A Method of Increasing Storage Capacitance

A Method of Increasing Storage Capacitance

   Disclosed is a method to increase the storage
capacitance of active matrix liquid crystal displays (AMLCDs), by
decreasing the film thickness of the gate insulator only on top of
the gate or Cs (storage capacitance) electrode.  This method makes it
possible to increase the storage capacitance without decreasing the
aperture ratio of the AMLCDs, and also without increasing the
yield-loss caused by the short-circuit defects at the edge of
electrodes.

   Forming the metal-insulator-metal (MIM) structure, inferior
step coverage of the CVD (Chemical Vipor Deposition) insulator
causes electrical breakdown, and brings out short-circuit defects
(see Figure 1).

   This breakdown mainly occurs at the edge of the bottom metal
because of inferior step coverage of the CVD insulator.  Therefore
the breakdown voltage of the MIM does not differ decreasing the film
thickness only on top of the bottom electrode except the edge part of
bottom electrode.

   Figure 2 shows the process flow.  Two insulators are
deposited on the bottom electrode, and the 2nd insulator of only on
top of gate electrode is selective etched.  Using negative
photoresist and backside exposure method, the bias (DL) between the
edge of gate electrode and the edge of the etched hole can be
decreased.  After the deposition of the top electrode, the MIM has
all the same resistance to the electrical breakdown.  Figure 3 shows
the example of an application to the AMLC...