Abstract:
A low-cost infra-red detector is disclosed including a method of making and using the same. The detector employs a substrate, a filtering layer, a converting layer, and a diverter to be responsive to wavelengths up to about 1600 nm. The detector is useful for a variety of applications including spectroscopy, imaging, and defect detection.

Description:
This invention was made with Government support under Contract DE-AC06-76RLO1830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an infra-red detector and a method of making and using the same. 
     SUMMARY OF THE INVENTION 
     An infra-red detector is disclosed comprising a substrate responsive to electromagnetic radiation in a first wavelength region; a filtering layer operably disposed on the substrate transparent to electromagnetic radiation in the first wavelength region and attenuating to electromagnetic radiation shorter than those in the first region; a converting layer operably disposed on the filtering layer emitting electromagnetic radiation in the first wavelength region when wavelengths longer than those in the first wavelength region are incident thereon; and, a diverting means whereby radiation emitted from the converting layer is directed to the substrate generating an electronic signal therein proportional to the incident radiation for detection. The method of making the detector, in one embodiment, comprises: providing a substrate for detecting electromagnetic radiation in a first wavelength range; providing a filtering layer operably disposed on the substrate for converting and emitting electromagnetic radiation in the first wavelength region when wavelengths longer than those in the first region are incident thereon; providing a converting layer operably disposed on the filtering layer for filtering wavelengths shorter than those in the first region therefrom; and, providing a diverting means whereby emitted radiation is directed to the substrate whereby an electronic signal proportional to the incident radiation is generated in the detector and detected. 
     In an embodiment, the detector is a component of a spectrometer instrument. 
     In a further embodiment, the detector is a component of an event discrimination system or device. 
     In yet another embodiment, the detector is a component of an imaging system or device. 
     In yet another embodiment, the detector is a component of a defect detection system or device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  illustrates an infra-red detector according to an embodiment of the invention. 
         FIG. 1   b  illustrates an infra-red detector according to a further embodiment of the invention. 
         FIG. 1   c  illustrates an infra-red detector comprising a diode array according to yet another embodiment of the invention. 
         FIG. 1   d  illustrates an infra-red detector comprising a luminescent fiber according to yet another embodiment of the invention. 
         FIG. 1   e  illustrates an infra-red detector comprising a planar wave guide according to still yet another embodiment of the invention. 
         FIG. 2  illustrates a signal response for a filtering layer of the detector exhibiting a cutoff of about 400 nm, according to an embodiment of the invention. 
         FIG. 3  illustrates a frequency conversion system for populating trapping states within a converting layer of an infra-red detector according to one embodiment of the invention. 
         FIG. 4   a  illustrates a wavelength response for a substrate of an infra-red detector according to an embodiment of the invention. 
         FIG. 4   b  illustrates a signal response added to an infra-red detector according to a further embodiment of the invention. 
         FIG. 5  illustrates a spectrometer instrument incorporating an infra-red detector of the invention. 
         FIG. 6  illustrates a system for discriminating events according to an embodiment of the method of use of the invention. 
         FIG. 7  illustrates a system for imaging according to a further embodiment of the method of use of the invention. 
         FIG. 8  illustrates a system for detecting defects according to yet a further embodiment of the method of use of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     While the present invention is described herein with reference to the embodiments thereof, it should be understood that the invention is not limited thereto, and various alternatives in form and detail may be made therein without departing from the spirit and scope of the invention. All such modifications as would be envisioned by the person of ordinary skill in the art are hereby incorporated. 
       FIG. 1   a  illustrates an infra-red (IR) detector  100  according to an embodiment of the invention. The detector  100  comprises a substrate  110  responsive to electromagnetic radiation having wavelengths  120  in a first wavelength range from about 400 nm to about 1100 nm, e.g., in the visible to near-infra-red spectrum. The substrate  110  comprises at least one semiconductor material, including but not limited to, silicon (Si), gallium arsenide (GaAs), germanium (Ge), or combinations thereof. 
