Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K39/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic radiation-sensitive element covered by group H10K30/00
  • H10K39/30—Devices controlled by radiation
  • H10K39/32—Organic image sensors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K39/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic radiation-sensitive element covered by group H10K30/00
  • H10K39/30—Devices controlled by radiation
  • H10K39/36—Devices specially adapted for detecting X-ray radiation
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/10—Organic polymers or oligomers
  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
  • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/10—Organic polymers or oligomers
  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
  • H10K85/114—Poly-phenylenevinylene; Derivatives thereof
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/20—Carbon compounds, e.g. carbon nanotubes or fullerenes
  • H10K85/211—Fullerenes, e.g. C60

Definitions

• the invention relates to an organic pixelated flat detector with increased sensitivity.
• the commercially available flat-plate detectors combine a-Si thin-film transistors and a-Si PIN diodes. Especially because of the PIN diodes, these detectors are very expensive to manufacture, so expensive.
• Photodiodes based on organic semiconductor materials offer the possibility of producing pixelated flat detectors with high external quantum efficiencies (50 to 85%) in the visible region of the spectrum.
• the thin organic layer systems used in this case can be produced inexpensively with known production methods such as spin coating, doctor blades or printing methods and thus allow a price advantage, especially for large area flat panel detectors. From US 2003/0025084, for example, a promising application of such organic flat-plate detectors, e.g. in medical image recognition as X-ray flat detectors, since the light of a scintillator is typically detected on relatively large areas of at least a few centimeters.
• an inorganic-based flat detector which discloses an inorganic pin photodiode, for example comprising a photoactive layer comprising an amorphous selenium, which is connected to an amplifier circuit comprising a plurality of thin-film transistors.
• the disadvantage of this is, in addition to the Using the expensive PIN diode also requires an additional resistor Ri oad in each column.
• US Pat. No. 6,600,160 B2 discloses a conventional flat-diode detector based on PIN diodes, which, in turn, apart from the considerable disadvantage that the photosensitive elements, that is to say the PIN diodes, are uneconomical to produce, has a circuit which only has one amplifier but shows an arrangement in which an additional precise current source is required for each column to be read.
• the object of the present invention is to overcome the disadvantages of the prior art and to provide cost-effective flat detectors available.
• the present invention is a pixelated flat detector with rows and columns of pixels, each comprising at least one organic photodiode, a reset transistor, a gain transistor and a read transistor.
• pixel is understood to mean the present unit comprising a photodiode, transistors and associated lines.
• the pixel includes the cost-effectively producible organic photodiode, which fundamentally differentiates the subject of the invention from the known flat detectors.
• the pixelated flat detector according to the invention comprises large active matrix detector arrays with over 200, for example with over 1000 lines.
• the noise contributions of the read-out electronics also called “amplifier noise”
• the feed lines thermal noise on the data line and extrinsic
• Noise due to capacitive coupling with external voltage sources is dominant in comparison to the noise contributions of the individual pixels.
• the invention is provided to effectively reduce these noise contributions by a preamplification of each individual pixel, that is to say an amplification of the resulting signal already at the pixel level, and thus make it possible to use organic photodiodes in the flat detector industry.
• This requires two additional transistors per pixel: a gain transistor and a reset transistor.
• each pixel according to the invention may be constructed on both an inorganic and organic basis.
• inorganic based transistors is possible because, among other things, thin-film transistors made of amorphous silicon are technologically widely developed by the flat-panel display industry and therefore can be obtained inexpensively.
• the organic diode is connected to a common supply voltage Vi for all pixels. When illuminated, this leads to a change in the voltage Vsignai / which is reset to the voltage V2 before each lighting cycle with a voltage pulse V rese t on the gate of the reset transistor.
• the organic photodiode is connected directly to the amplifier transistor and the reset transistor.
• the invention is in the pixel of the readout transistor with the amplifier transistor connected, which in turn is connected to the reset transistor and the photodiode.
• organic in connection with the components diode and / or transistor is meant here in general and includes the meaning of the English "plastics".
• other compounds and polymers which are not necessarily carbon-containing and also include organometallic materials, all types of blends and polymer blends or mixtures of nonpolymeric compounds such as oligomers and monomers should be included.
