Thermal expansion coefficients device

Because of the high functional values that polyimides can provide, a small-scale custom synthesis by users or toU producers is often economically viable despite high cost, especially for aerospace and microelectronic appHcations. For the majority of iudustrial appHcations, the yellow color generally associated with polyimides is quite acceptable. However, transparency or low absorbance is an essential requirement iu some appHcations such as multilayer thermal iusulation blankets for satellites and protective coatings for solar cells and other space components (93). For iutedayer dielectric appHcations iu semiconductor devices, polyimides having low and controlled thermal expansion coefficients are required to match those of substrate materials such as metals, ceramics, and semiconductors usediu those devices (94). 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

The crystal quality of the InGaN QWs becomes poor mainly due to the lattice-constant mismatch and the difference of the thermal expansion coefficient between InN and GaN with increasing the In composition [4,5]. Therefore, in order to improve the external quantum efficiency (i/ext) of the InGaN-based LEDs and LDs, it is important to elucidate and optimize the effects of the various growth conditions for the InGaN active layer on the structural and optical properties. Recently, we reported a fabrication of efficient blue LEDs with InGaN/GaN triangular shaped QWs and obtained a substantial improvement of electrical and optical properties of the devices [6,7]. 

Many different substrates are used fora-Si H deposition. Usually Corning 7059 glass [390] and crystalline silicon are used for materials research, as both have similar thermal expansion coefficients to fl-Si H. Devices are mostly made on... 

Composite-based PTC thermistors are potentially more economical. These devices are based on a combination of a conductor in a semicrystalline polymer—for example, carbon black in polyethylene. Other fillers include copper, iron, and silver. Important filler parameters in addition to conductivity include particle size, distribution, morphology, surface energy, oxidation state, and thermal expansion coefficient. Important polymer matrix characteristics in addition to conductivity include the glass transition temperature, Tg, and thermal expansion coefficient. Interfacial effects are extremely important in these materials and can influence the ultimate electrical properties of the composite. 

The principle of their operation is the same, but the method of implementation of the sensor is largely dependent on the conditions of the application. Thus, a zirconia sensor for measurement of 02 in molten steel (1,600°C) has to be designed in such a way that the thermal expansion coefficients of the different layers in this device are matched. On the other hand, a room-temperature potentiometric oxygen sensor can be constructed (Yamazoe et al., 1987) by using another set of materials ... 

Room-temperature embossing on PMMA (Lucite) and copolyester (Vivak) plates was achieved using a Si master. A hydraulic press was employed to apply the pressure (450-2700 psi). Such a room-temperature operation will prevent breakage of the Si master due to the differences in the thermal expansion coefficients of Si and PMMA. This room-temperature procedure improves the lifetime of the master, so that 100, instead of 10, devices per master can be embossed [177], For comparison, when embossing was performed at 140°C in a convection oven using G-clamps to apply the pressure, the Si template could be used to emboss up to 65 PMMA chips [215]. 

In forsterite ceramics the mineral forsterite (Mg2Si04) crystallizes. They have excellent low-dielectric-loss characteristics but a high thermal expansion coefficient which imparts poor thermal shock resistance. During the 1960s they were manufactured for parts of rather specialized high-power devices constructed from titanium and forsterite and for which the operating temperature precluded the use of a glass-metal construction. The close match between the thermal expansion coefficients of titanium and forsterite made this possible. Today alumina-metal constructions have completely replaced those based on titanium-forsterite and the ceramic is now manufactured only to meet the occasional special request. 

With reference to the thermal characteristics of the substrate, and in light of the proposed use of the printed pattern, there may be a need to match the thermal expansion coefficient of the substrate and the dry ink. In addition, for printing of flexible devices, the flexibility of the printed pattern must be adjusted to that of the substrate. 

Certain semiconductor device fabrication methods require the formation of a single-crystal deposit of the semiconductor on an insulating substrate. In epitaxial methods, the semiconductor is deposited on a single-crystal piece of substrate chosen, in part, on the basis of the match of the lattice parameters, thermal expansion coefficients and chemical compatibihty of the substrate and deposit. Singlecrystal substrates include those of AI2O3, MgAl204, Q -quartz andZrSi04. ... 

Therefore the dielectric constant is changed with temperature and the resonant frequency will change with temperature, and the microwave devices cannot respond at a specific frequency if the dielectric materials in microwave frequencies show a large TCK and thermal expansion coefficient a due to the thermal expansion of dielectric materials and the temperature dependence of polarizability. In general, the a of dielectric ceramics, which is well known as the slope of the Cockbain equation, is about 10 ppm/°C. Therefore control of TCP can be achieved by adequate manipulations of TCK. It is an important requirement for practical applications to control the stable TCP, nearly zero, which is available to temperature-stable microwave devices. 

Diamond has a low heat capacity, a low thermal expansion coefficient, and a high mechanical and thermal stability. These properties are very useful for devices using high dynamic thermal stress such as ink-jet heads. Indeed, ink-jet heads were fabricated using diamond films [17, 422]. Figure 13.8 shows a thermal actuator... 

Quartz was used as a filler in the manufacture of optical devices from epoxy in a UV-curable system. Figure 6.22 shows that addition of a filler can substantially reduce curing shrinkage which is highly desirable in the precise manufacture of these materials. Reduced shrinkage is the result of a low thermal expansion coefficient of quartz in comparison with the resin. 

The actual pressure sensor is offered in a package made of resin or metal. When the pressure device is directly bonded to the package, the sensor characteristics are affected by the difference in physical properties such as thermal expansion coefficient and Young s modulus between silicon and the package material. The glass base is used for lessening the effect of the difference. We have learnt, however, that the thermal expansion coefficient of the glass base itself also has a profound effect on the temperature characteristics of the sensor. 

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