     The detector  100  further comprises a filtering layer  140  disposed between substrate  110  and converting layer  115  for filtering wavelengths shorter than those in the first wavelength region, e.g., filtering UV radiation as background signal noise, and transmitting longer wavelengths. Materials within layer  140  provide attenuation of any excitation UV radiation while allowing-longer wavelengths to reach the substrate  110  thereby providing a filtering capability. Materials suited for use within filtering layer  140  include, but are not limited to, metal oxides, Ta 2 O 5 , SnO 2 , ZnO, and InSb. Other materials providing filtering capability may be chosen as would be selected by the person of ordinary skill in the art. Materials comprising the substrate  110  may be deposited via standard techniques known in the art, including, but not limited to, powder casting on a tape matrix, vapor sputtering, vapor deposition, and vacuum evaporation deposition. Alternately, filtering layer  140  may be optically linked to substrate  110 . Thus, no limitation is intended by the disclosed materials or configurations described herein. 
     Thickness of layer  140  is dependent on the materials used and/or the properties desired. For example, ZnO provides about 95% attenuation for UV light up to about 340 nm at a thickness of about 30 nm, but is not limited thereto. In particular, thickness of layer  140  is in the range from about 10 nm to about 100 nm. More particularly, thickness is in the range from about 10 nm to about 50 nm. Most particularly, thickness is in the range from about 10 nm to about 30 nm. 
     The detector  100  further comprises a converting layer  115  operably disposed with filtering layer  140  for converting wavelengths of incident radiation  120  longer than those in the first wavelength region, e.g., upconverting wavelengths in the infra-red spectrum, to wavelengths in the first region, e.g., to visible spectrum wavelengths  125 , and emitting the converted radiation, as detailed hereinbelow. Converting layer  115  comprises materials including, but not limited to, phosphors, cubicY 2 O 3 :Tb 3+ /SiO 2  inverse photonic lattice materials, rare-earth ion-doped solid state materials, mixed rare-earth oxides, electroluminescent polymers, photoluminescence materials, poly[2-methoxy,5-(2′-ethyl-hexyloxy)-p-phenylenevinylene] (MEH-PPV), poly(p-phenylenevinylene) (PPV), upconverting dyes, upconverting fluorophores, upconverting polymers, liquid crystal materials, two--r-conjugated organic materials, converting nanoparticles, converting gases, electrophoretic materials, converting uoropores, piezoelectric materials, electron trapping materials, SiGe, metal halide luminescent materials, photorefractive materials, Tm 3+  doped Ba—Y—Yb—F thin films, high-Z materials, solid-state materials, and combinations thereof. Thicknesses for converting layer  115  are selected based on desired properties. In particular, thickness of converting layer  115  is in the range from about 1 μm to about 100 μm. More particularly, thickness is in the range from about 1 μm to about 40 μm. Converting materials are disposed onto or operably connected to the substrate via standard techniques known in the art, including, but not limited to, powder casting on a tape matrix, vapor sputtering, vapor deposition, and vacuum evaporation deposition. Thus, no limitation is intended by the methods disclosed herein. 
     A light source  130  optically disposed with the converting layer  115  transmits light  135  through layer  115  populating trapping states therein with electrons near the conduction band, as described below. Sources include, but are not limited to, intermittent sources, pulsed sources, timed sources, and continuous sources as implemented in the art. Thus, no limitation is hereby intended by the embodiments and examples disclosed herein. In one example, the light source  130  is a blue light-emitting-diode (LED). In another example, light source  130  is a ultra-violet (UV) radiation source. 
