Patent Description:
A multipixel detector comprises several light sensitive pixels which detect light. Thus, a multipixel detector may detect an image projected on the multipixel detector. Each light sensitive pixel of the multipixel detector may be a photodiode. Thus, a multipixel detector may comprise an array of photodiodes. One type of photodiode is the thin film photodiode (TFPD). A TFPD comprises one or more thin film layers, wherein one of the thin film layers comprise photon absorbing material.

<NPL>) show a prior-art method for producing a multipixel detector.

It is an objective of the present inventive concept to provide a cost-efficient method for producing multipixel detectors. It is a further objective of the present inventive concept to facilitate production of high-quality multipixel detectors. It is a further objective of the present inventive concept to prevent lithographically related damage and/or etch related damage of thin film material during the production process. It is a further objective of the present inventive concept to facilitate production of multipixel detectors with few defective pixels, e.g. facilitate production of multipixel detectors with few electrically shortened pixels.

These and other objectives of the inventive concept are at least partly met by the invention as defined in the independent claim.

According to a first aspect there is provided a method for producing a multipixel detector, the method comprising:.

The first and second TFPD may herein respectively function as a first and second pixel of the multipixel detector.

According to the invention, the multipixel detector comprises thin film photodiodes. Such photodiodes can be produced in a cost-efficient manner, e.g. in a more cost-efficient manner than a thick film single crystalline pn-junctions. Thus, cost-efficient production of the multipixel detector is facilitated by the use of thin film photodiodes. Further, thin film photodiodes may be used in the short-wave infrared wavelength region, e.g. between <NUM> and <NUM>. Silicon based photodiodes may not work this wavelength region and devices comprising thick film single crystalline pn-junctions of other materials, such as e.g. InAs, may be expensive.

It is a realization that cost-efficient production is further facilitated when the production method for the multipixel detector is compatible with complementary metal-oxide-semiconductor (CMOS) production methods. CMOS production facilities are abundant.

The method provides a high-quality multiple pixel detector as damage to and/or degradation of the photon absorbing material during processing may be avoided or reduced. In a multipixel detector the photon absorbing material of each pixel should be separated from the photon absorbing material of the other pixels. It is a realization that if photon absorbing material for a thin film photodetector is lithographically patterned and etched to form separate pixels, as done in the prior art, the photon absorbing material may be damaged and/or degrade. The photon absorbing material may e.g. degrade due to lithographically related damage or due to etch related damage. Lithographically related damage may be damage caused by heat or radiation from the lithographic patterning process, e.g. heat or irradiation from UV-light exposure. Etch related damage may be formation of recombination centers on etched surfaces of the photon absorbing material. It is unfortunate that lithographic patterning and etching, which are commonly used in CMOS production, may cause damage to the photon absorbing material. However, it is a realization that when the first and second photon absorbing material are deposited in the respective first and second opening in the electrically insulating layer, the first and second photon absorbing material may be patterned and thereby separated by planarizing the electrically insulating layer, the first photon absorbing material and the second photon absorbing material.

The position and size of the respective first and second opening may define the position and size of the respective first and second TFPD. The position and size of the respective first and second opening (and thus of the first and second TFPD) may be defined when the first and second opening are formed. Forming the first and second opening may be done through lithographic patterning and etching of the electrically insulating layer. However, as some or all of the lithographic patterning and etching steps are performed before depositing photon absorbing material in the openings, degradation of the photon absorbing material may be avoided or reduced.

Further, damage to the photon absorbing material during formation of top electrodes may be avoided as a common top electrode is formed on top of the flat surface. Thus, instead of lithographic patterning and etching individual top electrodes, a common top electrode may be used.

Further, the method enables use of a common top electrode on top of the flat surface with a reduced risk of electrically shorted pixels, and thereby facilitates production of multipixel detectors with few defective pixels. The formation of such a common top electrode may ensure that there is a sufficient distance and electrical insulation between the top and bottom electrodes associated with a pixel to prevent short circuits which may result in a defective pixel.

Further, a common top electrode may result in a flat top surface. A flat top surface may be advantageous in many applications. For example, if the multipixel detector is used as part of a focal plane array, a flat top surface enables focal plane array processing on top of the multipixel detector.

Further, the method provides a high-quality multiple pixel detector as degradation of the photon absorbing material in the finished multipixel detector may be avoided or reduced. Depositing the photon absorbing materials in openings in the electrically insulating layer may protect the photon absorbing materials against coming in contact with the ambient air, e.g. against humidity in the ambient air. In the finished multipixel detector the photon absorbing materials may be completely surrounded by the electrically insulating layer, the bottom electrode and the common top electrode.

