Capacitive evaluation circuits

Most capacitive evaluation circuits do not achieve the maximum possible resolution but are limited by the electromechanical interface, shortcomings in the electronic circuits, or stray signals coupling into the detector and corrupting the output. Section 6.1.2 below illustrates approaches to maximize the sensitivity of capacitive sensor interfaces, potential error sources, and approaches to minimize them. Electronic circuit options are discussed in Section 6.1.3. 

After each iteration, to evaluate the test results, the test-outcome droplets are routed serially from pseudo-sinks to a capacitive-sensing circuit coimected to the electrode for the sink reservoir. The capacitive-sensing circuit can produce a pulse sequence corresponding to the detection of multiple test droplets. 

After the test-outcome droplets are read serially, the capacitive-sensing circuit generates a pulse sequence corresponding to the detection of these droplets. An additional evaluation step is required to analyze these pulse sequences to determine whether the microfluidic array under test has a defect. For example, if a row/column of an array is faulty, there is no generated pulse in... 

To evaluate the magnitude of capacitive currents in an electrochemical experiment, one can consider the equivalent circuit of an electrochemical cell. As illustrated in Figure 24, in a simple description this is composed by a capacitor of capacitance C, representing the electrode/solution double layer, placed in series with a resistance R, representing the solution resistance. 

Noting these uncertainties, we have evaluated the equivalent circuit and present the results in Fig. 3. The potential dependence of the three capacitive elements is shown in Figs. 

With respect to the equivalent circuit in Figure 3.3, an evaluation of the known methods for hysteresis measurements will be given, in view of the effective parasitic capacitance and the influence of reflection. Well known methods to record the hysteresis loop of ferroelectric capacitors by measuring the current response are Sawyer Tower, Virtual Ground, and Shunt measurement as shown in Figure 3.4. 

It should be remembered that the curves shown in Fig. 13L are all simulated and therefore "ideal" in the sense that they follow exactly the equations derived for the given equivalent circuit. In practice, the points are always scattered as a result of experimental error. Also, the frequency range over which reliable data can be collected does not necessarily correspond to the time constant which one wishes to measure. For the case shown in Fig. 13L(a) the semicircle can be constructed from measurements in the range of 1 > o) > 20. In Fig. 13N(b) one would have to use data in the range of about 10 > to 200 to evaluate the numerical values of the circuit elements. From the Bode magnitude plots, can be evaluated from high-frequency measurements (to 100), while R can be obtained from low frequency data (to < 1). The capacitance can be obtained approximately as = l/co Z at the inflection point (which coincides with the maximum on the Bode angle plot), but this would be correct only if (p - 90 that is, if the... 

In the treatment which follows, we assume that discharge of the doublelayer capacitance drives the reaction, and therefore use C = in Eq. (41). The effects of changes in coverage of the adsorbed intermediate are then taken into account by combining Eq. (41) with the kinetic equations for steps in the mechanism. In this method, no assumptions need then be made about the equivalent circuit or the nature of the pseudocapacitance, and the transient current during potential decay is not assumed to be equal to the steady-state current. The results then enable all three definitions of [Eqs. (46)-(48)] to be evaluated and compared, as illustrated in Fig. 10. 

Graphical methods provide a first step toward interpretation and evaluation of impedance data. An outline of graphical methods is presented in Chapter 16 for simple reactive and blocking circuits. The same concepts are applied here for systems that are more typical of practical applications. The graphical techniques presented in this chapter do not depend on any specific model. The approaches, therefore, can provide a qualitative interpretation. Surprisingly, even in the absence of specific models, values of such physically meaningful parameters as the double-layer capacitance can be obtained from high- or low-frequency asymptotes. 

The simplified equivalent circuit in Figure 8b was used to evaluate surface-bound membranes on Si02, TiOa, and ITO electrodes. Figures 10 and 11 present the capacitance curves for n-Si-Si02 and TiOa electrodes with and without OTS- and rhodopsin-containing lipid membranes in KCl buffer. As with the PtO electrodes, the capacitance decreases upon formation of an OTS layer and the membrane on the oxide surface. Table II lists the... 

The effects of the pattern density on CMP characteristics using 8-inch SKWl wafers from SKW Associates, which were specially designed for the characterization of pattern dependencies in ILD CMP, were investigated. The removal rates for various pattern densities and uniformities were evaluated and analyzed after CMP. The experimental result shows that the removal rate decreases linearly as the pattern density increases and these different removal rates for pattern densities cause bad WIDNU. It shows that a dummy pattern must be employed to minimize pattern density variation. However, the introduction of a dummy pattern may increase circuit capacitance, thus it is important to minimize the addition of dummy patterns. Therefore, to limit the removal rates across a die within reasonable values, we must determine what range of the pattern density is available in the die at the target residual thickness. Using a simple model that can take pattern density into consideration, the remaining oxide thickness was calculated and compared with the experimental data. 

The frequency-response behavior, specific capacitance, and ESR can also be evaluated by the EIS method. The EIS experiments are conducted at the open-circuit voltage (OCV) and an alternating potential with a small amplitude (5-10 mV) is... 

---