8.1 Extraction of Equivalent Parameters for a Finger Structure

The finger structure is a basic structure used for highly integrated memory cells. This structure consists of a series of top electrodes and a common ground plate. A cross section and the area simulated for the extraction of the basic hysteresis data are sketched in Fig. 8.1.

Figure 8.1: Cross section of a finger structure and the simulated area

Fig. 8.2 shows the simulated $Q/V$ characteristics of this two-dimensional device and compares them to the characteristics of the simple one-dimensional structure of the same width. It already contains properties and effects that exceed the one-dimensional case.

Figure 8.2: 'One-dimensional' capacitor versus finger structure

As a result of the edge effect of the electric field, the field strength in this area will exceed the strength of the coercive field even for small contact voltages. This leads to an area of polarization reversal (Fig. 8.3) and to a decrease of the coercive field of the device.

Of course the two-dimensional analysis is numerically more expensive then the analysis of a simple one-dimensional capacitor.

Figure 8.3: Polarization reversal near the edge of the contact

Figure 8.4: Comparison of the transfer characteristics of a finger structure and the 'one-dimensional' capacitor with fitted hysteresis parameters

With the help of these simulation results it is possible to extract new hysteresis parameters for a one-dimensional device which allow the accurate simulation of this two-dimensional structure. The resulting $Q/V$ characteristics of this calibration are outlined in Fig. 8.4. This feature of the simulator is very useful as it reduces the effort substantially and allows the utilization of a compact model. This opens the door to improved circuit simulation.