has a maximum use temperature near 1,800 °C in the absence of oxygen and near 1,500 °C under oxidizing conditions.41 It also has a relatively low density (3.185 g/cm3). Unlike silicon carbide, silicon nitride is an electrical insulator. The bulk material has a relatively good stability to aggressive chemicals. This combination of properties underlies its uses in internal combustion engines and jet engines. 

In addition, flame propagation is not possible in stainless-steel channels owing to the high heat conductivity and affinity to radicals. But even for materials which do not adsorb radicals, a minimum channel width exists below which no homogeneous combustion is possible any longer. Insulating materials such as silicon nitride and inert layers such as alumina are required to maintain the homogeneous reaction. 

Polymers are a viable material option for the fabrication of highly efficient low-temperature heat exchangers, designed to withdraw the last portion of energy out of the fuel processor off-gases before releasing them to the environment For small-scale MEMS-like systems, the materials commonly applied in this field are silicon [20, 71] (as a material with high heat conductivity) and silicon nitride [71] (as an insulation material). 

Silicon nitride is used in the manufacturing of high-temperature thermal insulation for heat engines and turbines. It is produced by the following reaction. 

Infrared rays which are incident to regions 25 penetrate into the silicon nitride layer and ZnS layer are thereby partly attenuated and reflected, and are finally reflected from the metal layer. The incident rays and the reflected rays cause a complex interference with each other, and an apparent overall reflectance of the light shield layer is reduced if proper thickness and refraction index are chosen for each layer of the insulation layer. Preferable, the refractive index of the first layer 8 is less than the refractive index of the second layer 9. 

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