Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-03-31
2001-08-07
Parker, Kenneth (Department: 2775)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C257S294000, C438S030000, C438S065000, C438S070000, C216S026000, C430S321000, C349S106000
Reexamination Certificate
active
06271900
ABSTRACT:
FIELD
The present invention relates to the field of image sensors and display devices.
GENERAL BACKGROUND
Microlenses have long been used in imaging devices to focus light on sensors including charge couple device (CCD) sensors and complementary metal oxide semiconductor (CMOS) sensors. The microlenses significantly improve the light sensitivity of the imaging device by collecting light from a large light collecting area and focusing it on a small light sensitive area of the sensor. The ratio of the overall light collecting area of a sensor to the light sensitive area of the sensor is defined to be a fill factor. Typical fill factors in prior art designs are less than 50%.
One prior art method of generating a color image signal is shown in FIG.
1
A. Light from a subject to be imaged comes in as light rays
104
and passes through a set of microlenses
108
,
112
,
116
. The microlenses are formed on a planarization layer
120
. After passing through the planarization layer
120
, the light
104
is filtered by color filters
124
,
128
,
132
which together form a color filter array. Each color filter
124
,
128
,
132
in the color filter array only allows light of a specific color to pass through. A “color” is defined to be light having a specific range of frequencies. Typical color filters
124
,
128
,
132
used in the color filter array are red, green and blue filters (RGB) or cyan, magenta and yellow (CMY) filters. Each microlens and color filter combination corresponds to a sensor
136
,
140
,
144
. Each sensor is a light sensitive device capable of converting the intensity of light striking the sensor
136
,
140
,
144
into an electrical signal. A microlens, color filter, and sensors such as sensors
136
,
140
,
144
correspond to a pixel of an image. The sensors
136
,
140
,
144
are in close proximity to each other, and each sensor receives filtered light from a corresponding color filter
124
,
128
,
132
. By combining the output of the sensors
136
,
140
,
144
, a processor, such as a graphics processor, can determine the approximate intensity and color of light striking the area in the proximity of sensor
136
,
140
,
144
. By creating an array of such sensors (red sensor
160
, blue sensor
164
, green sensor
168
) as shown in
FIG. 1B
, an overall color image can be reconstructed.
The fabrication of separate microlenses, color filters, and image sensors in the structure illustrated in
FIGS. 1A and 1B
has several disadvantages. For example, one disadvantage of the traditional structure is that many process steps are needed to form a first layer
148
including the sensors
136
,
140
,
144
; a second layer
152
including the color filters
124
,
128
,
132
, and a third planarization layer
156
to support microlenses
108
,
112
,
116
.
Another disadvantage of the current structure is that the microlenses
108
,
112
,
116
are separated from the corresponding image sensors
136
,
140
,
144
by the planarization layer
156
and the color filter layer
152
. The separation reduces the light reaching the sensors
136
,
140
,
144
because some light is absorbed passing through the multiple layers
152
,
156
. Furthermore, the separation results in increased crosstalk between pixels. “Crosstalk” results when off axis light strikes a microlens such as microlens
112
at an obtuse angle of incidence. The off-axis light passes through planarization layers
156
and a color filter
128
missing the sensor
140
which corresponds to the color filter
128
and instead striking an adjacent sensor
136
. Alternately, the off-axis light coming in through microlens
112
may pass between filters
124
and
128
and reach adjacent sensor
136
resulting in an erroneous readings from the image sensor
136
.
Additional disadvantages of the currect micro-lens filter combinations include the additional process steps being used to fabricate the multi-level structure of
FIG. 1
, the decreased reliability resulting from separation of layers
148
,
152
,
156
and the increased material costs used to fabricate separate transparent microlenses
108
,
112
,
116
, color filters
124
,
128
,
132
, and associated planarization layer
156
.
A second use of the microlens, color filter layer, structure is in color display devices.
FIG. 2
illustrates an example of using the microlens color filter structure in a thin film transfer (TFT) liquid crystal display device. In
FIG. 2
, light from a backlight or other light source
204
passes through a color filter layer
208
containing color filters
212
,
216
and
220
. The color filters
212
,
216
,
220
are typically different colors allowing only one color of light to pass through each filter. Microlenses
224
,
228
and
232
in microlens layer
236
focuses the light from corresponding color filters
212
,
216
,
220
through a substrate
240
and a liquid crystal display (LCD) layer
244
to a TFT substrate
248
. Each TFT switch
252
,
256
,
260
corresponds to a corresponding color filter
212
,
216
,
220
. By controlling the amount of light passing through each switch
252
,
256
,
260
, the output of each color filter
212
,
216
,
220
can be controlled. Combining the outputs of the color filters and TFT switches generates the output of a pixel of the color display device.
Display devices formed using the described techniques suffer from the previously described disadvantages including (1) difficulty in fabrication; (2) crosstalk between filters and switches caused by the increased separation generated by the microlens layer; and (3) problems with device reliability resulting from adhesion between multiple layers and increased material costs resulting from the necessity for multiple layers.
Thus an improved method for forming microlens and color filter structures is desired.
SUMMARY
The present invention describes a method of forming a color microlens array on a semiconductor substrate. The method involves depositing a colored microlens resist on a semiconductor surface. The colored microlens resist is patterned and then baked to cause flowing of the colored microlens resist resulting in a color microlens with a curved surface.
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Blakely , Sokoloff, Taylor & Zafman LLP
Intel Corporation
Parker Kenneth
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