Due to the nature of the deposition process, the first and second photon absorbing material may be in contact with each other before the planarization. The planarization then forms a flat surface wherein the top surface of the second photon absorbing material is laterally separated from the top surface of the first photon absorbing material by the top surface of the electrically insulating layer, such that the first and second photon absorbing material are separated from each other. In other words, when photon absorbing material is deposited in an opening there may also be photon absorbing material deposited on the top surface of the electrically insulating layer, the photon absorbing material on the top surface of the electrically insulating layer may then be removed by the planarization. Planarizing the deposited electrically insulating layer, the deposited first photon absorbing material and the deposited second photon absorbing material may comprise chemical-mechanical polishing and/or grinding and/or fly-cutting.

The multipixel detector may comprise more than a first and a second TFPD. The multipixel detector may comprise an array of TFPDs. The array of TFPDs may be one-dimensional, e.g. comprise a single row of TFPDs, or two-dimensional, e.g. comprise rows and columns of TFPDs. The multipixel detector may be part of an imaging device.

As will be described further below, the first and second photon absorbing material may be, or comprise, the same material or different materials, e.g. materials with different absorption peak wavelengths. The first and second opening may be formed simultaneously or separately. The first and second photon absorbing material may be deposited simultaneously or separately.

The first and second photon absorbing materials may have the same thickness or different thicknesses. For example, the thickness of the first and/or second photon absorbing material may depend on the quantum efficiency of the photon absorbing material.

The common top electrode may be at least partially transparent to light.

Each pixel of the multipixel detector, e.g. each of the first and second pixel, may be configured to absorb a photon, such as a photon which has passed through a transparent common top electrode, by the photon absorbing material and thereby generate a photogenerated electron-hole pair in the photon absorbing material. Thus, each TFPD of the multipixel detector may be configured to absorb photons. Each TFPD of the multipixel detector may be configured to separate the electron and the hole of the photogenerated electron-hole pair and either:.

The first and second TFPD may each comprise a bottom charge carrier control layer between the photon absorbing material and the bottom electrode and/or a top charge carrier control layer between the photon absorbing material and the common top electrode, wherein each of the bottom and top charge carrier control layers of the first and second TFPD comprise at least one of: an electron transport layer, a hole transport layer, an electron blocking layer, a hole blocking layer, an electron injection layer, a hole injection layer.

The charge carrier control layers may be configured to facilitate separation of electrons and holes of photogenerated electron-hole pairs. This may be done by tuning (or bridging) the work function of the bottom electrode with respect to the work function of the photon absorbing material and/or tuning (or bridging) the work function of the common top electrode with respect to the work function of the photon absorbing material.

An electron transport layer may be a layer configured to enhance electron transport from the photon absorbing material to the adjacent electrode.

A hole transport layer may be a layer configured to enhance hole transport from the photon absorbing material to the adjacent electrode.

An electron blocking layer may be a layer configured to block electron transport from the photon absorbing material to the adjacent electrode.

A hole blocking layer may be a layer configured to block hole transport from the photon absorbing material to the adjacent electrode.

An electron injection layer may be a layer configured to enhance electron injection to the photon absorbing material.

A hole injection layer may be a layer configured to enhance hole injection to the photon absorbing material.

The bottom charge carrier control layer and top charge carrier control layer may be configured to promote transport of opposite types of charge carriers. As an example: if the bottom charge carrier control layer is an electron transport layer, the top charge carrier control layer may be a hole transport layer. As another example: if the bottom charge carrier control layer is a hole transport layer, the top charge carrier control layer may be an electron transport layer.

When the bottom charge carrier control layer is deposited in an opening through the electrically insulating layer, said bottom charge carrier control layer may not need to be lithographically patterned and etched. Thus, lithographically related damage and/or etch related damage to the bottom charge carrier control layer may be avoided or reduced, in analogy to the above discussion related to the photon absorbing material.

To illustrate, the first and second bottom electrodes may first be formed by depositing a layer of electrode material, e.g. metal. The layer of electrode material may then be patterned and etched into the first and second bottom electrodes after which the electrically insulating layer is deposited, the openings formed, and the bottom charge carrier control layer is deposited in an opening. Thus, the bottom charge carrier control layer may not need to be subjected to the patterning and etching of the layer of electrode material.

To cover side walls of an opening the bottom charge carrier control layer may be deposited with a conformal depositing technique.

When a bottom charge carrier control layer is deposited in an opening, the method may further comprise
forming an electrically insulating barrier on the flat surface formed by planarizing the deposited electrically insulating layer, the deposited first photon absorbing material and the deposited second photon absorbing material, the electrically insulating barrier covering a part of a bottom charge carrier control layer deposited in the first or second opening, wherein the covered part of the bottom charge carrier control layer lies within the flat surface.

