DESCRIPTION

METHOD AND APPARATUS FOR INFRARED DETECTION AND DISPLAY

Cross-Reference to Related Applications

The present application claims the benefit of U.S. Application Serial No. 60/930,225, filed May 14, 2007, and claims the benefit of U.S. Application Serial No. 60/848,581, filed September 29, 2006, both of which are hereby incorporated by reference herein in their entirety, including any figures, tables, or drawings.

Background of Invention

There are many applications for detecting infrared (IR) radiation. IR can refer to radiation having wavelengths longer than visible light (> 0.7 μm) up to about 14 μm, with near- IR being a subset referring to wavelengths from about 0.7 μm to about 1.0 μm. One application is the detection of IR in environments with low ambient light, which can occur, for example, at night. It can also be useful to display to a user the image of the detected IR at a wavelength visible to the user. One common device for detecting IR images and displaying the detected images to a user is night-vision goggles.

Conventional night vision goggles are complex electro-optical devices that can require very high operating voltages and cost thousands of dollars. Typical night vision goggles intensify existing light instead of relying on their own light source and are sensitive to a broad spectrum of light, from visible through infrared. A conventional lens, called the objective lens, captures ambient light, including some near-infrared light. The gathered light is then sent to an image-intensifier tube. The tube outputs a high voltage, e.g., about 5,000 volts, to the image-tube components. The image-intensifier tube has a photo cathode, which is used to convert the photons of light energy into electrons. As the electrons pass through the tube, similar electrons are released from atoms in the tube, multiplying the original number of electrons by a factor of thousands through the use of a micro channel plate (MCP) in the tube. When the electrons from the photo cathode hit the first electrode of the MCP, they are accelerated into the glass micro channels by the 5,000-V bursts being sent between the electrode pair. As electrons pass through the micro channels, they cause thousands of other electrons to be released in each channel using a process called cascaded secondary emission. These new electrons also collide with other atoms, creating a chain reaction that results in

thousands of electrons leaving the channel where only a few entered. At the end of the image - intensifier tube, the electrons hit a screen coated with phosphors. These electrons maintain their position in relation to the channel they passed through, which provides a perfect image since the electrons stay in the same alignment as the original photons. The energy of the electrons causes the phosphors to reach an excited state and release photons. These phosphors create the green image on the screen that has come to characterize night vision. The green phosphor image is viewed through another lens called the ocular lens, which allows you to magnify and focus the image. The night vision device may be connected to an electronic display, such as a monitor, or the image may be viewed directly through the ocular lens. Accordingly, there is a need for IR sensors/detectors, and IR sensor/detector-display combinations, that operate at low operating voltages and are lightweight and cost-effective to produce.

Brief Summary Embodiments of the subject invention relate to a method and apparatus for infrared

(IR) detection. A specific embodiment utilizes organic layers to produce a phototransistor for the detection of IR radiation. The wavelength range of the IR detector can be modified by incorporating materials sensitive to photons of different wavelengths. In a specific embodiment, quantum dots of materials sensitive to photons of different wavelengths than the host organic material of the absorbing layer of the phototransistor can be incorporated into the absorbing layer so as to enhance the absorption of photons having wavelengths associated with the material of the quantum dots.

In another embodiment, a photoconductor structure can be used instead of a phototransistor. In one embodiment, the photoconductor can incorporate PbSe or PbS quantum dots. In another embodiment, the photoconductor can incorporate organic materials. Specific embodiments also involve displaying a detected IR image to a user. In a specific embodiment, organic materials can be used to create an organic light-emitting device. Additional material that emits at different wavelengths can be added to the light- emitting layer. In a specific embodiment, quantum dots of materials associated with emission of photons of different wavelengths than the host organic material of the emission layer can be incorporated into the emission layer to enhance the output display of the organic light- emitting device to the user. In a preferred embodiment, the IR detection is accomplished with a phototransistor and the displaying of the detected IR image is accomplished with an

organic light-emitting device such as an organic light-emitting diode (OLED). In a more preferred embodiment, the phototransistor and OLED are in series.

