Microelectronics techniques

So far, there are two types of label-free DNA molecule detection techniques widely studied in laboratories. In the past decades, optical-based label-free detection of DNA molecules gains great development. The sensitivity of the technique has reached the order of pico-mole level. In contrast, although electrochemical method has obtained more and more attentions in the area of detection of DNA molecules because of the effectiveness and costless of the method, the sensitivity of DNA sensors with sihcon electrodes is in the order of p to nano-mole [4], which is low for the propose of detection of ultra-low concentration of DNA molecules, although sensitivity of electrochemistiy based sensors has been greatly improved with the incorporation of microelectronic techniques. 

Thin gold or aluminum wire, with a diameter of 0.025-0.075 mm, is used to make a connection between the bonding pad and the sensor. This wire bonding is performed using standard microelectronic techniques such as thermal compression or ultrasound bonding. The external lead wire is then bonded onto the bonding pad. Because of the thinness of the metallic film of the pad, the external lead wire connection is usually made by thermal compression. Similar to the connection of the thick-film sensor, the conductive epoxy is first applied to the connecting joint and then covered with insulation epoxy or silicone. 

Attempts are still being made to produce improved bolometers operating at or near room temperature. These include vanadium oxide metal-semiconductor transition devices [8.7], bismuth-lead layers [8.8], metallic nickel [8.8a], and aluminium [8.8b], silicon carbide [8.8c], and doped barium titanate ceramic [8.8d] elements. New designs of radiometers and power meters using thermistor bolometers have been described [8.9-11]. Microelectronic techniques have been used to produce fast but sensitive (NEP 10 WHz at 25 MHz and 100 pm wavelengths) uncooled for improved bolometers [8.11a]. 

ISFETs have so far been used primarily in conjunction with conventional macro reference electrodes. This fact greatly limits the potential benefits to be gained from miniaturization of the sensor. An optimal reference electrode for ISFETs should be miniaturizable and display long-term stability, and it should be subject to fabrication with microelectronic techniques. Attempts have been made to miniaturize macro reference electrodes [157], or to use modified surfaces with extremely low surface-site densities as reference FETs [158], but to date the above-mentioned requirements have not been met. 

The miniature form of the Clark sensor depicted in Fig. 7.20 contains an anode and a cathode as well as a small electrolyte stock (chloride solution containing gel-forming agents) behind the membrane. The technology for manufacturing such sensors differs from standard microelectronic techniques. It had to be developed especially for sensor applications (Suzuki 2000). 

The next generation of amperomethc enzyme electrodes may weU be based on immobilization techniques that are compatible with microelectronic mass-production processes and are easy to miniaturize (42). Integration of enzymes and mediators simultaneously should improve the electron-transfer pathway from the active site of the enzyme to the electrode. 

In the microelectronics industry, powdered metals and insulating materials that consist of noimoble metals and oxides are deposited by screen printing in order to form coatings with high resistivities and low temperature coefficients of resistance. This technique may be useful in depositing oxide—metal refractory coatings. 

Burns, R. J. 1994 Reliability Is it Worth the Effort - an assessment of the value of reliability tasks and techniques. Microelectronic Reliability, 34(11), 1795-1805. 

Of these, the most extensive use is to identify adsorbed molecules and molecular intermediates on metal single-crystal surfaces. On these well-defined surfaces, a wealth of information can be gained about adlayers, including the nature of the surface chemical bond, molecular structural determination and geometrical orientation, evidence for surface-site specificity, and lateral (adsorbate-adsorbate) interactions. Adsorption and reaction processes in model studies relevant to heterogeneous catalysis, materials science, electrochemistry, and microelectronics device failure and fabrication have been studied by this technique. 

The growing interest in volatile silyl-metal complexes for chemical vapor deposition reactions should also be mentioned. This technique is extremely useful for the preparation of silicide films in microelectronic devices. Further examples of applications of silicon-metal compounds are given in the appropriate sections. 

The acoustic microscopy s primary application to date has been for failure analysis in the multibillion-dollar microelectronics industry. The technique is especially sensitive to variations in the elastic properties of semiconductor materials, such as air gaps. SAM enables nondestructive internal inspection of plastic integrated-circuit (IC) packages, and, more recently, it has provided a tool for characterizing packaging processes such as die attachment and encapsulation. Even as ICs continue to shrink, their die size becomes larger because of added functionality in fact, devices measuring as much as 1 cm across are now common. And as die sizes increase, cracks and delaminations become more likely at the various interfaces. 

TOF-SIMS can be applied to identify a variety of molecular fragments, originating from various molecular surface contaminations. It also can be used to determine metal trace concentrations at the surface. The use of an additional high current sputter ion source allows the fast erosion of the sample. By continuously probing the surface composition at the actual crater bottom by the analytical primary ion beam, multi element depth profiles in well defined surface areas can be determined. TOF-SIMS has become an indispensable analytical technique in modem microelectronics, in particular for elemental and molecular surface mapping and for multielement shallow depth profiling. 

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