Planarizing the deposited electrically insulating layer, the deposited first photon absorbing material and the deposited second photon absorbing material may also planarize parts of the bottom charge carrier control layer which have been deposited on the top surface of the electrically insulating layer and thereby remove said parts. However, after planarization there may be parts of the bottom charge carrier control layer within the flat surface. If a top charge carrier control layer or a common top electrode is deposited onto such parts of the bottom charge carrier control layer within the flat surface charge carriers may bypass the photon absorbing material and a defective pixel may be formed. Thus, it may be advantageous to provide an electrically insulating barrier covering the part of a bottom charge carrier control layer that lies within the flat surface. Thereby, defective pixels may be avoided or reduced. In particular, when depositing a common top electrode afterwards, the electrically insulating barrier may provide electrical insulation between the common top electrode and the bottom charge carrier control layer, such that defective pixels may be avoided or reduced.

The method may, as an alternative or addition to depositing a bottom charge carrier control layer in an opening, comprise:.

Thus, as an alternative to depositing a bottom charge carrier control layer in an opening, the bottom charge carrier control layer may be provided on a bottom electrode before depositing the electrically insulating layer. For example, the bottom charge carrier control layer may be deposited onto the layer of electrode material and patterned and etched together with the layer of electrode material. It is a realization that the bottom charge carrier control layer may not necessarily be as sensitive to lithographically related damage and/or etch related damage as the photon absorbing layer, at least in some situations. Further, depositing the bottom charge carrier control layer before depositing the electrically insulating layer may simplify the processing of the multipixel detector.

The method may further comprise forming a common top charge carrier control layer configured such that the common top electrode electrically connects to the top surfaces of the first and second photon absorbing materials in the flat surface via the common top charge carrier control layer, wherein the common top charge carrier control layer is formed after planarizing the deposited electrically insulating layer, the deposited first photon absorbing material and the deposited second photon absorbing material. Thus, damage to the photon absorbing material during formation of top charge carrier control layers may be avoided as a common top charge carrier control layer is formed on top of the flat surface. Thus, instead of lithographic patterning and etching individual top charge carrier control layers, a common top charge carrier control layer may be used.

It should be understood that in some situations individual top charge carrier control layers may be used.

It is a realization that some photon absorbing materials may be particularly sensitive to lithographically related damage and/or etch related damage. Such materials may be PbS quantum dots and/or InAs quantum dots and/or organic semiconductors. Thus, the first or second photon absorbing material may comprise PbS quantum dots, and/or InAs quantum dots and/or an organic semiconductor. In this case the advantages in terms of facilitating a high-quality of the multipixel detector may be particularly large.

As previously mentioned, the multipixel detector may comprise a CMOS circuit. For example, the bottom layer may comprise a complementary metal-oxide-semiconductor, CMOS, readout integrated circuit, wherein the CMOS readout integrated circuit comprises CMOS electronic circuits configured to convert an amount of charge carriers from the respective first and second TFPD into respective electrical signals when the multipixel detector is in operation.

As previously mentioned, the first and second photon absorbing material may be, or comprise, different materials, e.g. materials with different absorption peak wavelengths. Thus, an absorption peak wavelength of the first photon absorbing material is different from an absorption peak wavelength of the second photon absorbing material.

The absorption peak wavelength may be the wavelength at which photon absorption is strongest, e.g. the wavelength where the absorption coefficient of the photon absorbing material is largest.

When the first and second photon absorbing material have different absorption peak wavelengths they may absorb photon in different wavelength bands. Thus, the multipixel detector may be seen as a multispectral detector, also known as a multispectral sensor.

The multispectral detector may comprise more than a first and a second TFPD. The multispectral detector may be configured to absorb photons in more than two different wavelength bands, e.g. more than <NUM> different wavelength bands, or more than <NUM> different wavelength bands. The multispectral detector may comprise an array of TFPDs. The array of TFPDs may be one-dimensional, e.g. comprise a single row of TFPDs, or two-dimensional, e.g. comprise rows and columns of TFPDs. The multispectral detector may be a multispectral imaging device.

For a multispectral detector it may be advantageous to perform at least some of the processing of TFPDs with different photon absorbing materials separately. For example, it may be advantageous to at least partially form a TFPD with one photon absorbing material before starting to process a TFPD with another photon absorbing material. Thus, the TFPDs that are formed first may be subjected to many iterations of lithographic patterning and therefore subjected to heat and/or radiation from the lithographic patterning process many times in prior art methods. Therefore, the use of planarization and a common top contact to reduce the number of lithographic patterning processes the photon absorbing materials of the TFPDs are subjected to may be particularly advantageous for a multispectral detector.