• organometallic materials all types of blends and polymer blends or mixtures of nonpolymeric compounds such as oligomers and monomers should be included.
• silicones or other common plastics ie all materials except the inorganic semiconductors, which usually make up the classical p-i-n diodes.
• An organic photodiode according to the invention comprises at least the layers substrate, lower electrode, photoactive layer, upper electrode and optionally an encapsulation.
• the substrate can be made of a glass in the
• Thickness range of 50 microns to 2mm be created from a flexible plastic or metal foil or other conventional material. It is advantageous if, in addition to the organic photodiode, further components, such as transistors, are arranged on the substrate. The arrangement on a substrate shortens lines, simplifies production steps and generally saves costs.
• the pre-amplification of the organic photodiode pixels according to the invention does not preclude the flat-plate detector from having further means for amplifying the signal.
• signal amplifying resistors, capacitors, other diodes and / or transistors could be used.
• Figure 1 shows the scheme of a circuit of an active
• FIG. 2 shows the diagram of an array of two rows and two columns of a flat detector
• FIG. 3 shows an active organic pixel in plan view
• FIG. 4 shows the cross section through an active pixel marked in FIG.
• FIG. 1 shows an actively amplifying pixel 1 according to the present invention.
• Each pixel 1 contains an organic photodiode 2, a reset transistor 3, a gain transistor 4 and a read transistor 5.
• the organic photodiode 2 is connected to a, in the example shown here for all pixels common, supply voltage Vl. It leads to a change in the voltage V signa i when lighting, which is reset before each lighting cycle with a voltage pulse V rese t on the gate 6 of the reset transistor 3 to the voltage V2.
• the signal is read out via the amplifier transistor 4, on whose drain side 7 the voltage V3 is present and whose source side 8 is connected via the read transistor 5 to the data line 9 and finally via this to the readout electronics.
• the supply voltages V2 and V3 are also common to all pixels. They can be at the same voltage level and connected via a common line. For an optimization of the signal amplification, however, it is advantageous to apply different voltages V2 and V3 via two separate lines.
• the photodiode is connected directly to the gate contact of the amplifier transistor and the source contact of the reset transistor.
• the drain contact of the readout Transistor 5 is connected to the source contact 8 of the amplifier transistor 4, the latter in turn via its gate to the reset transistor 3 and the photodiode. 2
• Exemplary voltage values are + 15V for Vl, + 10V for V2 and + 20V for V3.
• the voltages Vreset and Vread form pulsed signals which, for example, are switched between the values -5V (OFF) and + 15V (ON).
• FIG. 2 schematically shows the circuit for an array of several active pixels 1 as shown in FIG. Per line are two drivers 10, 11 for the pulsed
• each pixel is connected to the common supply lines for V1, V2 and V3, in this example.
• the connection for the supply voltage Vl here is, for example, a full-surface electrode that overlaps with the entire array, and is not shown in the figure.
• the common supply voltages V2 and V3 are summarized here, for example, each column by column, wherein the individual strands are combined at the edge of the array in each case to a common connection. In principle, it is also possible to combine these strands first line by line and connect accordingly to the right edge with a supply line. It is also possible to construct the supply voltage Vl differently than shown.
• the supply voltages V2 and / or V3 can be connected for all pixels, as shown in FIG. 2, but they can also be designed for individual pixels.
• the potential of V2 may be equal or unequal to that of V3.
• FIG. 3 schematically shows an active organic pixel in plan view
• FIG. 4 shows a cross section through the active organic pixel at the location shown in FIG.
• the power supplies for V2 and V3 are combined in a vertical line, so these two potentials are identical here.
• the two potentials V2 and V3 are unequal.
• the pixel anode 14 overlaps with the reset thin-film transistor 3 (TFT) and the amplifier thin-film transistor 4 (TFT).
• TFT reset thin-film transistor 3
• TFT amplifier thin-film transistor 4
• gate 13 and source / drain 15 can be seen. This increases the full factor significantly over a design without overlap between anode and transistors.
• the effective full factor of an organic photodiode pixel in this case is determined by the area of the pixel anode 14 plus a surrounding feed area of a few ⁇ m.
• an additional overlap with the readout transistor 5 is possible, which, however, brings with it the disadvantage of additional parasitic capacitances.
