Methods for fabricating a multiple modular assembly

Details Methods for fabricating a multiple modular assembly Methods for fabricating a multiple modular assembly

1999-03-16

2001-11-13

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Making device or circuit emissive of nonelectrical signal

C438S106000, C438S023000, C438S024000

Reexamination Certificate

active

06316278

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of fabricating modular assemblies. More particularly, the present invention relates methods for forming displays using multiple flexible layers.
2. Description of Related Art
Fabrication of display panels is well known in the art. Display panels may be comprised of active matrix or passive matrix panels. Active matrix panels and passive matrix panels may be either transmissive or reflective. Transmissive displays include polysilicon thin-film transistor (TFT) displays, and high-resolution polysilicon displays. Reflective displays typically comprise single crystal silicon integrated circuit substrates that have reflective pixels.
Liquid crystals, electroluminescent (EL) materials, organic light emitting diodes (OLEDs), up and downconverting phosphor (U/DCP), electrophoretic (EP) materials, or light emitting diodes (LEDs) may be used in fabricating flat-panel display panels. Each of these is known in the art and is discussed briefly below.
Liquid crystal displays (LCDs) can have an active matrix backplane in which thin-film transistors are co-located with LCD pixels. Flat-panel displays employing LCDs generally include five different components or layers: a White or sequential Red, Green, Blue light source, a first polarizing filter, that is mounted on one side of a circuit panel on which the TFTs are arrayed to form pixels, a filter plate containing at least three primary colors arranged into pixels, and a second polarizing filter. A volume between the circuit panel and the filter plate is filled with a liquid crystal material. This material will rotate the polarized light when an electric field is applied between the circuit panel and a transparent ground electrode affixed to the filter plate or a cover glass. Thus, when a particular pixel of the display is turned on, the liquid crystal material rotates polarized light being transmitted through the material so that it will pass through the second polarizing filter. Some liquid crystal materials, however, require no polarizers. LCDs may also have a passive matrix backplane which is usually two planes of strip electrodes which sandwich the liquid crystal material. However, passive matrices generally provide a lower quality display compared to active matrices. Liquid crystal material includes, but is not limited to, twisted nematic (TN), Super TN, double STN, and ferroelectric. U/DCP and EP displays are formed in a similar fashion except the active medium is different (e.g., upconverting gas, downconverting gas, electrophoretic materials).
EL displays have one or more pixels that are energized by an alternating current (AC) that must be provided to each pixel by row and column interconnects. EL displays generally provide a low brightness output because passive circuitry for exciting pixel phosphors typically operates at a pixel excitation frequency that is low relative to the luminance decay time of the phosphor material. However, an active matrix reduces the interconnect capacitance allowing the use of high frequency AC in order to obtain more efficient electroluminescence in the pixel phosphor. This results in increased brightness in the display.
LED displays are also used in flat-panel displays. LEDs emit light when energized. OLEDs operate like the LEDs except OLEDs use organic material in the formation of the diode.
Regardless of the type of active medium used, displays are generally comprised of at least a substrate and a backplane. The backplane forms the electrical interconnection of the display and comprises electrodes, capacitors, and transistors in at least some embodiments of a backplane.
FIG. 1A
illustrates a rigid display device wherein the active matrix display backplane
10
is coupled to a rigid substrate
12
. Typically, the active matrix display backplane is also rigid.
FIG. 1B
shows another rigid display. There, the active matrix display backplane
10
is coupled to a rigid substrate
12
(e.g., glass). Also shown is a plurality of blocks
14
. These blocks may be fabricated separately and then deposited into holes on substrate
12
by a process known as fluidic self assembly; an example of this process is described in U.S. Pat. No. 5,545,291. These blocks may each contain driver circuitry (e.g., MOSFET and capacitor) for driving a pixel electrode. The active matrix backplane includes transparent pixel electrodes and row/column interconnects (not shown) to electrically interconnect the blocks
14
. The plurality of blocks
14
is coupled to the active matrix display backplane
10
and the rigid substrate
12
.
FIG. 1C
shows a reflective display
16
coupled to a rigid substrate
12
.
FIG. 1D
shows a reflective display
16
coupled to a rigid substrate
12
. A plurality of blocks
14
is coupled to the reflective display
16
and to the rigid substrate
12
.
Placing elements, such as pixel drivers, on a rigid substrate is well known. Prior techniques can be generally divided into two types: deterministic methods or random methods. Deterministic methods, such as pick and place, use a human or robot arm to pick each element and place it into its corresponding location in a different substrate. Pick and place methods generally place devices one at a time and are generally not applicable to very small or numerous elements such as those needed for large arrays, such as an active matrix liquid crystal display.
Random placement techniques are more effective and result in high yields if the elements to be placed have the right shape. U.S. Pat. No. 5,545,291 describes a method that uses random placement. In this method, microstructures are assembled onto a different substrate through fluid transport. This is sometimes referred to as fluidic self-assembly (FSA). Using this technique, various blocks, each containing a functional component, may be fabricated on one substrate and then separated from that substrate and assembled onto a separate rigid substrate through the fluidic self assembly (FSA) process. The blocks which are deposited onto receptor regions of a substrate may include any of a number of different functional components, such as LEDs, pixel drivers, sensors, etc. An example of a particular type of block and its functional component is described in copending U.S. patent application Ser. No. 09/251,220 which was filed Feb. 16,1999 by the inventor John Stephen Smith and which is entitled “Functionally Symmetric Integrated Circuit Die”. This application is hereby incorporated herein by reference.
As noted above,
FIGS. 1B and 1D
illustrate a display substrate
12
with blocks
14
formed in the rigid substrate
12
. These blocks
14
may be deposited through an FSA process. In the FSA process, a slurry containing the blocks
14
is deposited over the rigid substrate
12
and the blocks
14
rest in corresponding openings in the substrate
12
.
FIG. 2
shows a block
14
and a circuit element (not shown) on the top surface
18
of block
14
. Generally, blocks have a trapezoidal cross-section where the top of the block is wider than the bottom of the block.
FIG. 3
shows block
14
in a recessed region of the rigid substrate
12
. Between the block and the rigid substrate is an eutectic layer
13
. The block has a top surface
18
.
FIG. 4
shows a planar side view of a rigid substrate coupled to a rigid display backplane with a plurality of blocks between the display backplane
30
and substrate
12
. The plurality of blocks are functionally part of the display backplane
30
and are deposited onto receptor regions of the substrate
12
. Each block drives at least one transparent pixel electrode. The pixel is fabricated over a transistor which is fabricated in the block.
FIG. 5
shows a portion of an array in an active matrix display backplane. The control line rows
31
and
32
in this device are coupled to gate electrodes along a row and the control line columns
34
and
35
are coupled to data drivers which supply pixel voltages which are applied to the pixel electrodes. A column line
34
is c

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