The method may comprise configuring the multipixel detector such that the first bottom electrode is arranged at a first distance from the common top electrode and the second bottom electrode is arranged at a second distance from the common top electrode, wherein the second distance is smaller than the first distance. Different distances between the common top electrode and the respective first and second bottom electrode may be used to individually tune the absorption for the first and second TFPD. This may be useful when the first and second photon absorbing material are the same. It may be particularly useful when the first and second photon absorbing material are different, e.g. when the first and second photon absorbing material have different quantum efficiencies.

The method may comprise configuring the multipixel detector such that the first bottom electrode is arranged at a first distance from the common top electrode and the second bottom electrode is arranged at a second distance from the common top electrode, wherein the second distance is smaller than the first distance and wherein a quantum efficiency of the second photon absorbing material is larger than a quantum efficiency of the first photon absorbing material.

Thus, the larger quantum efficiency of the second photon absorbing material may be, partially or fully, compensated by the smaller distance between the second bottom contact and the common top contact, as compared to the distance between the first bottom contact and the common top contact. Thereby, the absorption for the first and second TFPD may be tuned such that their saturation times are similar. Thus, a high-quality multispectral detector may be enabled. If the first and second TFPD would have the same distance between the bottom contact and the common top contact but very different quantum efficiencies, one TFPD would saturate much faster than the other.

Such a sacrificial layer may protect the photon absorbing material which is deposited first. For example, the photon absorbing material which is deposited first may be protected from intermixing with the photon absorbing material which is deposited later.

The sacrificial layer may be deposited after the deposition of the first photon absorbing material and before the forming of the second opening. Thus, the first photon absorbing material may be protected from etch related damage during etching of the second opening. The first photon absorbing material may also be protected from other damage during forming of the second opening.

The method may further comprise:
planarizing, in an intermediate planarization step, the deposited electrically insulating layer and the deposited first photon absorbing material, wherein the intermediate planarization step is carried out after depositing the first photon absorbing material in the first opening, and before forming the second opening through the electrically insulating layer.

When the second opening is formed after depositing the first photon absorbing material in the first opening it may be advantageous to use an intermediate planarization step such that the patterning resolution for forming the second opening does not degrade due to an uneven surface or a surface that lies above the top surface of the electrically insulating layer.

A tapered opening makes it easier to fully fill the opening and avoid pockets without photon absorbing material in the opening.

In cooperation with attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to a preferable embodiment, being not used to limit the claimed scope. This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

<FIG> illustrates a multipixel detector <NUM> which may be produced according to the method <NUM> of the invention. The illustrated multipixel detector <NUM> has a bottom layer <NUM> comprising a CMOS readout integrated circuit <NUM>, a first bottom electrode <NUM> and a second bottom electrode <NUM>. The first bottom electrode <NUM> and the second bottom electrode <NUM> are arranged on a bottom insulator <NUM> on top of the CMOS readout integrated circuit <NUM> and connected to the CMOS readout integrated circuit <NUM> by via connections <NUM> going through the bottom insulator <NUM>. The first bottom electrode <NUM> and the second bottom electrode <NUM> are embedded in an electrically insulating layer <NUM>. A first <NUM> and second <NUM> opening goes through the electrically insulating layer <NUM> to the first <NUM> and second <NUM> bottom electrode respectively. The first opening <NUM> is at least partially filled with a first photon absorbing material <NUM>. Similarly, the second opening <NUM> is at least partially filled with a second photon absorbing material <NUM>.

The first photon absorbing material <NUM> in the first opening <NUM> is electrically connected to the first bottom electrode <NUM> by a bottom charge carrier control layer <NUM> between the first photon absorbing material <NUM> and the first bottom electrode <NUM>. Similarly, the second photon absorbing material <NUM> in the second opening <NUM> is electrically connected to the second bottom electrode <NUM> by a bottom charge carrier control layer <NUM> between the second photon absorbing material <NUM> and the second bottom electrode <NUM>. Further, both the first <NUM> and second <NUM> photon absorbing materials are electrically connected to a common top electrode <NUM> by a top charge carrier control layer <NUM> which in the illustration is a common top charge carrier control layer <NUM>.

According to the above: the common top electrode <NUM>, the first photon absorbing material <NUM> in the first opening <NUM>, and the first bottom electrode <NUM> form parts of a first TFPD <NUM>. Further, the common top electrode <NUM>, the second photon absorbing material <NUM> in the second opening <NUM> and the second bottom electrode <NUM> form parts of a second TFPD <NUM>.

In the following examples of materials that may be used in the multipixel detector <NUM> will be given.

