Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-05-12
2002-10-22
Epps, Georgia (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S336100
Reexamination Certificate
active
06469301
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to, inter alia, radiation-sensing detectors comprising one or more individual detector elements (“pixels”) each including a thermally displaceable member. Incident radiation such as infrared radiation is locally absorbed and converted to heat by the thermally displaceable elements, causing the thermally displaceable elements to individually exhibit a corresponding thermal displacement. The displacements impart corresponding changes to a signal light or other detectable entity.
BACKGROUND OF THE INVENTION
Conventional infrared-sensor panels include an array of a large number of individual sensor elements (“pixels”). Each pixel comprises a membrane portion that includes a planar surface made from one or more membrane layers. The membrane portion is suspended in space relative to a respective substrate in the manner of, e.g., a cantilever, and typically is made using micro-machining technology such as technology used in the manufacture of semiconductor integrated circuits.
For example, one type of conventional pixel in such an array includes a displaceable membrane member that is supported relative to a substrate by a leg portion. The displaceable membrane member includes a radiation-absorbing region. As the radiation-absorbing region absorbs incident electromagnetic radiation (e.g., infrared (IR) radiation), the displaceable membrane member exhibits a corresponding displacement relative to the substrate. Such elements have been incorporated into capacitor-based as well as light-based thermal-type IR detectors. See, e.g., U.S. Pat. Nos. 3,896,309 and 5,844,238; and U.S. patent application Ser. No. 08/994,949, now U.S. Pat. No. 6,080,988. In other conventional applications, the membrane member has been incorporated into the leg portion of a thermal-type displaceable element. A capacitor-based radiation detector reads out displacements to individual constituent pixels (caused by incident radiation) as respective changes of capacitance. A light-based radiation detector reads out displacement to individual constituent pixels (caused by incident radiation) as respective changes in a read-out (signal) light.
According to conventional practice, the membrane member typically includes a planar-surface portion formed from at least one layer having a desired planar configuration. In such a configuration, it is desirable that the membrane portion be as thin as possible to reduce the mass of the displaceable membrane member and thus to improve responsivity. However, conventional approaches exploited to achieve this end are not satisfactory.
In a radiation detector such as an IR detector, the rate at which incident radiation is absorbed by each pixel desirably is high to enhance detection sensitivity. It also is desirable that the thermal capacity of the radiation-absorbing region of each pixel be as small as practicable to enhance detection response. It also is desirable that the heat generated in each radiation-absorbing region be efficiently and effectively conducted to the respective displaceable member to enhance detection sensitivity.
In a conventional radiation detector, even if a gold-black membrane exhibiting a relatively high rate of radiation absorption rate is used as the radiation-absorbing region, it has not been possible to date to enhance both detection sensitivity and detection response of the pixels. More specifically, the rate of radiation absorption exhibited by gold black is, for example, about 960 cm
−1
with incident IR radiation having a wavelength in the range of 8 to 12 &mgr;m. Zaeschmar and Nedoluha, “Theory of the Optical Properties of Gold Blacks,”
J. Am. Opt. Soc.
62(3):348-352, March 1972. The efficiency with which gold black (formed as a 1-&mgr;m thick membrane) absorbs infrared radiation is only about 9%. Increasing the efficiency can be achieved by increasing the thickness of the gold-black membrane. However, this remedy leads to other problems. Conventionally, it is impossible both to reduce the membrane thickness while simulaneously enhancing the rate of absorption of IR radiation simply by forming the membrane in a manner such that the incident radiation merely enters the membrane. Hence, it is currently impossible to enhance both detection sensitivity and detection response of these detectors.
SUMMARY OF THE INVENTION
In view of the shortcomings of the prior art as summarized above, an object of the present invention is to provide, for a radiation detector, a displaceable structure of which the thickness (and thus the mass) can be reduced while maintaining a desired mechanical strength of the displaceable structure. Another object is to provide a thermal-type displaceable element, and a radiation detector comprising one or more such elements, exhibiting enhanced image-sensing performance while maintaining a desired mechanical strength and reducing the thickness of the displaceable element.
According to one aspect of the invention, a radiation detector is provided that includes a displaceable member. The displaceable member comprises a planar portion comprising at least one membrane layer. The planar portion is supported so as to be suspended over a substrate of the detector. The planar portion includes a “dropping portion” or “rising portion” extending along at least a portion of the periphery of the planar portion. The planar portion can be fabricated using a semiconductor-fabrication process. The dropping or rising portion desirably is formed of at least one layer of the planar portion.
By placing the dropping or rising portion around at least a portion of the periphery of the planar portion, the planar portion is structurally reinforced by the dropping or rising portion. This structural reinforcement allows the thickness (and thus the mass) of the planar portion to be reduced without compromising its mechanical strength. Also, the dropping or rising portion helps maintain uniformity of the planar portion, even if the planar portion is formed of multiple membrane layers.
If the planar portion is formed of multiple membrane layers, it can be peripherally edged in a manner in which at least one of the layers covers the peripheral edge of at least one of the other layers. Such a structure can be fabricated using a semiconductor-fabrication process. Because the planar portion is structurally reinforced by the covered edge of at least one layer, the thickness (and thus the mass) of the planar portion can be reduced without compromising the mechanical strength of the planar portion.
Furthermore, even if the planar portion would otherwise tend to exhibit a displacement due to any difference in the coefficients of thermal expansion of the layers making up the planar portion, such displacement is arrested by the strength imparted by the covered peripheral edges.
A thermal-type displaceable element of a radiation detector according to the invention can comprise a leg serving to connect the displaceable element to the substrate and to suspend the displaceable element over a corresponding region of the substrate. The leg can comprise at least one membrane layer and can be fabricated as an extension of the planar portion. The leg desirably has a thermal-insulation property. The greater the thermal insulation provided by the leg, the greater the displacement that can be imparted to the displaceable element. The leg also can include a dropping portion extending around a planar portion of the leg, so as to provide the leg with enhanced structural rigidity while allowing the membrane thickness of the leg to be reduced. By reducing the thickness of the leg, its thermal-insulation property can be enhanced.
The radiation detector can comprise a thermal-type displaceable element comprising a displaceable portion that is displaced according to heat generated by incident light (e.g., IR light). The displaceable portion is displaced (e.g., tilted) by an amount corresponding to the amount of generated heat. As an alternative to IR radiation, the detector can be configured to undergo heating in response to other wavele
Ishizuya Tohru
Suzuki Junji
Klarquist & Sparkman, LLP
Nikon Corporation
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