WO2006097129A1

WO2006097129A1 - Planar image sensor

Info

Publication number: WO2006097129A1
Application number: PCT/EP2005/002871
Authority: WO
Inventors: Uwe Vogel; Michael Scholles; Bernd Richter; Uwe Schelinski
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2005-03-17
Filing date: 2005-03-17
Publication date: 2006-09-21

Abstract

A planar image sensor suitable as a cheap planar image X-ray detector comprises an image detector layer arrangement (6) with a laterally unstructured image detector layer (7). The image sensor further comprises an OLED matrix (12) running over the image detector layer arrangement (6) with a number of optionally controlled OLEDs (13) for point light stimulation of the image detector layer (7).

Description

Flat image sensor

description

The present invention is concerned with a flat image sensor. In particular, the present invention is concerned with a large area flat panel x-ray detector for use in medical imaging equipment.

Large-area flat-panel x-ray detectors are finding increasing use in devices of diagnostic imaging in medicine, but also material inspection, eg. In the electronics and semiconductor industries. Alternatively, small-format CCD or CMOS detectors are used, which detect X-ray radiation converted into visible light by means of a reducing projection optics.

Within the framework of medical imaging diagnostics, the new detectors are to be used both in radiological diagnostics (X-rays, for example mammography) and in the verification of the patient's situation in radiotherapy. Furthermore, they will be incorporated into mobile C-arm X-ray equipment, which is an indispensable part of interventional procedures in cardiology (balloon dilatation), orthopedics, surgery and in particular accident surgery. Finally, this technology enables a whole new generation of reasonably priced, high-speed, high-resolution Cone-Beam CT devices.

In radiological diagnostics, as well as in surgery and radiotherapy, there is an extreme worldwide need for x-ray detectors, which include the digital acquisition of x-ray images and their further processing and evaluation in the Computer enable. Detectors for digital radiography are described, for example, in DE 19633580 A. Of particular importance is the high sensitivity of these ^■ detectors to minimize radiation-related risks for patients. Such X-ray detectors will replace the conventional X-ray films in the medium term if they are on the one hand large enough, ie have a dimension of about 40 cm x 40 cm, and have a sufficiently good spatial and brightness resolution and on the other hand are inexpensive to manufacture.

At present commercial image storage plates or image storage foils are used, which are designed as unstructured layer arrangement as a solid, this solid state layer arrangement has the property of storing an X-ray image in a corresponding charge distribution, which under selective light excitation according to the principle of stimulated luminescence in a suitably constructed Device is read out digitally. An example of a solid state layer arrangement is shown in DE 3312264 A1. A flexible form of such an unstructured layer arrangement is described in DE 19859880 A1 and also in DE 69601603 T2. With regard to the technique of reading out the charge distribution by means of stimulated luminescence, reference is made, for example, to DE 19506908 C2 and to US Pat. No. 3,859,527 A.

^' Alternative to the' described ^' image storage disks or ^•

Bildspeicherfόlien currently commercially so-called. Active flat-panel detectors are used, which are designed as rnatrixförmige, laterally structured sensor arrays, which usually pixel-like photodetectors of amorphous silicon in combination with thin-film transistors for selective tive readout of ^• pixels. In this regard, reference is made to DE 10307752 A1, DE 69511292 T2 and to DO 2004/105449 A1.

Both detector types, ie the image storage disks or image storage films on the one hand and the active flat-panel detectors on the other hand, if necessary, combined with converter layers, which are also referred to as scintillators, if the detectors themselves are not directly applicable or not sensitive enough for X-radiation. In this case, the converter material or scintillator material converts the energy of the x-ray radiation into an electromagnetic radiation in that wavelength range in which the photodetector is sensitive. This is often the area of visible light.

In particular, the active Flachflächtetekoren meet the technical requirements for X-ray detectors in terms of local and brightness resolution largely. They even allow the recording of image sequences. However, for wide applications, these flat panel detectors are too costly, costing more than € 100,000 each. A major reason for the high cost of these detectors lies in the technological effort for their lateral structuring.