Embodiments of the subject invention pertain to a method and apparatus for night vision. In an embodiment, a night vision device can be accomplished by the deposition of layers of organic thin films. Embodiments of the subject device can operate at low operating voltages, such as 10-15 V. In addition, the cost of manufacturing specific embodiments of the subject device can be lower than the cost of manufacturing conventional night vision systems. In an embodiment of the subject night vision device an organic phototransistor can be in series with an organic light-emitting device, such as an organic light-emitting diode (OLED).

Brief Description of Drawings

Figure 1 shows an embodiment of a two-dimensional infrared image sensor/detector, a two-dimensional infrared image sensor/display array without pixelation, and a circuit model of the sensor/display array. Figure 2 shows a PNP bipolar phototransistor and an NPN bipolar phototransistor in accordance with embodiments of the subject invention.

Figure 3 shows an embodiment of an infrared image/sensor display array using PbSe quantum dots in the absorption layer.

Figure 4 shows an embodiment of the subject display device incorporating CdSe quantum dots in the emission layer.

Figure 5 shows materials that can be used in various embodiments of the subject invention.

Figure 6 shows an embodiment using PbSe quantum dots as photoconductors. Figure 7 shows an embodiment using organic materials as the photoconductors. Figure 8 shows an embodiment using a photoconductor as a light sensor.

Detailed Disclosure

Embodiments of the subject invention relate to a method and apparatus for infrared

(IR) detection. A specific embodiment utilizes organic layers to produce a phototransistor for the detection of IR radiation. The wavelength range of the IR detector can be modified by incorporating materials sensitive to photons of different wavelengths. In a specific embodiment, quantum dots of materials sensitive to photons of different wavelengths than the

host organic material of the absorbing layer of the phototransistor can be incorporated into the absorbing layer so as to enhance the absorption of photons having wavelengths associated with the material of the quantum dots.

In another embodiment, a photoconductor structure can be used instead of a phototransistor. In one embodiment, the photoconductor can incorporate PbSe or PbS quantum dots. In another embodiment, the photoconductor can incorporate organic materials.

Specific embodiments also involve displaying a detected IR image to a user. In a specific embodiment, organic materials can be used to create an organic light-emitting device. Additional material that emits at different wavelengths can be added to the light- emitting layer. In a specific embodiment, quantum dots of materials associated with emission of photons of different wavelengths than the host organic material of the emission layer can be incorporated into the emission layer to enhance the output display of the organic light- emitting device to the user. In a preferred embodiment, the IR detection is accomplished with a phototransistor and the displaying of the detected IR image is accomplished with an organic light-emitting device such as an organic light-emitting diode (OLED). In a more preferred embodiment, the phototransistor and OLED are in series.

Embodiments of the subject invention pertain to a method and apparatus for night vision. In an embodiment, a night vision device can be accomplished by the deposition of layers of organic thin films. Embodiments of the subject device can operate at low operating voltages, such as 10-15 V. In addition, the cost of manufacturing specific embodiments of the subject device can be lower than the cost of manufacturing conventional night vision systems. In an embodiment of the subject night vision device an organic phototransistor can be in series with an organic light-emitting device, such as an organic light-emitting diode (OLED). Preferably, electrodes that are transparent to infrared light are used to allow IR radiation to enter the phototransistor. A schematic diagram of an embodiment of an IR sensor/detector, an embodiment of an IR sensor-display combination, and a circuit model for the IR sensor-display combination are shown in Figure 1. A PNP bipolar phototransistor created using layers of organic material is shown on the left of Figure 1. Here, CuPc is the n- layer and PTCBI is the p-layer. Although the curved arrow symbolizing light (absorbing IR and emitting green) are shown pointing to the absorption layer and emission layer, respectively, the IR light enters from the top and the visible light is emitted from the bottom of the device shown in Figure 1. In the middle of Figure 1, the integration of the

phototransistor shown on the left with an OLED is shown. IR images can be incident on the top of the electrode layer (NiO) of the phototransistor and pass through the CuPc layer and into the absorption layer (PTCBI).