     The detector  100  further comprises an electromagnetic energy diverting means  145  for directing radiation emitted from the converting layer to the substrate  110  generating an electronic signal (i.e., detector signal)  150  therein proportional to the incident radiation. Diverting means  145  include, but are not limited to, scintillating fibers, light pipes, wave guides, and combinations thereof. Detector signal  150  is detected by standard signal electronics  155  and/or components known in the art. Processing of signal  150  may further be done using signal processing components  156  or equipment, e.g., a CPU or computer, as will be selected by the person of ordinary skill in the art. No limitations are hereby intended. 
     In a further embodiment of the invention illustrated in  FIG. 1   b,  the detector  100  substrate  110  comprises silicon. The detector  100  further comprises a housing member  160 , and circuit interconnects  165  operable for connecting detector  100  for use in devices and instruments, e.g., a spectrometer instrument, as described further hereinbelow. 
     In yet another embodiment illustrated in  FIG. 1   c,  substrate  110  comprises a two-dimensional array  112  selected from, e.g., diode arrays and linear arrays, further comprising any operable semiconductor material, e.g., silicon. In the instant embodiment, filtering layer  140  comprises a visible-light transparent, UV-attenuating material  142  as described herein, layer  140  being operably disposed between a two-dimensional array  112  and conversion layer  115 , e.g., as a coating on substrate  110 . Thickness of layers  115  and  140  is optimized for minimizing background signal noise and maximizing emission, collection, and detection of visible light by the two-dimensional array  112 . Detector signal  150  is detected by standard signal electronics  155  and/or components known in the art. Processing of signal  150  is done using standard signal processing components or equipment  156 , e.g., a CPU or computer, as will be selected by the person of ordinary skill in the art. No limitations are hereby intended. 
     In yet another embodiment illustrated in  FIG. 1   d,  the detector  100  is configured with a commercially available fiber  145  [e.g., CeramOptec GmbH, Bonn, GE] as a diverting means  145  optically linked to converting layer  115 . Fiber  145  has an I.D. and O.D that couples and numerically-aperture-matches the thickness of conversion layer  115  such that emitted light is efficiently captured and effectively channeled to substrate  110  for detection. Fibers suited for diverting light to detector  100  are selected from the group consisting of optical fibers, step-index fibers, single-mode step index fibers, multimode step index fibers, and graded-index fibers. In one exemplary configuration, light from fiber  145  is collimated using a GRIN lens  113  at a pitch of 0.25, e.g., a separate fiber cut to a length of one quarter of the pitch of the fiber. Light exiting fiber  145  can be collimated into a parallel beam when the output end of the fiber is connected to the GRIN lens  113 . Detector signal  150  is detected by standard signal electronics  155  and/or components known in the art. Processing of signal  150  may further be done using signal processing components  155  or equipment  156 , e.g., a CPU or computer, as will be selected by the person of ordinary skill in the art. No limitations are hereby intended. 
     In yet another embodiment illustrated in  FIG. 1   e,  detector  100  is configured with a waveguide  145  as a diverting means  145  optically linked to converting layer  115  for diverting UV light to converting layer  115 . In one exemplary example, waveguide  145  is disposed between substrate  110  and filtering layer  140 . Waveguide  145  is of a thickness of at least about one-quarter wavelength with a “cladding” thickness sufficiently thin permitting optical transmission of wavelengths to the substrate  110 . Waveguides suitable for use include, but are not limited to, planar waveguides, rectangular waveguides, square waveguides, optical waveguides, and/or combinations thereof. Waveguides may be used in combination with suitable optics for directing and/or converging incident radiation in and through the waveguide to the substrate, including, but not limited to, e.g., gratings, prisms, mirrors, and/or lenses. All configurations and/or component combinations as would be envisioned or implemented by the person of ordinary skill in the art are incorporated herein. Detector signal  150  is detected by standard signal electronics  155  and/or components known in the art. Processing of signal  150  is done using signal processing components or equipment  156 , e.g., a CPU or computer, as will be selected by the person of ordinary skill in the art. No limitations are hereby intended. Operation of the filtering layer  140  and transmission of incident radiation through the layer will now be further described by reference to  FIG. 2 . 
