Ta capacitors

Figure 1.51 (a) Ta capacitors as surface mounted devices (SMD) (b) corresponding schemes (c) SEM of sponge-like anode after oxide formation (d) SEM with cross-section through aTa/Ta205 particle. 

Current Development Trends for Ta Capacitors and Research Issues Involved... 

FIGURE 37.8 Schematic diagram of the structure of a solid electrolyte Ta capacitor. 

What are their advantages, and drawbacks if any, as compared, respectively, to conventional liquid electrolyte A1 capacitors and standard-cathode Ta capacitors ... 

Figure 4.8. Current voltage curves for selected A1PO capacitor structures. A high-quality thermally oxidized Si02 dielectric in an identical structure is included for reference. Top contacts are 0.011-cm2 A1 dots thermally evaporated via shadow mask. Bottom contact is made via conductive substrate p++ Si in the case of 600 °C A1PO and Si02 capacitors, and sputtered Ta metal for 300 °C A1PO devices.

Main uses of the metal. Applications of Ta in medicine (in prosthetic implants) are also well known because of its lack of toxicity and excellent compatibility with tissue. It is used for producing capacitors. Tantalum carbide is used in cutting tools. 

Tab. 10.2 Improvement in statistical measures of quality for Ta-AI-O-N compared to Ta-O, Ta-AI-O and Ta-O-N (750 capacitors in each experiment).

Fig. 8.13 A capacitive impedance sensor. Schematic diagram (a) and equivalent electrical circuit (b) 1-vapor absorbing layer 2-Cr/Ni/Au plate of the capacitor (Cl) 3-Ta plate (C2) 4-top, porous metal plate 5 insulating substrate...

There are several things that need to be pointed out on this design. First, the upper electrode is porous, either because it is very thin (10-20 nm) or because it is deposited under such conditions that it cracks. In any case, the polymer beneath it comes into contact with the gas or vapor. Obviously, it is difficult to make robust electrical connections to the top electrode. Fortunately, it is not necessary because it forms an electrically floating plate, which is common to the two capacitors one between the Cr, Ni, Au plate (Ci) and the other between the top and the Ta plate (C2). The corresponding leakage resistances are R and R2. The response of this sensor to water vapor is shown in Fig. 8.14. 

For a lithium beam slowed down to 10 m/s and cooled down close to the Doppler limit (Av/v 0.1), a capacitor 0.5 m long and for ta = Tmax, then ta = 23.5 ms and Tmin=76.5 ms. With the parameters already mentioned one could measure a charge qn as small as the existing limit on the neutron charge qn in about 16 seconds. 

Capacitors can be polarized or non-polarized, depending on the - dielectric. Non-polarized devices have dielectrics consisting of ceramics or polymers (such as polystyrene, polyester, or polypropylene). They are normally box-shaped and their capacity is usually in the range from pF to pF, the maximum voltage up to 1000 V. Polarized capacitors are electrochemical devices the dielectric is an anodic oxide of A1 (pF to 100 mF, potentials up to 1000 V), Ta (capacities pF to 100 pF, potentials up to 20 V), or Nb (- electrolytic capacitor) or a double layer (- supercapacitor, capacities up to some 10 F and potentials up to 2.5 V or 5 V). Aluminum electrolytic capacitors are normally of cylindrical shape with radial or axial leads. Tantalum capacitors are of spherical shape and super capacitors form flat cylinders. 

Before the metal-organic CVD (MOCVD) process of the BST film is discussed, the reasons for using the CVD process, despite its difficulties should be described. The storage node size of the capacitors in the current state-of-the-art DRAMs is about 0.15 x 0.35 x 1.0 pm with minimum spacing of about 0.15 pm between the nodes when the dielectric layer is a SiO/SijN bi-layer or Ta O, and the electrode materials are poly-Si. Here 1 pm is the height of the nodes. Even smaller lateral dimensions are expected when DRAMs use a BST thin film as the capacitor dielectric layer. Even though the BST films have a much smaller t value, which... 

TiCl has been extensively used for the deposition of TiN thin films as the top electrode for Ta O dielectric capacitors as well as for barriers layers in A1 or Cu metalization because it has sufficient vapor pressure and is non-viscous liquid at room temperature. However, thermal decomposition of this precursor and elimination of Cl contamination in the film usually requires high deposition temperatures (> 600°C). As discussed later, the BST CVD process requires a low deposition temperature, less than roughly 450°C, due to issues of process integration and conformal deposition which render the, TiCl useless for this case. We need a metal-organic precursor. 

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