Upon photoexcitation with infrared light, charge carriers are generated in the phototransistor and injected into the OLED, which then generates photons in the visible range. Because of the low conductivity of organic thin films, the electric field will be confined within the photoexcited area and visible photons will be generated within the excited area. As a result, if a broad area device is exposed to an infrared image, a visible image will be generated. Preferably, an electrode transparent to visible light is used at the bottom, where the output image is emitted. In the embodiment shown, ITO is used as an electrode, which is transparent to visible light. Other materials can also be used. A circuit diagram of the integrated device shown in the middle is shown on the right side of Figure 1. In a specific embodiment, no electronics are required to operate the device. In an embodiment, the operating voltages of the phototransistor and the light-emitting device are less than 10 V, such that the total operating voltages can be less than 20 V. This device can be made very light weight.

In an embodiment, glass can be used as a substrate for fabrication. The entire phototransistor and OLED combination can be very thin, for example, less than lμm. The glass substrate with the thin layer can then be made part of night vision goggles where the thin layer is positioned to receive an IR image and a user is positioned to see the visible image emitted from the glass, or plastic, substrate.

Figure 2 shows the PNP bipolar transistor of Figure 1 and an NPN phototransistor, which can also be utilized in accordance with the subject invention.

The fabrication procedure for a specific embodiment of the subject IR detector- display combination will now be described. This fabrication procedure does not require any patterning. Other fabrication techniques, as well as other materials, as would be apparent to one skilled in the art having the benefit of the subject disclosure, can also be utilized in accordance with the subject invention. Devices are grown on a glass substrate or plastic substrate precoated with a 100 nm thick layer of indium-tin-oxide having a sheet resistance of 20 ohms/square. Substrates are degreased with solvents and then cleaned by exposure to oxygen plasma and UV-ozone ambient. All layers are vacuum deposited grown in succession without breaking the vacuum. In the first deposition step on top of the indium-tin-oxide (ITO) layer, to fabricate the integrated PNP phototransistor and OLED shown in the middle

of Figure 1, a 10-nm -thick CuPc is deposited as a hole injection layer. A 50 nm-thick NPD layer is then grown and acts as a hole transport layer. Next, a 60 nm-thick Alq3 emissive layer is deposited. A LiF (2 nm)/NiO (IOnm) charge generation layer is then deposited. This results in an OLED. To fabricate the phototransistor on the top of the light emitting device, a 40 nm thick CuPc layer, a 50 nm thick PTCBI layer, a 40 nm thick CuPc layer, and a 1000 nm NiO layer are then deposited.

In another specific embodiment, referring to Figure 3, the PTCBI layer of the phototransistor is replaced with a PbS or PbSe quantum dot layer. The PbS or PbSe absorbs photons of different wavelengths than the PTCBI layer. As an example, a PTCBI layer can be created that absorbs photons up to wavelengths of about 1 μm and a PbSe quantum dot layer, or PbS quantum dot layer, can be created that also absorbs photons having wavelengths in the range of about 1 μm to about 3 μm, so as to expand to wavelength range for detection. Other wavelength ranges can be accomplished by proper selection of the material in the absorption layer. In a further specific embodiment, referring to Figure 4, the 60 nm Alq3 layer of the light emitting device from Figure 1 or Figure 3 is replaced with a 50 nm Alq3 layer and a CdSe quantum dot layer. The material for the quantum dot layer can facilitate emission of light at wavelengths different from the light emitted by the Alq3 layer. Accordingly, other materials can also be utilized in accordance with the subject invention. Figure 5 shows structures of materials that can be utilized with embodiments of the subject invention. Shown in Figure 5 are structures for tris-(8-hydroxyquinoline) aluminum (Alq3), 4-4'-bis[N-(l-naphthyl)-N-phenyl-amino]biphenyl (NPD), copper phthalocyanine (CuPc), and perylene-3,4!8,10-tetra-carboxylic-diimide-di~2,6-isopropy~p henyl (PTCDI).

