CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage application under 35 U.S.C. § 371 of International Application PCT/NL2018/050411 (published as WO 2019/004823 A1), filed Jun. 26, 2018, which claims the benefit of priority to Application EP 17177873.1, filed Jun. 26, 2017. Benefit of the filing date of these prior applications is hereby claimed. Each of these prior applications is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a photodetector array.

The invention further relates to a method of manufacturing the same.

The invention still further relates to an imaging device including such a photodetector array.

Related Art

Thin film photodetector based imagers have the potential to be very thin, light and flexible. Moreover, a substantial reduction in production cost can be achieved, in particular for organic photodetector technology, as this allows relatively simple deposition and processing methods. Additional cost savings are achieved in that a fine-pitch patterning of the organic photodetector film and its top electrode in a large-area image sensor can be avoided. This may lead to a significant cost-savings compared to a-Si diodes.

A disadvantage of this process simplification is its vulnerability to fatal failure and defects. As the photodiode is now a large diode and consists of a very thin (normally less than 500 nm) active layer between the anode and the cathode electrode, abrupt failure during operation is one of the main reliability and yield issues. Tiny defective points are hardly avoidable even in the controlled cleanrooms. Some of these defects can cause abrupt electrical short and/or failure of a large part of the detector. Leakage channels formed around these defective sites may cause heat generation and this enhances the current density around the sites. As the resistivity of the site is lowered, current of the whole detector is concentrated to the site, lowering the sensitivity of the whole panel. Or, the defect causes direct electrical shorts between the defective site and the readout electronics, damaging the (ultra-sensitive) peripheral silicon charge sense amplifiers.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a photodetector array wherein this disadvantage is at least mitigated. It is a further object of the invention to provide a method of manufacturing such a photodetector array.

According to a first aspect of the invention, a photodetector array is provided that comprises a plurality of pixels between a supply line and a common electrode. Respective pixels comprise a photon radiation sensitive element arranged in a series connection with a switching element. The series connection further includes a resistive element.

In the inadvertent case that a photodiode in the photodetector array contains a defect and this happens to cause an electrical short of the photodiode, the current of the pixel containing this photodiode is limited to the level designed by the thin-film resistor and therewith at least mitigates damage that could result otherwise result to surrounding pixels.

In an embodiment the resistive element has a resistive value in the range of 0.05 to 0.2 times a normal resistive value of the switching element in its conductive state. Therewith not only a risk of damage is mitigated, but additionally it is achieved that a potential defect of a photodiode of a pixel affects performance of the neighboring pixels. Minor changes in performance could still be compensated by image processing methods applied to the retrieved image signals. Image processing methods may further be applied to estimate a correct value for an image signal obtained from a pixel with a defect photodiode.

The normal resistive value of the switching element in its conductive state is defined as the resistive value it is designed to have in its conductive state. In view of the fact that in practice at least a majority of the switching elements will perform as designed, the normal resistive value is approximately equal to the average value or the median value of the resistive values of the switching elements in their conductive state.

In an embodiment of the photodetector array according the first aspect, the resistive element is a thin film resistor. This is advantageous in particular if it desired that the photodetector array has a small thickness. Various options are available to provide a thin film resistor for this purpose.

For example, in an embodiment, each thin-film resistor is provided in a vertical interconnect area of each photon radiation sensitive element. In particular this may be achieved in that a surface of a connector for electrically connecting the photon radiation sensitive element with the switching element is oxidized in the vertical interconnect area.

In another embodiment a controllable channel of the switching element and the thin-film resistor respectively are formed in a first and a second region of a continuous portion of a layer of semiconductor material and wherein these regions are mutually differently doped to provide that a resistive value of the first region has a resistive value that is higher than a resistive value of the second region in a conductive state of the switching element, and lower than a resistive value of the second region in a non-conductive state of the switching element.

In again another embodiment the resistive element is formed as a portion with a restricted cross-section in an electrically conductive element in said series connection. The restricted cross-section may for example be a restricted cross-section of a via through an insulating layer. A higher resistive value can be obtained with a higher value for the thickness of the insulating layer or a lower value for the cross-sectional area. A lower resistive value can be obtained with a lower value for the thickness or a higher value for the cross-sectional area. Alternatively the restricted cross-section may be obtained as a restriction of a width of a conducting line in the series connection. A higher resistive value can be obtained with a higher value for a length of the restriction or a lower value for a width of the restriction. A lower resistive value can be obtained with a lower value for the length or a higher value for the width. Instead of modifying a width, alternatively a thickness of the conducting line may be modified, or a combination of such modifications is possible. In practice it is however easier to modify a width than a thickness.

In an embodiment, the photon radiation sensitive elements include a photon radiation sensitive layer of an organic material.