The first <NUM> and second <NUM> bottom electrodes may comprise metal, e.g. aluminium, copper, tantalum nitride, titanium nitride.

The common top electrode <NUM> may be at least partially transparent. The common top electrode <NUM> may comprise indium tin oxide (ITO), indium gallium zinc oxide (IGZO), or graphene.

Examples of photon absorbing materials that may be used are PbS quantum dots and InAs quantum dots, and/or other quantum dots. The quantum dots may be colloidal quantum dots. Thus, a photon absorbing material may be a colloidal quantum dot thin film. Further examples of photon absorbing materials that may be used are organic semiconductors and/or perovskite material. The first <NUM> and second <NUM> photon absorbing material may be, or comprise, the same material. Alternatively, the first <NUM> and second <NUM> photon absorbing material may be, or comprise, different materials. For example, the first <NUM> and second <NUM> photon absorbing material may be materials with different absorption peak wavelengths. For example, the first photon absorbing material <NUM> may comprise one type of quantum dots and the second photon absorbing material <NUM> may comprise another type of quantum dots, such that the photon absorbing materials have different absorption peak wavelengths. Alternatively, the first <NUM> and second <NUM> photon absorbing material may comprise the same type of quantum dots where the quantum dots of the first photon absorbing material <NUM> have a different size compared to the quantum dots of the second photon absorbing material <NUM>, such that the photon absorbing materials have different absorption peak wavelengths. Further, the first <NUM> and second <NUM> photon absorbing material may be materials of different types. For example, the first photon absorbing material <NUM> may comprise quantum dots and the second photon absorbing material <NUM> may comprise an organic semiconductor material.

A bottom charge carrier control layer <NUM> may comprise at least one of: an electron transport layer, a hole transport layer, an electron blocking layer, a hole blocking layer, an electron injection layer, a hole injection layer.

Similarly, a top charge carrier control layer <NUM> may comprise at least one of: an electron transport layer, a hole transport layer, an electron blocking layer, a hole blocking layer, an electron injection layer, a hole injection layer.

The bottom charge carrier control layer <NUM> and top charge carrier control layer <NUM> may be configured to promote transport of opposite types of charge carriers. In one configuration the bottom charge carrier control layer <NUM> is an electron transport layer and the top charge carrier control layer <NUM> is a hole transport layer. In another configuration the bottom charge carrier control layer <NUM> is a hole transport layer and the top charge carrier control layer <NUM> is an electron transport layer.

Examples of electron transport layer that may be used are TiO<NUM> and Niobium Oxide (NbOx).

Examples of hole transport layer that may be used are nickel oxide (NiOx) and copper oxide (CuOx).

The electrically insulating layer <NUM> may be silicon oxide, silicon nitride, or aluminum oxide.

<FIG> illustrates a flow chart of a method <NUM> for producing a multipixel detector <NUM>, such as the multipixel detector <NUM> of <FIG>. Some steps of the illustrated method are optional, as indicated in the figure. To exemplify the method <NUM>, it will herein be described in conjunction with <FIG> shows a time sequence of illustrations of the multipixel detector <NUM>, seen in cross-section, during production according to the flow chart of <FIG>. In the example given, the optional steps of the <FIG> method <NUM> will be included.

A bottom layer <NUM> comprising a first <NUM> and a second <NUM> bottom electrode is provided S102, as illustrated in <FIG> illustrate how a bottom layer <NUM> may be manufactured. The first <NUM> and a second <NUM> bottom electrode may be arranged on a readout circuit. In <FIG> a CMOS readout integrated circuit <NUM> is used. The CMOS readout integrated circuit <NUM> is shown in <FIG> but excluded from <FIG> for clarity. A bottom insulator <NUM> is arranged on top of the CMOS readout integrated circuit <NUM> and via connections <NUM> going through the bottom insulator <NUM> are formed, <FIG>. A layer of bottom electrode material may then be deposited on the bottom insulator <NUM> (comprising the via connections <NUM>) followed by a bottom charge carrier control layer <NUM>, as seen in <FIG>. Subsequently, the first <NUM> and second <NUM> bottom electrode may be formed out of the layer of bottom electrode material e.g., by patterning and etching said layers. The bottom charge carrier control layer <NUM> may simultaneously be patterned and etched. Thus, in the example method <NUM> the bottom charge carrier control layers <NUM> on the first <NUM> and second <NUM> bottom electrodes are provided S103 before depositing S104 the electrically insulating layer <NUM>, <FIG>. The electrically insulating layer <NUM> is subsequently deposited S104 on the bottom layer <NUM>, as seen in <FIG>. The electrically insulating layer <NUM> may be a silicon oxide, silicon nitride, or aluminum oxide layer. The electrically insulating layer <NUM> may be deposited e.g., through physical vapor deposition or chemical vapor deposition or spin-coating.