       FIG. 2  illustrates a typical filtering response of filtering layer  140  showing expected transmittance (T) as a function of wavelength, wherein transmittance plus reflectance plus absorbance equals a value of unity (i.e., 1), and wherein absorbance equals emittance. In the figure, incident radiation below a wavelength of about 1100 nm is attenuated or filtered, while wavelengths above about 1100 nm, e.g., infra-red wavelengths, are transmitted through the layer. Layer  140  prevents UV excitation wavelengths causing signal noise from being detected in the substrate  110 . In particular, layer  140  has a long-pass cutoff less than or equal to about 400 nm depending on the incident UV excitation wavelengths thereby permitting only desired visible wavelengths emitted from conversion layer  115  to be detected in substrate  110 . The response is Illustrative of long-band-pass filtering materials suitable for use in detector  100 . Thus, any filtering material passing or transmitting visible wavelengths to the substrate  110  is suitable for use in the present invention. In particular, materials having various cutoff wavelengths may be selected whereby layer  140  exhibits long-band-pass filtering properties for wavelengths in the range from about 300 nm to about 400 nm. More particularly, cutoffs may be selected at wavelengths in the range from about 350 nm to about 400 nm. Thus, no limitation is hereby intended. Wavelength conversion will now be described in more detail with reference to  FIG. 3 . 
       FIG. 3  illustrates but one of a plurality of wavelength or frequency conversion mechanisms operable within a converting layer  115 . Electrons populating ground energy states  305  within the layer  115  are promoted to a plurality of trapping states  310  close to the conduction band  330 . Need for UV filtering is demonstrated in cases where promotion of electrons occurs in multiple-stages, e.g., in two stages, whereby a first stage transitions electrons to the conduction band via UV radiation excitation, followed by natural decay of electrons in a second stage to fill the trapping states. Natural or induced defects in converting layer  115  at the molecular level form the trapping states  310 . Electrons are promoted to the trapping states  310  in the converting layer  115  by exposing the layer to a radiation source  130 , e.g., an LED or UV source, emitting electromagnetic radiation  135  having wavelengths less than or equal to about 400 nm such that trapping states  310  are optimally filled with electrons. When IR radiation  325  having wavelengths of from about 1100 nm is incident on the converting layer  115 , electrons in trapping states  310  are promoted to conduction band  330  (radiative state) with a corresponding change in frequency (i.e., upconversion) resulting in emission of photons whose decay emits wavelengths  125  in the visible spectrum. Visible light emitted through photon decay is detected being proportional to the incident IR radiation  325 . Spectral response of detector  100  will now be described with reference to  FIGS. 4   a – 4   b.    
       FIG. 4   a  illustrates a typical unmodified wavelength response for layer  110  before incorporation in detector  100  of the present invention, having a wavelength response in the range from about 400 nm, with a signal cutoff of about 1000 nm.  FIG. 4   b  illustrates the expected signal response added to the operable detector of the present invention, showing a rise in detector response beyond the cutoff in  FIG. 4   a.  In the instant example, the detector is responsive and operable in the range from about 400 nm to about 1600 nm using readily available materials. 
       FIG. 5  illustrates a spectrometer instrument  510  incorporating a IR detector  100  according to one embodiment of the method of use of the invention. Instruments suited for use with detector  100  are selected from the group consisting of Fourier Transform spectroscopy instruments, Static Fourier Transform spectroscopy instruments, event discrimination or time-domain instruments (e.g., gunshot identification instrumentation), imaging instruments (e.g., imaging CCD instruments), phase measurement instruments (e.g., holographic inspection instruments and conventional FT spectrometers), including components thereof. No limitation in classes of instruments is intended by the disclosure herein. Detector  100  is operably connected in instrument  510  via circuit interconnects  165  standard in the art. Detector signal  150  is detected by standard signal electronics and/or components  155  known in the art. Processing of signal  150  may further be done using signal processing equipment  156  and/or components as will be selected by the person of ordinary skill in the art. For example, instrument  510  and signal electronics  155  may be interfaced to, or operated in conjunction with, e.g., a computer  156  or other operating and/or processing equipment implemented by the person of ordinary skill. No limitations are hereby intended by the disclosure herein. 