In an embodiment the photon radiation sensitive elements are sensitive for X-ray radiation.

According to a second aspect of the invention, an imaging device is provided. The imaging device comprises a photodetector array according to the first aspect for example in one of the embodiments presented above. Therein the supply line of the photodetector array is one of a plurality of supply lines and a respective plurality of pixels is coupled between each supply line and the common electrode. More in particular the plurality of supply lines are column lines driven by a column driver. The imaging device further comprises a plurality of row lines driven by a row driver and a respective pixel of each plurality of pixels has a control electrode of their switching element coupled to a respective one of the row lines.

According to a third aspect of the invention, a method of manufacturing a photodetector array according to the first aspect is provided.

The method of manufacturing an organic photodetector array, comprises the steps of providing the substrate, providing a first stack of layers, and providing a second stack of layers as defined below.

The substrate that is provided may optionally include an insulating layer, dependent on the material used for the substrate and user requirements.

In providing the first stack of layers at least one supply line is formed as well as a plurality of switching elements forming a respective controllable electrically conductive channel between the at least one supply line and respective electric contacts. Also the first stack of layers forms a plurality of control lines for controlling respective ones of the plurality of switching elements to control an electrical connection between the at least one supply line and the respective electric contacts.

In providing the second stack of layers, comprising at least a photon radiation sensitive layer, respective photon radiation sensitive zones are defined that are electrically connected to respective ones of the electric contacts at a first side of the at least a photon radiation sensitive layer. Providing the second stack of layers further includes providing a transparent electrically conductive layer that forms a common electrode on a second side of the at least a photon radiation sensitive layer opposite the first side.

In the method of manufacturing according to the third aspect, a respective controllable electrically conductive path is formed between the at least one supply line and the common electrode via a respective switching element and a respective photon radiation sensitive zone. In the method of manufacturing according to the third aspect these controllable electrically conductive paths are provided with a respective series resistance.

In an exemplary embodiment the method comprises, subsequent to providing the first stack of layers and before providing the second stack of layers the additional step of providing a first intermediary patterned layer of an insulating material that defines respective openings towards the respective contacts, as well as the additional step of forming a respective series resistance for the controllable electrically conductive paths by applying a surface treatment to the respective contacts within said openings. When providing the second stack of layers a first layer of the second stack protrudes into the respective openings to form an electric contact with the respective contacts exposed therein.

The surface treatment may include an oxidization step, for example including exposure of the exposed contacts to a plasma. Alternatively, the surface treatment may include the formation of a self assembled monolayer on top of the exposed respective contacts.

In another exemplary embodiment the method comprises subsequent to providing the first stack of layers and before providing the second stack of layers providing a first and a third intermediary patterned layers of an insulating material and providing a second intermediary patterned layer of an electrically conductive material.

The first intermediary patterned layer of an insulating material defines respective openings towards said respective contacts.

When providing the second intermediary patterned layer of an electrically conductive material the electrically conductive material is allowed to penetrate the openings and to contact the respective contacts within the openings. Therewith the electrically conductive material of the second intermediary patterned layer in the openings forms a respective series resistance for the controllable electrically conductive paths determined by the thickness of the first intermediary patterned layer and the cross-sectional area of the openings.

The third intermediary patterned layer of an insulating material is provided with second openings extending towards the second intermediary patterned layer. When providing the second stack of layers comprising a first layer of the second stack protrudes into the second openings to form respective electric contacts with the second intermediary patterned layer.

In another exemplary embodiment the method comprises before providing the second stack of layers the step of selectively modifying a target layer from the first stack of layers that forms the respective controllable electrically conductive channels. Therewith it is achieved that a respective portion of the layer that connects a respective controllable electrically conductive channel with the at least one supply line and/or a respective portion of said layer that connects a respective controllable electrically conductive channel with a respective electric contacts has a higher specific resistance as compared to that of the respective controllable electrically conductive channels. Such modification may be achieved in that the target layer is selectively doped, for example by at least one of oxidizing, reducing atmospheres, plasma treatment.

In another embodiment, wherein the common electrode is an anode of Indium Gallium Zinc Oxide the common electrode is selectively doped by one or more of H2 doping, deep UV illumination, Ca-based treatment outside these regions for a reduction of electrical resistance, to achieve that a local value of a resistance of the common electrode in regions defined by the photon radiation sensitive elements is higher than a value of a resistance of the common electrode outside these regions.

Any combination of the measures presented above may be applied. For example a protective resistive means in a path from the supply line via the switching element and via the photon radiation sensitive element to the common electrode may be provided by a combination of two or more resistive elements in various positions in the path, for example two or more of a resistive element at a position between the supply line and the switching element, at a position between the switching element and the photon radiation sensitive element and at a position between the photon radiation sensitive element and the common electrode.