As a further active principle for the so-called. Unstructured image sensors "LSP" (laser scanned photo diode) is more recently the so-called. Became known, the area of a large- ^', unstructured PiN diode layer is formed within an existing on its surface brightness distribution to a corresponding modulation of the existing in the interior of the semiconductor structure elec- field leads. Bssi this "LSP" is the electric field, which reflects the brightness distribution, read out by point illumination with a light beam or laser beam of low intensity, whereby the device provides an electrical signal at its outer surface electrodes, which is a measure of the brightness of the original image is at the point hit by the light beam. With regard to these principles of action, reference is made to the following documents.

LSP image sensors based on SiC heterostructures; Vieira, M. / Fernandes, M./Fantoni, A./Louro, P./Vygranenko, Y./Black, R. / Schubert, M.B .; Applied Surface 184 (2001), pp. 471-478;

Vieira, M./Fernandes, M./Munins, J./Antunes, P.L./Macarico, Al / Schwarz, R. / Schubert, M.B. Sensors and Actuators ArPhysical, Äug 2001;

Tailored Laser Scanned Photodiodes (LSP) for Image Recognition Vieira, M./Fernandes, M./Louro, P./Vygranenko, Y./Black, R./Schubert, M., Materials Research Society Symposium Proceedings; San Francisco, CA; 2001; April; Symposium A (2001)

Large Area Carrier Transport and Photogeneration pin-Su / SiC Heterojunctions, Louro, P.Yygranenko, Y./Braun, R./Ferandes, M./Viera, M./Gloeckner, J./Schubert, M., Ma - terials Research Society Symposium Proceedings; San Francisco, CA; 2001; April; Symposium A (2001); Laser scanned photodiodes LSPs) for image sensing, Vieira, M./Ferrandes, -M./Vygranenko, Y./Louro, P./Brun, R./Schubert, M., Sensors and Actuators A; Physical, Apr. 2002

Bias-dependent photocurrent collection in p-I-n-Si: H / SiC: H heterojunction, P. Louro. - In: European Conference on solid state transducers;

Transducers '01 Eurosensors XV; ll ^th international confer- ence on solid - equipped Sensors and actuators (2002), pp 221-226.

In the case of this so-called "LSP", a two-dimensional image is obtained, as in the image memories, in that the light beam of the laser source scans the detector surface. A laser with a suitable deflection device is used as the laser source. "However, the" LSP "does not work as a frame buffer, but must be exposed during the entire image evaluation. The following publications

A-Sic: H / a-Si: H tandem photodiodes; a numerical simulation, Fantoni, A. / Fernandes, M./Louro, P./Rodrigues, I./Vieira, M. Sensors and Actuators A 113 (2004), p. 324-328;

Large area image sensing struct ^'ures based on a-SiC: H; a dynamic characterization; Fernandes, M. / Vieira, M. / Rodrigues, ^• I. / Martin, R .; Sensors and Actuators A 113 (2004), pp. 360-364;

Optical confinement and color separation in a double colo ^'ur laser scanned photo diode (D / CLSP); Vieira, M. / Fernandes,

RECTlFlED SHEET (RULE 91) ISA / EP M./Loura, P./Fantoni, A. / Rodigues, I .; Sensors and Actuators A114 (2004), pp. 219-223;

A non-pixel image reader for continuous image detection based on tandem heterostructures, Vieira, M./ Fernandes, M. / Fantoni, A. / Louro, P .; Sensors and Actuators A 115 (2004), pp. 191-195;

Novel structure for large area image sensing, Ferandes, M./Vieira, M./Munins, R .; Sensors and Actuators A115 (2004), pp. 357-361; and

Optoelectronic characterization of a SIC: H-stacked devices Louro, P./Fantoni, A. / Fernandes, M./Macarico, A./Braun, R./Vieira, M., Journal of Non-Crystalline Solids, June 2004;

report an improvement of these components such that, instead of the simple PiN diode structure, two P-type structures arranged one above the other form an unstructured image sensor, the one side of the PiN structure for exposure, that is to say the charge image and the other side is used to read the image by means of a scanning laser light beam.