The electrically insulating layer <NUM> may then, optionally, be planarized, as seen in <FIG>. Planarizing the electrically insulating layer <NUM> may improve the resolution of coming patterning steps.

A first opening <NUM> through the electrically insulating layer <NUM> to the first bottom electrode <NUM> is then formed S106, as seen in <FIG>. The first opening <NUM> may be formed through patterning, e.g. lithographic patterning and etching.

A first photon absorbing material <NUM> is then deposited S108 in the first opening <NUM> to electrically connect to the first bottom electrode <NUM>, as seen in <FIG>. First photon absorbing material <NUM> may simultaneously be deposited on a top surface of the electrically insulating layer <NUM>. The first photon absorbing material <NUM> may comprise PbS quantum dots and/or InAs quantum dots and/or other quantum dots and/or an organic semiconductor and/or perovskite. The first photon absorbing material <NUM> may be deposited through e.g. spin coating, printing, physical vapor deposition, or evaporation.

<FIG> illustrates an optional intermediate planarization step wherein the deposited electrically insulating layer <NUM> and the deposited first photon absorbing material <NUM> are planarized S110. The intermediate planarization step may form a flat surface comprising a top surface of the electrically insulating layer <NUM> and a top surface of the first photon absorbing material in the first opening <NUM>.

<FIG> illustrates an optional step wherein a sacrificial layer <NUM> is deposited S112. In the illustrated example the sacrificial layer <NUM> is deposited S112 on the surface formed by the intermediate planarization step.

A second opening <NUM> through the electrically insulating layer <NUM> to the second bottom electrode <NUM> is then formed S114, as seen in <FIG>. The second opening <NUM> may be formed through patterning, e.g. lithographic patterning and etching.

A second photon absorbing material <NUM> is then deposited S116 in the second opening <NUM> to electrically connect to the second bottom electrode <NUM>, as seen in <FIG>. Second photon absorbing material <NUM> may simultaneously be deposited on a top surface of sacrificial layer <NUM>, as illustrated. Thus, the sacrificial layer <NUM> may separate the first <NUM> and second <NUM> photon absorbing materials. If a sacrificial layer <NUM> is not used second photon absorbing material <NUM> may simultaneously be deposited on a top surface of the electrically insulating layer <NUM>.

The second photon absorbing material <NUM> may comprise PbS quantum dots and/or InAs quantum dots and/or other quantum dots and/or an organic semiconductor and/or perovskite. The second photon absorbing material <NUM> may be deposited through e.g. spin coating, printing, evaporation or physical vapor deposition.

The deposited electrically insulating layer <NUM>, the deposited first photon absorbing material <NUM> and the deposited second photon absorbing material <NUM> to are then planarized S118 to form a flat surface <NUM>, as seen in <FIG>. Thereby, in the example shown, the sacrificial layer <NUM> is also removed S120. The flat surface <NUM> comprises a top surface <NUM> of the electrically insulating layer <NUM>, a top surface <NUM> of the first photon absorbing material <NUM> in the first opening <NUM> and a top surface <NUM> of the second photon absorbing material <NUM> in the second opening <NUM>, separated from the top surface <NUM> of the first photon absorbing material <NUM> by the top surface <NUM> of the electrically insulating layer <NUM>.

Any of the planarization steps described in the examples above and below may comprise chemical-mechanical polishing and/or grinding and/or fly-cutting.

<FIG> illustrates a top view of a flat surface <NUM>, in this case from what is intended to be a multipixel device comprising a <NUM> by <NUM> TFPDs. Thus, in the flat surface <NUM> there can be seen a row comprising a first <NUM>, second <NUM>, third <NUM>, and fourth <NUM> opening which are respectively filled with a first <NUM>, second <NUM>, third <NUM>, and fourth <NUM> photon absorbing material. In <FIG> there are in total four rows which each may have the same combination of photon absorbing material as the previously described row, as illustrated. The flat surface <NUM> comprises a top surface <NUM> of the electrically insulating layer <NUM>, a top surface <NUM> of the first photon absorbing material <NUM> in the first opening <NUM> and a top surface <NUM> of the second photon absorbing material <NUM> in the second opening <NUM>, separated from the top surface <NUM> of the first photon absorbing material <NUM> by the top surface <NUM> of the electrically insulating layer <NUM>. Further, in the illustration each top surface of photon absorbing material in an opening is separated from the other top surfaces of photon absorbing material by the top surface <NUM> of the electrically insulating layer <NUM>.

Coming back to the example of <FIG> and <FIG>. As seen in <FIG>, the sacrificial layer <NUM> may be removed S120 in the planarization step S118 or in conjunction with the planarization step S118.

