The majority of electronic cameras marketed today are color cameras. In modern single-photosensor-array color cameras, the photosensor is typically tiled with a repeating pattern of at least three photosensor types, where each type has a different spectral response. Most such photosensor arrays use an array of red, green, and blue filters, where one filter may be positioned over each photosensor of the array to produce the tiling pattern with at least one filter of each type present in each instance of the tiling pattern.
For example, in a typical tiling pattern 100 of a typical photosensor, a red 102, a green 104, and a blue 106 filter are positioned over photosensors of the array. In existing color photosensor arrays, the fourth photosensor may be covered by a filter 108 of any one of red, green, or blue, or left without a filter.
It is also known that high energy ion implants, such as are necessary to create deep diffused regions and deep junctions without extensive drive-in steps, can cause damage to crystal lattice structure. Damaged crystal structure is undesirable because it can cause leakage and mismatches between adjacent photosensors.
A color photosensor array comprising photosensors of a first type having a thick overlying silicon layer, photosensors of a second type having a thin overlying silicon layer, and photosensors of a third type having no overlying silicon layer; the photosensors of the first type having peak sensitivity in the red, the photosensors of the second type having peak sensitivity in the green.
In a photosensor array 150 (
The three distinct types of photosensors are prepared by using photomask-patterned blocking oxides to prevent deposition on photodiodes where expitaxial growth is not wanted, and removing that oxide where expitaxial growth is desired. For example, in a particular embodiment, an oxide is present over the blue 162 absorber region while not present over the absorber regions of red 166 and green 164 photosensors while the first thickness of expitaxial silicon is grown, and present over absorber regions of both the green 164 and blue 162 absorber regions, while epitaxial silicon of thickness equal to the difference between second and first thickness of epitaxial silicon is grown on the red 166 absorber region. In alternative embodiments, other maskable layers may be used to determine presence and absence, and thickness, of epitaxial silicon over the absorber regions.
The three types of photosensors illustrated in
The blue sensor 162 has a spectral response approximating the curve 180 in
The green sensor 164 has a spectral response approximating curve 182 because most blue photons are absorbed in the overlying thin silicon layer 170, while many longer-wavelength red and green photons penetrate filter layer 170 and reach its absorber 154. Some green, and many red, photons penetrate the absorber region without being absorbed, the result is peak sensitivity in the green.
The red sensor 166 has a spectral response approximating curve 184 because not only are blue photons absorbed by the thick silicon layer 172, but so are most of the green photons. This leaves primarily red photons to reach its absorber 154. Some red photons penetrated the absorber without being absorbed and detected. This sensor therefore has a lower sensitivity than the green or blue sensors, but has a peak spectral response in the red.
In a particular embodiment, junction depth of the absorbers 154 is the same for red, green, and blue photosensors.
In a camera system 200 (
In a particular embodiment of color correction circuitry, as illustrated in
In all embodiments, additional layers, such as a transparent oxide layer or other scratch protection and passivation layer, is deposited across the top of all three types of sensors illustrated in
In an alternative embodiment, where light of red wavelengths is not significantly absorbed in filter regions 172 and 170 but is absorbed in absorber region 154 of red sensor 166, and red light is less significantly absorbed than previously discussed in absorber region 154 of green sensor 164, but green light is largely absorbed in absorber region 154 of green sensor 164, subtractors 216, 218 may be omitted from the color processing circuitry illustrated in
It is expected that the RED, GREEN, and BLUE outputs of the color processing circuitry illustrated in
A color photosensor array designated A including photosensors of a first type having a thick overlying silicon filter layer, photosensors of a second type having a thin overlying silicon filter layer, and photosensors of a third type having no overlying silicon layer; the photosensors of the first type having peak sensitivity in the red, the photosensors of the second type having peak sensitivity in the green.
A color photosensor array designated AA including the photosensor array designated A wherein the thick overlying silicon layer and the thin overlying silicon layer are single-crystal silicon layers grown atop an implanted pinning region, an absorber layer of each photosensor underlying the pinning region.
A color photosensor array designated AB including the photosensor array designated A or AA wherein the thick overlying silicon filter layer is approximately 1.2 microns thick.
A color photosensor array designated AC including the photosensor array designated A, AA or AB wherein the thin overlying silicon filter layer is approximately 0.6 microns thick.
A color photosensor array designated AD including the photosensor array designated A, AA, AB or AC further comprising color correction circuitry.
A color photosensor array designated AE including the photosensor array designated AD wherein the color correction circuitry comprises at least two multipliers and at least one subtractor, configured such that a green output is determined by subtracting a multiple of a signal derived from photosensors of the first type from a multiple of a signal derived from photosensors of the second type.
A method designated B of providing a red, a green, and a blue signal representing a color image including providing a color photosensor array comprising photosensors of a first type having a thick overlying silicon filter layer, photosensors of a second type having a thin overlying silicon filter layer, and photosensors of a third type having no overlying silicon layer; the photosensors of the first type having peak sensitivity in the red, the photosensors of the second type having peak sensitivity in the green; focusing light from a scene on the photosensor array as an optical image; and sensing photosensors of the first type to provide the red signal, the second type to provide the green signal, and the third type to provide the blue signal, the red green and blue signals together forming an electronic representation of the optical image.
A method designated BA including the method designated B wherein the thick overlying silicon layer and the thin overlying silicon layer are single-crystal silicon layers grown atop an implanted pinning region, an absorber layer of each photosensor underlying the pinning region.
A method designated BB including the method designated B or BA wherein the thick overlying silicon filter layer is approximately 1.2 microns thick.
A method designated BC including the method designated B, BA, or BB wherein the thin overlying silicon filter layer is approximately 0.6 microns thick.
A method designated BD including the method designated B, BA, BB, or BC and further including passing the red, green, and blue signals through color correction circuitry to improve color resolution of the image.
A method designated BE including the method designated BD wherein the color correction circuitry is configured such that a corrected green output signal is determined by subtracting a multiple of the red signal from a multiple of the green signal.
Changes may be made in the above methods and systems without departing from the scope hereof. It should thus be noted that the matter contained in the above description and shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.