US Pat. No. 4,954,706 A discloses an image sensor which comprises an unstructured photoconductive layer provided with a phosphor layer as a scintillator, the photoconductive layer being enclosed between strip-shaped electrodes which each have the same direction in a first direction. Under the photoconductive layer there is an excitation light source in the form of semiconductor LEDs, which is arranged in one-dimensional linear excitation

RECTlFIED SHEET (RULE 91) ISA / EP is divided, which run perpendicular to the E- lektrodenstreifen. By means of a complex selection circuit device, on the one hand, the strip-shaped electrodes and, on the other hand, the one-dimensional excitation light sources are activated in order to determine readout ranges of the sensor. Although this known image sensor allows high resolutions, but leads due to the discussed complex technology in large-sensor areas at unacceptable costs.

Based on this prior art, the present invention has the object to provide a large-scale implementable image sensor that can be produced with relatively low technological complexity and compared to the cost of marketable large-scale image sensors low cost.

This object is achieved by a flat image sensor according to claim 1.

The present invention is based on the finding that a particularly simple, technologically easily realizable structure of an image sensor is achieved by having an image detector layer arrangement comprising an unstructured image detector layer, wherein the image sensor further comprises an OLED matrix extending over the image detector layer arrangement, having a plurality of selectively controllable OLEDs for punctual light stimulation of the image detector layer. The stimulation of the laterally unstructured image detector layer can be implemented point by point in a manner that is easy to control without the need for the comparatively high constructional effort required for the "LSP" (laser scanned photodiode). todiode) is required. The object of the invention also avoids the complex control and technologically difficult implementation of line light sources in the form of semiconductor LED lines with complementary activation of vertically extending electrodes, as is required in the technology discussed above according to US Pat. No. 4,947,070.

The invention achieves a selective readout of a picture detector layer, which in itself is unstructured, with a low level of technological complexity and a low overall depth.

In complete departure from the prior art, the light stimulation of the image sensor according to the invention is carried out by an O-LED matrix, which can be applied by means of simple methods on commercially available, inexpensive ^' available Bilddetektorschichtanordnungen, which otherwise for reading by means of an applied laser beam according to the discussed "LSP ^λS technology, ie used.

Although the image sensor according to the invention is preferably used for the detection of images in X-ray diagnostics, but can also be used for other image captures, for example, images in the visible wavelength range.

According to a preferred embodiment, the electrodes are each in the form of a plurality of parallel to each other running and spaced apart and electrically insulated from each other electrode strips, the electrode strips of the two electrodes are perpendicular to each other. In the embodiment of the image detector layer as a charge storage layer, this electrode structure makes it possible to read out that partial charge from the charge storage layer, which is punctually stimulated with light by an optionally controlled OLED, with a signal / noise ratio which is increased compared to planar electrodes by means of readout circuits known per se, as also known for the so-called "LSP" (laser scanned pho - todiodes) were used.

Increased sensitivity to X-rays is achieved by arranging a scintillator layer on the image detector layer arrangement.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Show it:

1 is a schematic representation of a flat

X-ray detector with an inventive

Image sensor; and

Fig. 2 is a perspective view of a preferred electrode structure of the image sensor.

The flat-panel X-ray detector designated in its entirety by the reference numeral 1 comprises a flat image sensor 2 through which an image is taken, which images a radiation source 3 for X-ray radiation by irradiation of an object or patient 4 on the image sensor 2 ,

The two-dimensional image sensor 2 has on its main surface facing the object a scintillator layer 5, which serves in a manner known per se for converting the energy of the X-ray radiation into an electromagnetic radiation in which nigen wavelength range in which a to the scintillator 5 - adjacent image detector layer assembly 6 is sensitive. The image detector layer arrangement 6 has a laterally unstructured image detector layer 7.

A possible embodiment of such an image detector layer arrangement 6 is a laterally unstructured large-area P-i-N diode layer arrangement.

On both sides of the image detector layer arrangement 6, electrodes 8, 9 are arranged, which in the simplest case cover the entire area of the image detector layer arrangement 6 on its two main surfaces. A voltage drop across the electrodes 8, 9 is amplified by a voltage amplifier 10 whose output is connected to a control and data acquisition circuit 11.

On the side facing away from the scintillator layer 5 of the image detector layer arrangement 6, an OLED matrix 12 is arranged, which consists of a plurality of individually controllable, matrix-like arranged OLEDs 13. Each of the OLEDs 13 is individually selectively controllable by the control and data acquisition circuit 11. The OLED matrix 12 is formed on the surface of a substrate 14.

