Intensified hybrid solid-state sensor with an insulating layer

Details Intensified hybrid solid-state sensor with an insulating layer Intensified hybrid solid-state sensor with an insulating layer

2001-10-09

2004-06-08

Allen, Stephone B. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

C250S2140VT, C313S1030CM, C348S217100

Reexamination Certificate

active

06747258

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to an intensified hybrid solid-state sensor. More particularly, the present invention relates to an image intensifier using a CMOS or CCD sensing device connected in close physical proximity to a microchannel plate (MCP) and photo cathode.
BACKGROUND OF THE INVENTION
The present invention relates to the field of image intensifying devices using solid-state sensors, such as a CMOS or CCD device. Image intensifier devices are used to amplify low intensity light or convert non-visible light into readily viewable images. Image intensifier devices are particularly useful for providing images from infrared light and have many industrial and military applications. For example, image intensifier tubes are used for enhancing the night vision of aviators, for photographing astronomical bodies and for providing night vision to sufferers of retinitis pigmentosa (night blindness).
There are three types of known image intensifying devices in prior art; image intensifier tubes for cameras, all solid-state CMOS and CCD sensors, and hybrid EBCCD/CMOS (Electronic Bombarded CCD or CMOS sensor).
Image intensifier tubes are well known and used throughout many industries. Referring to
FIG. 1
, a current state of the prior art Generation III (GEN III) image intensifier tube
10
is shown. Examples of the use of such a GEN III image intensifier tube in the prior art are exemplified in U.S. Pat. No. 5,029,963 to Naselli, et al., entitled REPLACEMENT DEVICE FOR A DRIVER'S VIEWER and U.S. Pat. No. 5,084,780 to Phillips, entitled TELESCOPIC SIGHT FOR DAYLIGHT VIEWING. The GEN III image intensifier tube
10
shown, and in both cited references, is of the type currently manufactured by ITT Corporation, the assignee herein. In the intensifier tube
10
shown in
FIG. 1
, infrared energy impinges upon a photo cathode
12
. The photo cathode
12
is comprised of a glass faceplate
14
coated on one side with an antireflection layer
16
, a gallium aluminum arsenide (GaAlAs) window layer
17
and gallium arsenide (GaAs) active layer
18
. Infrared energy is absorbed in GaAs active layer
18
thereby resulting in the generation of electron/hole pairs. The produced electrons are then emitted into the vacuum housing
22
through a negative electron affinity (NEA) coating
20
present on the GaAs active layer
18
.
A microchannel plate (MCP)
24
is positioned within the vacuum housing
22
, adjacent the NEA coating
20
of the photo cathode
12
. Conventionally, the MCP
24
is made of glass having a conductive input surface
26
and a conductive output surface
28
. Once electrons exit the photo cathode
12
, the electrons are accelerated toward the input surface
26
of the MCP
24
by a difference in potential between the input surface
26
and the photo cathode
12
of approximately 300 to 900 volts. As the electrons bombard the input surface
26
of the MCP
24
, secondary electrons are generated within the MCP
24
. The MCP
24
may generate several hundred electrons for each electron entering the input surface
26
. The MCP
24
is subjected to a difference in potential between the input surface
26
and the output surface
28
, which is typically about 1100 volts, whereby the potential difference enables electron multiplication.
As the multiplied electrons exit the MCP
24
, the electrons are accelerated through the vacuum housing
22
toward the phosphor screen
30
by the difference in potential between the phosphor screen
30
and the output surface
28
of approximately 4200 volts. As the electrons impinge upon the phosphor screen
30
, many photons are produced per electron. The photons create the output image for the image intensifier tube
10
on the output surface
28
of the optical inverter element
31
.
Image intensifiers such as those illustrated in
FIG. 1
have advantages over other forms of image intensifiers. First, intensifiers have a logarithmic gain curve. That is, the gain decreases as the input light level is increased. This matches the human eye response particularly when bright lights are in the same scene as low lights. Most solid-state devices have a linear response; i.e., the brighter the light the brighter the output signal. The result is that bright lights appear much brighter to a viewer of a solid-state system and tend to wash out the scene. Solid-state sensors can be modified to produce a gain decrease as input light is increased, however, this requires changing the amplifier gain, using shuttering, or using anti-blooming control.
Another advantage of image intensifiers is the ability to function over a large range of input light levels. The power supply can control the cathode voltage and thereby change the tube gain to fit the scene. Thus tubes can function from overcast starlight to daytime conditions.
However, image intensifier/I
2
cameras suffer from numerous disadvantages. The electron optics of the phosphor screen produces a low contrast image. This results in the object looking fuzzier to the human observer, or solid-state sensor, when viewed through an image intensifier. Although this deficiency has been somewhat reduced with further image intensifier development, solid-state imagers generally have better performance.
Another disadvantage with image intensifier/I
2
cameras is “halo.” Halo results from electrons being reflected off either the MCP or the screen. The reflected electrons are then amplified and converted into light in the form of a ring around the original image. In image tubes, the halo from electrons reflected from the MCP has been reduced to a negligible effect for the most recent production tubes. However, the halo from the screen section still exists, although not to the degree of the cathode halo. Nevertheless, the screen halo is still a significant defect in imaging systems when a CCD or CMOS array is coupled to the image intensifier. This is because these arrays are more sensitive than the eye to the low light levels in the screen halo.
Another disadvantage is that image intensifiers do not have a method of providing electronic read-out. Electronic read-out is desired so that imagery from thermal sensors may be combined with intensified imagery with the result that the information from both spectra will be viewed at the same time. One solution has been to create an I
2
camera by coupling a CCD or CMOS array to an image intensifier tube. When a solid-state device is coupled to an image tube the resultant camera has all performance defects of the image tube that is low contrast, often poor limiting resolution due to coupling inefficiencies and the added cost of the image tube to the camera.
Solid-state devices typically include CCD or CMOS sensors. They function by directly detecting the light, electronically transferring the signal to solid-state amplifiers, then displaying the image on either a television type tube or display such as a liquid crystal display.
FIGS. 2
a
and
2
b
illustrate a flow chart and schematic diagram for a typical CCD sensor.
CCD and CMOS sensors are solid-state devices; that is, there is no vacuum envelope and the output is an electronic signal that must be displayed elsewhere and not within the sensor. The solid-state devices operate with power of 5-15 volts. The light is detected in individual pixels as labeled “s” and translated into electrons that are stored in the pixel until the pixel is read out to the storage register. From the storage register the electronic information contained in multiple pixels is then transferred to a read out register and then to output amplifiers and then to a video display device such as a cathode ray tube.
The disadvantages of an all solid-state device are poor low light level performance, potential blooming from bright light sources, poor limiting resolution, and high power consumption. The poor low light performance is due to dark current and read-out noise resulting in low signal-noise ratios. If a signal gain mechanism were provided prior to read-out this issue would be negated, as sufficient signal would exist to o

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