Although exemplary embodiments directed to a phototransistor and phototransistor/OLED combination fabricated primarily from organic material layers have been described, additional embodiments can utilize inorganic materials for the phototransistor and/or the light emitting device. Examples of inorganic materials that can be used to fabricate phototransistors and/or light emitting device in accordance with the subject invention include, but are not limited to, amorphous silicon, germanium, and diamond-like carbon. Thin film amorphous silicon could have PbSe or PbS to absorb IR. An inorganic OLED can use ZnO to emit visible light. The use of inorganic materials in the absorption layer can allow detection of IR with wavelengths in the range of about 1 μm to 4 μm. These materials and the techniques to fabricate phototransistors and/or OLED 's with structures

similar to those shown in Figures 1, 2, 3, and 4 are known to those skilled in the art. In this way, an inorganic phototransistor can be incorporated with an organic OLED and an organic phototransistor can be incorporated with an inorganic OLED.

Embodiments of the present invention can incorporate a photoconductor. In specific embodiments, a photoconductor can replace the phototransistor described in the above embodiments. Figure 6 shows a photoconductor device incorporating PbSe quantum dots. The PbSe quantum dots can be used to sense photons with wavelengths between 1 μm to 3 μm. The photoconductor structure can be formed of photoconductive material arranged between two electrodes. In one embodiment, one electrode can be formed of gold (Au) and the second electrode can be formed of ITO. In an embodiment, PbS quantum dots can be used in the place of the PbSe quantum dot layer. In operation, carriers can be photoexcited in the quantum dot (QD) layer through the absorption of IR rays. The carriers can travel to an OLED element to emit, for example, green light. In particular, electrons may be injected into an emissive layer of the OLED element and recombine with holes to give off light. In the embodiment shown in Figure 6, the photoconductor can be formed on an

OLED element. The OLED element can be formed on a glass substrate and can incorporate an ITO layer formed on the substrate, a CuPc layer formed on the ITO layer to act as a hole transport layer, a NPD layer formed on the CuPc layer to act as a hole transport layer, an AIq layer formed on the NPD layer, and a LiF/NiO layer for charge generation formed on the AIq layer. The photoconductor can be formed on the LiF/NiO layer by depositing a gold layer on the LiF/NiO layer, forming a photoconductive material layer on the gold layer, and forming an ITO layer on the photoconductive material layer.

Figure 7 shows a photoconductor device incorporating organic materials. Referring to Figure 7, one of the electrodes for the photoconductor can be eliminated when incorporated with an OLED element. In particular, the photoconductive material can be in direct contact with a hole transporting layer of an OLED. In an embodiment, titanyl phthalocyanine (TiOPc) can be used as the photoconductive material of a photoconductor device. The TiOPc can respond to IR rays because TiOPc absorbs wavelengths at 0.8 μm. The OLED element can be formed on a glass substrate and can include an ITO layer formed on the substrate, a LiF/NiO layer formed on the ITO layer, an AIq layer formed on the LiF/NiO layer and a NPD layer formed on the AIq Layer. The photoconductive material can be formed directly on the NPD layer without an intervening electrode.

Figure 8 shows an embodiment incorporating a photoconductor as the light sensor. A photoconductor can have very large gain or amplification and is ideal to amplify the signal.

The photoconductor device includes two layers, a charge transport layer and a sensitizer.

NPD can be used as a charge transport layer and PbSe, PbS, and/or InAs quantum dots can be utilized for photon absorption.

In operation, carriers can be photoexcited in the TiOPc layer. The carriers can travel to the OLED element to emit, for example, green light. In particular, holes can be injected into the NPD layer to recombine with electrons and give off light.

In embodiments of the present invention, the gain in photoconductors can be as large as 100,000.

For embodiments incorporating photoconductors instead of phototransistors, fabrication may involve less process steps due to embodiments of photoconductors being single layer devices instead of a three-layer NPN or PNP structure.

All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.