Subsequently a common top charge carrier control layer <NUM> may be formed S121. A common top electrode <NUM> is formed S122 electrically connects to the top surfaces <NUM>, <NUM> of the first <NUM> and second <NUM> photon absorbing materials in the flat surface <NUM>. <FIG> may herein be seen as the finished multipixel detector <NUM> after depositing the common top charge carrier control layer <NUM> and the common top electrode <NUM> on the flat surface <NUM> shown in <FIG>.

It should be understood that the steps of the method <NUM> may not necessarily be performed in the order described in conjunction with <FIG>. Further, in some instances some steps may be performed simultaneously. This is exemplified in <FIG> which is a time sequence of illustrations showing a multipixel detector during production, wherein the first <NUM> and second <NUM> photon absorbing materials of the multipixel detector comprises the same material.

<FIG> illustrates a bottom layer <NUM> comprising a first <NUM> and a second <NUM> bottom electrode being provided S102.

<FIG> illustrates an electrically insulating layer <NUM> being deposited S104 on the bottom layer <NUM>.

<FIG> illustrates an optional planarization of the electrically insulating layer <NUM>.

<FIG> illustrates the first <NUM> and second <NUM> opening being formed S106, S114 through the electrically insulating layer <NUM> to the first <NUM> and second <NUM> bottom electrode, wherein the openings are formed simultaneously. For example, the first <NUM> and second <NUM> opening may be defined in the same lithographic patterning step and/or etched simultaneously.

<FIG> illustrates that in this example the first <NUM> and second <NUM> photon absorbing materials are the same material. <FIG> further illustrates the photon absorbing material <NUM>, <NUM> being deposited S108, S116. Thus, in this example the first <NUM> and second <NUM> photon absorbing materials are deposited simultaneously.

<FIG> illustrates the deposited electrically insulating layer <NUM>, the deposited first photon absorbing material <NUM> and the deposited second photon absorbing material <NUM> after being planarized S118 to form a flat surface <NUM>.

<FIG> illustrates a common top charge carrier control layer <NUM> being formed S121.

<FIG> illustrates a common top electrode <NUM> formed S122 on top of the common top charge carrier control layer <NUM>. Thus, the common top electrode <NUM> is also formed S122 on top of the flat surface <NUM>.

In the above examples a bottom charge carrier control layer <NUM> has been provided S103 on the first <NUM> and second <NUM> bottom electrodes before deposition S104 of the electrically insulating layer <NUM>. Alternatively, or additionally, a bottom charge carrier control layer <NUM> may be deposited S107 in the first opening <NUM> before depositing S108 the first photon absorbing material <NUM> in the first opening <NUM> and/or a bottom charge carrier control layer <NUM> may be deposited S107 in the second opening <NUM> before depositing S116 the second photon absorbing material <NUM> in the second opening <NUM>. This will be exemplified below in a method <NUM> according to the flow chart of <FIG>. The method <NUM> will herein be described in conjunction with <FIG> shows a time sequence of illustrations of the multipixel detector <NUM>, seen in cross-section, during production according to the flow chart of <FIG>. In the example given, the optional steps of the <FIG> method <NUM> will be included. In the example, the first <NUM> and second <NUM> photon absorbing materials are the same material. However, the exemplified method <NUM> is applicable also in the case when the first <NUM> and second <NUM> photon absorbing materials are different same materials as well as when the first <NUM> and second <NUM> opening are formed separately.

According to the illustrated method <NUM> a bottom layer <NUM> comprising a first <NUM> and a second <NUM> bottom electrode is provided S102, see <FIG>.

<FIG> illustrate how a bottom layer <NUM> may be manufactured. The first <NUM> and a second <NUM> bottom electrode may be arranged on a readout circuit. In <FIG> a CMOS readout integrated circuit <NUM> is used. The CMOS readout integrated circuit <NUM> is shown in <FIG> but excluded from <FIG> for clarity. A bottom insulator <NUM> is arranged on top of the CMOS readout integrated circuit <NUM> and via connections <NUM> going through the bottom insulator <NUM> are formed, <FIG>. A layer of bottom electrode material may be deposited on the bottom insulator <NUM>, as shown in <FIG>. Subsequently, the first <NUM> and second <NUM> bottom electrode may be formed out of the layer of bottom electrode material e.g. by patterning and etching said layers, see <FIG>, whereby the bottom layer <NUM> is provided S102.

The electrically insulating layer <NUM> is subsequently deposited S104 on the bottom layer <NUM>, as seen in <FIG>.