     In one embodiment according to the method of use, illustrated in  FIG. 6 , detector  100  is a component of an event discrimination system or device  610 . For example, differences in time domain behavior of infrared (IR) radiation emitted from, e.g., a gunshot event  615  and/or a glint (e.g., flash of light) event  620  are illustrative. IR radiation  625  and  630  emitted from the separate events reaches the detector  100  whereby characteristics of the radiation including, but not limited to, e.g., wavelength, e.g.,  632  and  634 , and distance, e.g.,  636  and  638 , permit event  615  to be discriminated and characterized from event  620 . Differences quantified using collected data permits the characterization and/or discrimination of events. Data for discriminating and/or characterizing events include, but are not limited to, e.g., wavelength (λ), timing, emissivity (ε), frequency (f), time-of-flight (t), transmittance (T), angles of incidence (θ), phasing, reflectance, index of refraction (n), and intensity. Analysis of data may be done in conjunction with a computer and/or other data processing system  156 . 
     In yet another embodiment illustrated in  FIG. 7 , detector  100  is a component of an imaging system or device  710 . In but one illustrative example, gas clouds  715 ,  720 , and  725  are illustrated representative of a plurality of possible gaseous sources, including, but not limited to, e.g., gas plumes, main ruptures, manufacturing breaches, storage tank releases, transport accidents, production upsets, and/or emission events. Clouds  715 ,  720 , and  725  emit wavelengths  730 ,  735 , and  740 , respectively, characteristic of the material in the cloud and/or characteristic of the given event which is measured and analyzed. In particular, detector  100  of system  710  detects incident radiation generating signals representative of the intact gas cloud(s), streams, or event(s) whereby images and/or event data may be compiled and analyzed. In the system illustrated, the detector is used in conjunction with various filters, e.g.,  745 ,  750 , and  755 , and/or other system components for discriminating and/or characterizing the radiation events, including, but not limited to, long-band-pass filters, optical filters, polarizers, lenses, sensors, and the like, including combinations thereof, as would be implemented by the person of ordinary skill in the art. Thus, no limitation is hereby intended. Image analyses comprises measurement of event characteristics including, but not limited to, wavelength determination, time-of-flight, intensity, interference patterns, holographic patterns, phase measurement patterns, polarization patterns, wavelength patterns, time scales, and combinations thereof, e.g., polarization intensity. Signal processing and/or instrument control may be performed in conjunction with a computer or other processing system  156 . 
     In yet another embodiment illustrated in  FIG. 8  according the method of use, detector  100  is a component of a defect detection system or device  810  for detecting defects including, but not limited to, manufacturing defects. In but one example, manufactured items, e.g., a sprocket  825 , is interrogated using a first radiation wavelength  815  which impinges the sprocket at a characteristic first angle (θ 1 )  817  with respect to the surface horizontal. Reflected wavelength  820  is measured with respect to the surface horizontal at a second angle (θ 2 )  822  and detected using system  810 . Interrogation may be performed in conjunction with, e.g., rotation of the item, to identify all manufacturing or other defects on all surfaces. Differences in collected data are compared against identical control items and data. Tolerances and standards as utilized and/or known in the art would identify defective items. Signal processing may be done in conjunction with signal processing equipment  156 , e.g., a computer, as will be known in the art. 
     While the present invention has been described herein with reference to various embodiments thereof, it should be understood that the invention is not limited thereto, and various alternatives in form and detail may be made therein without departing from the spirit and scope of the invention. In particular, those skilled in the art will appreciate that.