Micromachined pyro-optical structure

Details Micromachined pyro-optical structure Micromachined pyro-optical structure

2002-01-14

2004-08-03

Le, N. (Department: 2859)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250S332000, C250S351000

Reexamination Certificate

active

06770882

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates generally to thermal sensing of low-level radiation of infrared or millimeter wavelengths and more particularly to a pyro-optical pixel structure and focal plane array with means for maintaining a nominal temperature. This invention describes a method of sensing incident radiation using a highly sensitive thermal thin film structure. In its embodiment as an array, a thermal image obtained typically from infrared wavelengths is interrogated using an optical carrier beam and readout with conventional CCD or CMOS silicon imagers.
STATEMENT REGARDING FEDERALLY SPONSORED R&D
Work leading to this invention was not funded by the US Government.
BACKGROUND OF THE INVENTION
Thermal-based sensor systems typically use a pixel that is highly sensitive to temperature differentials. This minute temperature differential is read out using conversion techniques into an electrical signal. The basic components for a thermal imaging system generally include optics for collecting and focusing the incident irradiation from a scene onto an imaging focal plane. A chopper is often included in a thermal imaging system to produce a constant background radiance which provides a reference signal. The electronic processing portion of the thermal imaging system will subtract the reference signal from the total radiance signal to produce an output signal with a minimum background noise level.
The concept of using a pyro-optical material as a sensor to detect radiation by modulating a carrier beam was first disclosed by Elliott in U.S. Pat. No. 4,594,507. This concept is cited as prior art in
FIG. 1
as an architectural representation of a system with an optical carrier source
1
and an external radiation source
2
illuminating a pyro-optical pixel
3
with a photodetector
4
to monitor the amplitude of the carrier source
2
modulated by the transmissivity of the pyro-optical pixel
3
. In this example the low level radiation source is focused onto the pyro-optical plane
3
through refractory lens
5
. The present invention is an improved sensor pixel based on the concept of FIG.
1
. The present invention describes a micromachined pixel containing a pyro-optical film integral to a thermally isolated platform and positioned above a temperature-referenced substrate.
The thermal imager of Elliott (U.S. Pat. No. 4,594,507) includes a preferred embodiment of an optically active nematic crystal with a polarizer analyzer that is illuminated from an external light source of unspecified type. This thermal imager operates with an external photodetector of unspecified type illuminated by the external light source through the nematic, temperature-sensitive crystal. The result is an image converter operating with the nematic crystal as the modulator. The system detailed by Elliott operates within an oven typically at 28 deg C. and is specified for imaging infrared irradiation only. Individual pixel structures are not disclosed or claimed and thus items such as separate pixel heaters and micromachined structures are not embodied in this invention. The Elliott system does not use compactness of construction since the external light source and photodetector are not integrated into the structure containing the nematic liquid crystal. Thermal isolation structures surrounding the nematic crystal film and any specific type of optical light source are not mentioned. Performance-enhancing interferometric structures are not mentioned.
Hanson in U.S. Pat. No. 5,512,748 discloses a thermal imaging system containing a focal plane array in which a visible or near-infrared source is used to transfer an image from a transmissivity-modulated pyro-optical film layer onto an associated integrated circuit photodetector. The photodetector integrated into the substrate generates a bias signal representing the total radiance imaged from a remote low-level scene. A thermal sensor is described which contains infrared-sensitive material supported by two bifurcated support arms and nonflexing posts to maintain this film layer above the substrate with a gap therebetween. The thickness of the infrared-sensitive material is not mentioned except to note that it is preferably “very thin to enhance it's response to incident infrared radiation and to allow transmission of electromagnetic energy therethrough” (col. 7, line 8) without mention of Fabry Perot characteristics. The gap under the sensitive film is said to preferably correspond to ¼ wavelength of the selected infrared incident radiation wavelength to provide maximum reflection of the infrared from the semiconductor substrate to the infrared-sensitive film. Hanson does not disclose or claim the use of electrical heater elements or any means of temperature control within or without the infrared sensitive pixel. Hanson does not disclose or claim the use of vacuum surrounding the infrared-sensitive pixel.
Owen in U.S. Pat. No. 6,087,661 describes a structure with electrically conducting tetherbeams forming a signal flow path for readout from a pyroelectric pixel material. The tetherbeams further provide a thermal isolation for the pyroelectric sensor microplatform.
Ruffner et al in U.S. Pat. No. 4,751,387 describes the use of a silica foam called aerogel as a solid, thermal isolation film formed between the pyroelectric capacitor and an underlying substrate as part of a specific infrared-sensitive pixel design without claims describing components external to the pixel. The use of pyro-optical sensitive materials is not disclosed or claimed. The Ruffner patent does not mention heating elements or ovens, vacuum conditions, the use of any optical carrier interrogation beams, pyro-optical materials, or the use of performance-enhancing interferometric structures.
Robillard in U.S. Pat. No. 4,751,387 describes an infrared imaging system comprising a pyro-optic film consisting of dichroic liquid crystal coated on a membrane with a means of polarized visible light illumination onto the crystal film. In addition a means for analyzing the polarization of the visible light carrier after reflection from or transmission through the crystal film is included in a system where the readout described is the human eye. Robillard does not disclose or claim any micromachined structures, thermal isolation structures, the use of partial vacuum, ovens, or pixel heaters.
Cross in U.S. Pat. No. 4,994,672 describes an infrared imaging system including a sandwich structure of polarizing pyro-optic material formed over an optically transparent, thermally insulating foam such as silica aerogel. The reflectance (not transmission) of an interrogating light beam is modulated by the temperature of the material and is used to illuminate a pixel image onto a CCD. A container means is provided for enclosing the pyro-optical material and maintaining a stable temperature. The Cross system requires the use of polarized light. The present invention does not utilize the polarization of light. Cross does not modulate the transmission of the interrogating optical beam. Cross does not disclose the use of micromachined pixel structures, performance enhancing interferometric structures, vacuum conditions surrounding the pyro-optic material.
Tuck in U.S. Pat. No. 5,100,218 describes a specific thermal imaging system based on the thermal rotation of polarized light as it is modulated with transmission through a thermally-sensitive liquid crystal. The pyro-optical liquid crystal is separated from the optical source and photodetector by multiple lenses and thus is not a composite, sandwich structure integrating the optical carrier source and photodetectors. Liquid crystal is the only pyro-optical material mentioned. Pyro-optical materials that do not require polarization are not disclosed. Tuck does not disclose any micromachined structures, interferometric structures, any means of controlling ambient temperature, or operation with partial vacuum conditions.
Carr in U.S. Pat. No. 6,091,050 describes a micromachined platform that elevates automatically and without continuing po

Affiliated with

Also associated with

Rating

Micromachined pyro-optical structure does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Micromachined pyro-optical structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Micromachined pyro-optical structure will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3356172