Further, in this example a bottom charge carrier control layer <NUM> is deposited S107 in the first opening <NUM> and in the in the second opening <NUM>, as seen in <FIG>. In this example, it is one single bottom charge carrier control layer <NUM> which is simultaneously deposited into both openings. The bottom charge carrier control layer <NUM> may conformally coat the surface, it may be deposited by a conformal coating technique. Thus, the first <NUM> and second <NUM> bottom electrode as well as the side walls of the first <NUM> and second <NUM> openings may be covered by said bottom charge carrier control layer <NUM>, as illustrated. The surface may then optionally be planarized, as seen in <FIG>.

<FIG> illustrates that in this example the first <NUM> and second <NUM> photon absorbing materials are the same material. <FIG> further illustrates the structure after deposition S108, S116 of the photon absorbing material <NUM>, <NUM>, in this example being the same material, and planarization S118 to form a flat surface <NUM>. After planarization S118 a part <NUM> of the bottom charge carrier control layer <NUM> may lie within the flat surface <NUM>. If a common top charge carrier control layer <NUM> and/or a common top electrode <NUM> would be formed on top of said part <NUM> of the bottom charge carrier control layer <NUM> a defective pixel could be formed. This may e.g. be avoided by the formation of an electrically insulating barrier <NUM>.

In this example an electrically insulating barrier <NUM> is formed S124 on the flat surface <NUM>, as seen in <FIG>. An electrically insulating barrier material may be deposited as a layer and patterned and etched to form opening to the first <NUM> and second <NUM> photon absorbing materials, as also seen in <FIG>. The patterning may be such that the part <NUM> of a bottom charge carrier control layer <NUM> lying within the flat surface <NUM> is covered.

<FIG> illustrates a multipixel detector wherein the first bottom electrode <NUM> is arranged at a first distance from the common top electrode <NUM> and the second bottom electrode <NUM> is arranged at a second distance from the common top electrode <NUM>, wherein the second distance is smaller than the first distance. Herein the quantum efficiency of the second photon absorbing material <NUM> may be larger than the quantum efficiency of the first photon absorbing material <NUM>. First <NUM> and second <NUM> bottom electrodes with different height may be implemented in any of the above given examples. <FIG> further illustrates the first <NUM> and second <NUM> opening being tapered. Tapered openings may be implemented in any of the above given examples.

It should be understood that the method <NUM> may comprise further steps than the ones described above. For example, after forming the common top electrode <NUM>, the multipixel detector may be further processed to form a focal plane array.

Claim 1:
A method (<NUM>) for producing a multipixel detector (<NUM>), the method (<NUM>) comprising:
providing (S102) a bottom layer (<NUM>) comprising a first (<NUM>) and a second (<NUM>) bottom electrode;
depositing (S104) an electrically insulating layer (<NUM>) on the bottom layer (<NUM>);
forming (S106) a first opening (<NUM>) through the electrically insulating layer (<NUM>) to the first bottom electrode (<NUM>);
depositing (S108) a first photon absorbing material (<NUM>) in the first opening (<NUM>) to electrically connect to the first bottom electrode (<NUM>);
forming (S114) a second opening (<NUM>) through the electrically insulating layer (<NUM>) to the second bottom electrode (<NUM>);
depositing (S116) a second photon absorbing material (<NUM>) in the second opening (<NUM>) to electrically connect to the second bottom electrode (<NUM>);
planarizing (S118) the deposited electrically insulating layer (<NUM>), the deposited first photon absorbing material (<NUM>) and the deposited second photon absorbing material (<NUM>) to form a flat surface (<NUM>), wherein the flat surface (<NUM>) comprises a top surface (<NUM>) of the electrically insulating layer (<NUM>), a top surface (<NUM>) of the first photon absorbing material (<NUM>) in the first opening (<NUM>) and a top surface (<NUM>) of the second photon absorbing material (<NUM>) in the second opening (<NUM>), separated from the top surface (<NUM>) of the first photon absorbing material (<NUM>) by the top surface (<NUM>) of the electrically insulating layer (<NUM>);
forming (S122) a common top electrode (<NUM>) on top of the flat surface (<NUM>), wherein the common top electrode (<NUM>) electrically connects to the top surfaces (<NUM>, <NUM>) of the first (<NUM>) and second (<NUM>) photon absorbing materials in the flat surface (<NUM>);
wherein the common top electrode (<NUM>), the first photon absorbing material (<NUM>) in the first opening (<NUM>) and the first bottom electrode (<NUM>) form parts of a first thin film photodiode, first TFPD, (<NUM>); and the common top electrode (<NUM>), the second photon absorbing material (<NUM>) in the second opening (<NUM>) and the second bottom electrode (<NUM>) form parts of a second thin film photodiode, second TFPD, (<NUM>).