Passive device, 355 defined

Dielectric Film Deposition. Dielectric films are found in all VLSI circuits to provide insulation between conducting layers, as diffusion and ion implantation (qv) masks, for diffusion from doped oxides, to cap doped films to prevent outdiffusion, and for passivating devices as a measure of protection against external contamination, moisture, and scratches. Properties that define the nature and function of dielectric films are the dielectric constant, the process temperature, and specific fabrication characteristics such as step coverage, gap-filling capabihties, density stress, contamination, thickness uniformity, deposition rate, and moisture resistance (2). Several processes are used to deposit dielectric films including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD) (see Plasma technology). 

The majority of microfluidic methods produce droplet using passive devices generating a uniform, evenly spaced, continuous stream of droplet, whose volume ranges from femtoliters to nanoliters. Their operational modes take advantage of the characteristics of the flow field to deform the interface and promote the natural growth of interfacial instabilities, avoiding in this way the necessity of any local external actuation. Droplet polydispersity, defined as the ratio between the standard deviation of the size distribution and the mean droplet size, can be as small as l%-3%. 

As with many components, monitoring devices can be either passive (typically nonelectronic) or active (mostly electronic). The passive devices often have wide tolerances and thus are useful for preventing abusive conditions that are well outside the expected operating range of the battery. Active devices offer more defined parameter boundaries and often can combine one or more parameters to be monitored. 

The TFTs are made on transparent glass substrates, onto which gate electrodes are patterned. Typically, the gate electrode is made of chromium. This substrate is introduced in a PECVD reactor, in which silane and ammonia are used for plasma deposition of SiN as the gate material. After subsequent deposition of the a-Si H active layer and the heavily doped n-type a-Si H for the contacts, the devices are taken out of the reactor. Cr contacts are evaporated on top of the structure. The transistor channel is then defined by etching away the top metal and n-type a-Si H. Special care must be taken in that the etchant used for the n-type a-Si H also etches the intrinsic a-Si H. Finally the top passivation SiN, is deposited in a separate run. This passivation layer is needed to protect the TFT during additional processing steps. 

The authors have been intimately involved in eondueting research to address many aspects of environmental contaminants for about three decades. Historically, samples of environmental matrices, particularly water and air have been collected at narrow windows of time (i.e., minutes or several hours) which are not representative of the exposure experienced by organisms. Consequently, we initiated the development of what would ultimately be the semipermeable membrane device (SPMD). The SPMD has subsequently proven to be an effective passive sampler for a wide range of hydrophobic contaminants in multiple media. To date, there are more than 180 peer reviewed publications in the open scientific literature, where SPMDs are used for a variety of applications. Some of these publications are critical of the use of passive samplers for certain applications. However, constructive criticism has greatly aided in defining information gaps and limitations of the passive sampling approach. 

Passive sampling can be defined as any sampling technique based on the movement (by diffusion) of analyte molecules from the sampled medium to a receiving phase contained in a sampling device. This mass transfer process is driven by a difference in chemical potentials of the analyte in the two media. This process continues until equilibrium is reached in the system, or until the sampling process is stopped.14 Analytes are retained in a suitable medium within the device, known as a receiving or sorption phase. This can be a solvent, chemical reagent, absorbent, or... 

Besides the advantages that passive sampling may offer, it is important to recognize that in many cases these devices measure a different fraction of contaminants than that defined for the checking of EQS compliance within the WFD. This becomes especially important when monitoring very hydrophobic chemicals (log Kow > 4), where a large fraction of the total amount present in a spot water sample is bound to colloids and particles. In contrast, most passive samplers used for monitoring hydrophobic compounds (e.g., SPMD, Chemcatcher, and silicone materials) measure only the truly dissolved fraction of these chemicals. 

These devices are similar to the microneedle devices produced by microfabrication technology. They include the use of needle-like structures or blades, which disrupt the skin barrier by creating holes and cuts as a result of a defined movement when in contact with the skin. Godshall and Anderson [101] described a method and apparatus for disruption of the epidermis in a reproducible manner. The apparatus consists of a plurality of microprotrusions of a length insufficient for penehation beyond the epidermis. The microprotrusions cut into the outer layers of the skin by movement of the device in a direction parallel to the skin surface. After disruption of the skin, passive (solution, patch, gel, ointment, etc.) or active (iontophoresis, electroporation, etc.) delivery methods can be used. Descriptions of other devices based on a similar mode of action have been described by Godshall [102], Kamen [103], Jang [104] and Lin et al. [105]. 

Some of the problems seen with the commercially available polyimides such as limited shelf life,gelation and high ionic contamination are traceable to the raw materials themselves. A zone refining technique has been perfected for use with organic materials and these precursors have been used to synthesize ultrapure polyamic acids for IC device applications. The key feature of the synthesis is the use of solid ingots of the dianhydrides. Materials prepared by this technique show low metallic impurities and have been shown to be excellent film formers for a variety of applications. In particular a polyimide derived from PMDA-ODA has been used to passivate magnetic bubble devices. IR techniques coupled with electrical measurements have been used to optimize the cure conditions and a simple resist process has been defined to passivate these devices. Device performance compares well with conventional inorganic insulators. 

Materials for use as anisotropically conductive adhesives must satisfy requirements even more stringent than those defined previously for isotropically conductive adhesives. No specifications, however, have been defined specifically for these materials. When used for flip-chip applications, the adhesive not only serves as a physical and electrical interconnection between the device and the substrate, but also serves as the environmental protection and passivation layer. This fact, combined with high adhesive concentrations, makes the ionic contamination levels of these materials more critical than for isotropic conductive adhesives. In addition, the processing of these materials has a greater influence on joint reliability as the anisotropic electrical properties develop only after heat and pressure are applied to the joint. 

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