Reflective display using calibration data for electrostatically maintaining parallel relationship of adjustable-depth cavity component

A method for controlling a movable plate of an interferometric modulator to compensate for imbalance conditions that can otherwise cause the movable plate to tilt and not be substantially parallel to a top fixed plate, where a distance between the movable plate and the top fixed plate defines a depth of a modulation cavity in which light is modulated, comprising the steps of:

• (a) providing a first plurality of electrodes distributed over a surface in the interferometric modulator;
• (b) providing at least one other electrode, wherein each electrode of the first plurality of electrodes is disposed opposite the at least one other electrode;
• and
• (c) applying voltage to the first plurality of electrodes and the at least one other electrode, where the voltage applied to each of the plurality of electrodes is selected to produce an electrostatic attraction that compensates for the imbalance conditions and causes the movable plate to move relative to the top fixed plate so as to change a depth of the modulation cavity and a color of light reflected by the interferometric modulator, while preventing the movable plate from tilting out of a generally parallel relationship with the top fixed plate.

An interferometric modulator for reflecting light of a desired waveband, comprising:

• (a) a partially reflective top plate on which light from an external source is incident, a portion of the light incident on the partially reflective top plate being transmitted through the partially reflective top plate and a remaining portion of the light incident on the partially reflective top plate being reflected by the partially reflective top plate;
• (b) a movable partially reflective plate that is suspended and supported by at least one spring beam, so that the movable partially reflective plate is able to move relative to the partially reflective top plate;
• (c) a first set of electrodes disposed on a surface within the interferometric modulator;
• (d) at least one other electrode disposed opposite the first set of electrodes;
• and
• (e) a controlled voltage source that is coupled to the first set of electrodes and to the at least one other electrode, the controlled voltage source applying voltages to each electrode of the first set of electrodes, the voltage applied being at levels selected to:
• (i) electrostatically actuate the movable partially reflective plate to move relative to the partially reflective top plate to define a cavity between the partially reflective top plate and the movable partially reflective plate, so that the cavity has a depth appropriate to modulate light transmitted into the cavity through the partially reflective top plate, whereby the light modulated by the cavity interferes with the light reflected from the partially reflective top plate and achieves the desired waveband of light reflected by the interferometric modulator;
• and
• (ii) compensate any tilt of the movable partially reflective plate relative to the partially reflective top plate so as to keep the movable partially reflective plate substantially parallel with the partially reflective top plate.

A method for compensating for forces acting to tilt a movable partially reflective plate of an interferometric modulator, so that the movable partially reflective plate remains substantially parallel to an adjacent fixed partially reflective plate when a cavity is defined between the fixed partially reflective plate and the movable partially reflective plate to modulate light so that a desired color of light is reflected by the interferometric modulator, comprising the steps of:

• (a) providing a first set of electrodes disposed on a surface within the interferometric modulator;
• (b) providing at least one electrode on at least one other surface opposite the surface on which the first set of electrodes is disposed;
• (c) applying voltage to the first set of electrodes, wherein the voltage applied to each electrode in the first set of electrodes is controlled to:
• (i) actuate the movable partially reflective plate to move relative to the fixed partially reflective plate, so as to define a cavity between the fixed partially reflective plate and the movable partially reflective plate having a depth appropriate to modulate light that is transmitted into the cavity through the fixed partially reflective plate, the light modulated by the cavity interfering with light reflected from the fixed partially reflective plate to achieve a desired waveband of light reflected by the interferometric modulator;
• and
• (ii) compensate any tilt of the movable partially reflective plate relative to the fixed partially reflective plate so as to keep the movable partially reflective plate substantially parallel with the fixed partially reflective plate.