1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a liquid crystal display having two display surfaces.
2. Description of the Related Art
Owing to their capability to be manufactured in small sizes, minimized thickness, and consume low amounts of power, flat panel display devices such as liquid crystal displays are used in portable computers such as notebook PCs, office automation equipment, and other audio/video devices. Liquid crystal displays control electric fields applied to liquid crystal material having anisotropic dielectric properties and selectively transmit light to display images. Unlike other display devices that are capable of generating light (e.g., electro-luminescence devices (EL), cathode ray tubes (CRT), light emitting diodes (LED), etc.), liquid crystal displays, by themselves typically do not generate light.
Accordingly, liquid crystal displays require external light sources to generate light. Liquid crystal displays can be classified as transmission-type and reflection-type devices, depending on the type of external light source used. Transmission-type liquid crystal displays typically include a backlight unit arranged against a rear transparent substrate. Light generated by the backlight unit is transmitted through the rear transparent substrate and guided through a second transparent substrate to a display surface via liquid crystal material. In reflection-type liquid crystal displays, a reflective surface is typically formed on the rear substrate such that external light is reflected from the reflective surface to the display surface via the liquid crystal material.
Referring to FIG. 1, a liquid crystal display panel used in a transmission-type liquid crystal display device includes an upper substrate 10 and a lower substrate 12. The upper substrate 10 supports components including color filters, a common electrode, a black matrix layer, etc. The lower substrate 12 supports components including signal lines (e.g., data lines and gate lines) and thin film transistors (TFTs) formed at crossings of the gate and data lines. TFTs switch data signals applied to data line to liquid cells in response to a scanning signal (e.g., gate pulse) applied to a gate line. Pixel electrodes are formed at pixel areas arranged between the gate and data lines and a pad area 14, connected to each gate and data line, applies data signals and scanning signals supplied from a driving circuit (not shown) to the gate and data lines, respectively.
Referring to FIG. 2, a TFT fabrication process may be performed as follows. First, gate electrode 20 and corresponding gate lines are formed by depositing metal such as aluminum Al, molybdenum Mo, chrome Cr, etc., on a glass substrate 18 and patterning the deposited metal by photolithography. A gate insulation film 22 is formed by depositing an inorganic film such as silicon nitride SiNx on the glass substrate 18 where the gate electrode 20 is formed. A semiconductor layer 24 of amorphous silicon (a-Si) and an ohmic contact layer 26 of a-Si doped with n+ ions are sequentially formed on the gate insulation film 22. A source electrode 28 and a drain electrode 30 are formed on the ohmic contract layer 26 by depositing a metal such as molybdenum Mo, chrome Cr, etc. The source electrode 28 is subsequently patterned and integrated with a corresponding data line. A portion of the ohmic contact layer 26 exposed within an aperture between the source electrode 28 and the drain electrode 30 is typically removed via a dry or wet etching process. Next, a protective film 32 made of silicon nitride SiNx or silicon oxide SiOx is deposited over the entire surface of the glass substrate 18 so as to cover the TFT. A contact hole is then formed in the protective film 32 and a pixel electrode 34 made of indium tin oxide (ITO) is deposited in the contact hole to electrically connect to the drain electrode 30.
TFTs selectively supply video signals to each of their corresponding liquid crystal cells based on a gate signal applied to their corresponding gate lines. Accordingly, the transmittance of light, within a liquid crystal cell, generated by a backlight may be controlled so that the liquid crystal display can display images.
FIG. 3 illustrates a sectional view of a liquid crystal display having two display surfaces.
Referring to FIG. 3, liquid crystal displays having two display surfaces typically include a first liquid crystal display panel 40 having a first set of two substrates bonded together, a first backlight unit 42 for transmitting light to the first liquid crystal display panel 40, a first liquid crystal display module including a first pad area 44, to which a driver (not shown) is connected for driving liquid crystal cells of the first liquid crystal display panel 40, a second liquid crystal display panel 50 having a second set of two substrates bonded together, a second backlight unit 52 for transmitting light to the second liquid crystal display panel 50, and a second liquid crystal display module including a second pad area 54, to which a driver (not shown) is connected for driving liquid crystal cells of the second liquid crystal display panel 50.
Liquid crystal displays having two display surfaces are capable of displaying first images in a first direction on a first display surface via the first liquid crystal display module and displaying second images in a second direction on a second display surface via the second liquid crystal display module.
Use of liquid crystal display devices such as those illustrated in FIG. 3 is disadvantageous, however, because two liquid crystal display modules are required to display the first and second images on the first and second display surfaces. Accordingly, liquid crystal display devices such as those illustrated in FIG. 3 tend to be undesirably thick.