In principle, the electrodes can be 8, 9 running over the whole area on the ^'two main surfaces of the image detector layer arrangement. 6

However, an improved signal-to-noise ratio is achieved when the electrodes 8, 9 in the manner shown in Fig. 2 are each by a plurality of parallel to each other extending, spaced apart and electrically isolated from each other electrode strips 8a, 8b; 9a

9b, .... be formed. The electrode strips 8a, 8b, one electrode 8 are arranged perpendicular to the electrode strips 9a, 9b, the other electrode 9. Only those strip electrodes 8a, 8b, or

9a, 9b, to which a voltage is applied by activation of the locally added OLED 13 are used by a circuit (not shown) for the signal evaluation.

In contrast to the preferred embodiment described, the image sensor can also be designed without a scintillator layer 5 if it is used for evaluating images in the visible wavelength range or if the sensitivity of the sensor to the detected X-radiation is high enough even without a scintillator layer.

In a further departure from the described exemplary embodiment, the image detector layer arrangement can also be configured as a double P-i-N diode layer instead of as a P-i-N diode layer.

Any other laterally unstructured semiconductor layer arrangement is also possible, provided that it is suitable for storing a charge distribution corresponding to an image.

In the embodiment described above, the laterally unstructured image detector layer is formed by a photodiode layer and in particular by a PiN. Diode layer or formed by a double PiN diode layer.

However, commercially available image storage plates or image storage films may also be considered as laterally unstructured image detector layers, in which charge carriers corresponding to the captured image are trapped in a charge storage layer, the charge carriers being readable by local exposure to the OLEDs of the OLED matrix.

In the embodiment of the image detector layer as a charge storage layer, the charge stored in the charge storage layer can be read out according to the principle of stimulating luminescence on the basis of the punctual light stimulation effected by the actuated OLEDs 13. Here, a measurement of the emitted light takes place.

In designing the image detector layer as a charge storage layer, it is also possible to detect the charge stored in the charge storage layer by reading out a signal dropping across both sides of the charge storage layer, which corresponds to the charge carriers released by the punctual light stimulation.

Claims

claims

1. Flat image sensor with the following features:

an image detector layer assembly (6) having a laterally unstructured image detector layer (7); and

an OLED matrix (12) extending over the image detector layer arrangement (6) with a plurality of optionally controllable OLEDs (13) for selective light stimulation of the image detector layer (7).

2. A flat image sensor according to claim 1, wherein the image detector layer assembly (6) comprises a charge storage layer.

3. Flat image sensor according to claim 2, wherein the charge stored in the charge storage layer is read out on the basis of the triggered by the OLEDs (13) punctual light stimulation according to the principle of stimulated luminescence.

A flat image sensor according to claim 1 or 2, wherein the image detector layer device (6) is formed by an image memory disk or an image memory film.

5. A flat image sensor according to claim 2, wherein the

Image detector layer arrangement (6) has electrodes (8, 9) arranged on both sides of the image detector layer; and in which the charge stored in the charge storage layer is read out by a signal dropping across the electrodes (8, 9) which corresponds to the charge carriers released by the punctual light stimulation.

6. A planar image sensor according to claim 1, wherein the image detector layer arrangement (6) has a planar, laterally unstructured photodiode layer with electrodes (8, 9) arranged on both sides as the image detector layer.

A flat image sensor according to claim 6, wherein the photodiode layer is a P-i-N photodiode layer.

A flat image sensor according to claim 6, wherein the photodiode layer is a double P-i-N photodiode layer.

9. A flat image sensor according to any one of claims 5 to 8, wherein the two electrodes (8, 9) each having a plurality of mutually parallel, spaced-apart and electrically isolated from each other electrode strips (8a, 8b, 9a, 9b).

10. A flat image sensor according to claim 9, wherein the

Electrode strips (8a, 8b,) of the one electrode

(8) extend perpendicular to the electrode strips (9a, 9b) of the other electrode (9).

A flat image sensor according to any one of claims 1 to 10, comprising a scintillator layer (5) disposed on the image detector layer array.