Oxidation microfabrication

M. Graf, A. Gurlo, N. Blrsan, U. Weimar, and A. Hierlemann. Microfabricated gas sensor systems with sensitive nanocrystalline metal-oxide films , Jom-nal of Nanoparticle Research (2006), 8, 823-839. 

Insulin Oxidation of tyrosine residues at pre-treated (+1.7V, 30s) microfabricated SPCEs Potentiometric stripping analysis (2 min accumulation at -0.2V) Stripping current of 3 pA 0-600 nM 20nM Wang et al. [76]... 

This chapter presents an overview of these composites with a variety of material combinations, as well as their architectures. The major objectives of this chapter are the following (a) to briefly discuss the history and main concepts of FMs in section 1.2 (b) to address the experimental ways to prepare these composites, including coextrusion, microfabrication by coextrusion, and hybrid extrusion and dip-coating, in section 1.3 (c) to demonstrate the various types of FMs in the form of oxide-based or nonoxide-based composites, as well as their various architectures in section 1.4 ... 

Wang, J. Rivas, G. Ozsoz, M. Grant, D.H. Cai, X. Parrado, C. Microfabricated electrochemical sensor for the detection of radiation-induced DNA damage. Anal. Chem. 1997, 69, 1457-1460. Steenken, S. Jovanovic, S.V. How easily oxidizable is DNA One-electron oxidation potentials of adenosine and guanosine radicals in aqueous solution. J. Am. Chem. Soc. 1997, 119, 617-618. 

Cao et al., 2006 recently used microfabricated reactors with online GC for a Raman investigation of silver catalysts during methanol oxidation catalysis. Their results are consistent with those described above. 

The chemical component of CMP slurry creates porous unstable oxides or soluble surface complexes. The slurries are designed to have additives that initiate the above reactions. The mechanical component of the process removes the above-formed films by abrasion. In most planarization systems the mechanical component is the rate-limiting step. As soon as the formed porous film is removed, a new one is formed and planarization proceeds. Therefore, the removal rate is directly proportional to the applied pressure. To achieve practical copper removal rates, pressures greater than 3 psi are often required. These pressures should not create delamination, material deformation, or cracking on dense or relatively dense dielectrics used in silicon microfabrication on conventional dielectrics. However, the introduction of porous ultra-low-fc (low dielectric constant) materials will require a low downpressure (< 1 psi) polishing to maintain the structural integrity of the device [7-9]. It is expected that dielectrics with k value less than 2.4 will require a planarization process of 1 psi downpressure or less when they are introduced to production. It is expected that this process requirement will become even more important for the 45-nm technology node [10]. 

A new alternative to solve this problem is atomic force microscopy (AFM) which is an emerging surface characterization tool in a wide variety of materials science fields. The method is relatively easy and offers a subnanometer or atomic resolution with little sample preparation required. The basic principle involved is to utilize a cantilever with a spring constant weaker than the equivalent spring between atoms. This way the sharp tip of the cantilever, which is microfabricated from silicon, silicon oxide or silicon nitride using photolithography, mechanically scans over a sample surface to image its topography. Typical lateral dimensions of the cantilever are on the order of 100 pm and the thickness on the order of 1 pm. Cantilever deflections on the order of 0.01 nm can be measured in modem atomic force microscopes. 

In this entry, we focus on the discussion of the platform technology for electrochemical sensors, metal oxide semiconductive (MOS) sensors, and piezoelectric based quartz crystal microbalance (QCM) sensors. There are other types of chemical sensors, such as optical sensors, Schottky diode based sensors, calorimetric sensors, field-effect transistor (FET) based sensors, surface acoustic wave sensors, etc. Information of these specific sensors can be found elsewhere and in current journals on sensor technologies. Because of the increasing importance of microfabricated sensors, a brief discussion of microsensors is also given. 

As in all microfabrication processes, the cleanliness of the substrate is very critical for the silicon oxidation process. As discussed above, the crystalline orientation will influence the oxidation rate of silicon dioxide. There are other operational parameters that will affect the oxidation rate of silicon. This includes the dopants in silicon, the trace amount of water, the concentration of Cl-bearing species, the temperature control, and its profile. Extensive assessment of each parameter on the growth rate and the quality of the Si02 layer on silicon can be found in microfabrication related literature elsewhere. ... 

The microfabrication procedure for the TEM membrane windows is shown schematically in Fig. 4.22. A more detailed outline of the procedure is described in [124,125]. The windows are typically fabricated on 3-in. double side polished, n-type Si(lOO) wafers. In the first step, the wafers are cleaned with the two-step standard cleaning procedure used in the semiconductor industry. This procedure ensures the removal of all the organic particles by oxidation, metals by forming soluble complexes, and the native oxide with HF as shown schematically in step 1 of Fig. 4.22 (these steps are hazardous and... 

Microfabrication processes have been used successfully to form micro-fuel cells on silicon wafers. Aspects of the design, materials, and forming of a micro-fabricated methanol fuel cell have been presented. The processes yielded reproducible, controlled structures that performed well for liquid feed, direct methanol/Oj saturated solution (1.4 mW cm ) and direct methanol/H O systems (8 mA cm" ). In addition to optimizing micro-fuel cell operating performance, there are many system-level issues to be considered when developing a complete micro power system. These issues include electro-deposition procedure, catalyst loading, channel depth, oxidants supply, and system integration. The micro-fabrication processes that have... 

---