The mirror-matrix tube: A novel light valve for projection displays

Abstract

A completely sealed-off electron beam-addressed light valve offering high reliability, low thermal impedance, and low-voltage operation is described. It is suitable for projection displays and is capable of producing bright high-contrast images with full gray-scale range and long-term storage. The light valve is contained as the faceplate in an otherwise standard, sealed-off 1½-in diameter vidicon tube and utilizes conventional focusing and deflection components. The target, which is fabricated of refractory materials using high-yield semiconductor-processing techniques, is composed of a dense matrix (500 elements/in) of aluminized silicon-dioxide membranes (~ 3000-Å thickness) which are supported centrally on small silicon posts (4-5 µm high) above a transparent sapphire faceplate. These flat, stress-free oxide membranes can be deflected electrostatically (up to 4°) when addressed with the electron beam. Thus an intensity-modulated display of the deposited charge pattern on the "mirror matrix" is produced when this type of light valve is used in conjunction with reflective schlieren optical arrangement, Mechanical and optical considerations have led to a special 4-leaf geometry of the mirror elements, enabling operation at low-voltage levels (175 V) and a high optical gating efficiency (~ 50 percent) to be achieved. Large-screen (2½-by 3½-ft) displays with up to 35-fL highlight brightness ( ×5 screen gain), 15:1 contrast ratio, and 400 TV lines resolution have been demonstrated. In addition, single-frame displays (1/30-s writetime) with full gray scale storage (of many hours) have been achieved. Preliminary studies using higher density mirror matrices (1000 elements/in) show that the display resolution can be extended to 600 TV lines/picture height.