• a flat detector overlaps according to an exemplary embodiment, the patterned electrode of the organic photodiode with the reset transistor and / or with the amplifier transistor and / or with the read-out transistor.
• the organic semiconductor layer is full-flattened.
• the organic semiconductor layer is structured on the pixel level.
• both the organic semiconductor layer 16 and the common (here semitransparent) cathode 18 are full-surface and unstructured on all pixels of the array.
• the organic semiconductor 16 can also be structured on the geometry of the individual pixel anodes.
• the upper electrode 18 is always connected, at a potential Vl.
• the function of the pixel anode 14 and pixel cathode 18 can also be exchanged with respect to the example in FIG. 4, only the electrode connected to the amplifier and reset transistor is structured into individual pixels and the other electrode is connected in each case.
• the organic semiconductor layer 16 may comprise a plurality of organic sublayers, and additional inorganic barrier layers may be applied above and / or below the organic layers.
• first passivation SiNx or SiOxNy, between 100 and 500 nm - a-Si: between 30 and 300 nm (partially doped)
• Source / drain metal Cr or Al, between 50 and 500 nm
• SiNx, SiOxNy or organic photoresists between 100 and 500 nm
• Typical materials for organic transistors conductive: polymers based on polyaniline, semiconducting polymers based on polythiophene and insulators called polymers based on polyethylene.
• the layer thicknesses are different depending on the transistor structure, usually in thin-film technology.
• Typical materials and layer thicknesses of organic diodes - Pixel anode: Au, Pd, Pt, ITO between 20 and 200 nm
• Semitransparent cathode first layer of Ba, Ca, Mg, LiF or CsF between 1 and 10 nm and optionally a cover layer of Ag, Al or ITO with a layer thickness between 3 and 30 nm.
• an encapsulation e.g., glass cap or thin film encapsulation.
• the thin-film transistors can be realized as organic field-effect transistors (OFETs). This could also be cheaper for the transistors
• the advantage of the actively amplified organic detector array according to the invention is a reduction in the weight of the noise contributions that occur in the data line and in the amplifier. The effect of this reduction on the total noise is the higher the larger the array.
• the number of lines is typically between 1000 and 3000.
• the above-mentioned noise contributions after the pixel result in a proportion of typically 40-90% of the total noise.
• the effect of noise contributions is reduced by using actively amplified pixels by amplifying the signal even before the occurrence of certain noise contributions.
• the noise is not a total but the early amplification significantly increases the signal-to-noise ratio and the sensitivity of the detector.
• the degree of improvement in the signal-to-noise ratio depends on the gain G of the enhancing pixel.
• the gain indicates the ratio of the photo-charges generated in the pixel to the amount of charge at the output amplifier. He is given by the following formula:
• g is the transconductance of the
• Amplification transistor t the sampling time to read a pixel and C the pixel capacity.
• Typical values for these quantities when using a-Si transistors are:
• C 1 to 5 pF (with a pixel pitch between 80 ⁇ m and 200 ⁇ m).
• Typical gain factors are between 3 and 30.
• Simulations show that with a gain factor of 10 for an organic detector array with 150 ⁇ m pixel pitch, 20 ⁇ s read-out time and 4 pF pixel capacitance, the signal-to-noise ratio can be improved by a factor of 2 to 3 (compared to a pixel without amplification , only with a simple readout transistor).
• the smallest detectable signal is determined by the total noise related to the input of the pixel amplifier.
• this input noise value for an array of 1000 ⁇ 1000 pixels can be reduced to 1200 electrons according to simulations of 2000 electrons. The factor gets bigger for larger ones Arrays.
• an input noise value of below about 1500 electrons individual X-ray quanta can be detected with an X-ray detector.
• the improvement according to the present invention could thus enable the commercial use of organic photodiodes in X-ray flat detectors for low dose ranges.
• the invention relates to an organic pixelated

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• 2005
  • 2005-11-17 DE DE102005055278A patent/DE102005055278B4/de active Active
• 2006
  • 2006-11-09 CN CN2006800513059A patent/CN101361188B/zh active Active
  • 2006-11-09 WO PCT/EP2006/068279 patent/WO2007057340A1/de active Application Filing
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