Patent ID: 12199209

EXEMPLARY EMBODIMENTS

FIGS.1A and1Beach illustrate, in a highly schematic fashion, an exemplary embodiment of an optical sensor110according to the present invention in a side view. Accordingly, the optical sensor110comprises a layer112of at least one photoconductive material114. In particular, the layer112of the photoconductive material114may exhibit a thickness of 10 nm to 100 μm, preferably of 100 nm to 10 μm, more preferred of 300 nm to 5 μm. In a preferred embodiment, the layer112of the photoconductive material114may comprise an essentially flat surface, wherein, however, other embodiments which may exhibit variations of the surface of the layer112, such as gradients or steps, may also be feasible. Herein, the layer112of the photoconductive material114may, preferably, be manufactured as described below with respect toFIG.3. However, other manufacturing methods may also be feasible.

In the exemplary embodiments ofFIG.1, the photoconductive material114may be or comprise at least one chalcogenide which can, preferably, be selected from a group comprising sulfide chalcogenides, selenide chalcogenides, telluride chalcogenides, and ternary chalcogenides. In particular, the photoconductive material114may be or comprise a sulfide, preferably lead sulfide (PbS), a selenide, preferably lead selenide (PbSe), or a ternary chalcogenide, preferably lead sulfoselenide (PbSSe). Since many of the preferred photoconductive materials114are, generally, known to exhibit a distinctive absorption characteristic within the infrared spectral range, the optical sensor110may, preferably, be used as an infrared sensor. However, other embodiments and/or other photoconductive materials, in particular, the photoconductive materials as described elsewhere in this document for the present purpose, may also be feasible.

Further, the optical sensor110according to the present invention comprises a cover116, wherein the cover116, preferably fully, covers an accessible surface118of the photoconductive material114. As already described above, the cover116may, thus, be adapted for providing an encapsulation for the photoconductive material114, in particular, as an hermetic package, in order to avoid a degradation of the optical sensor110or a partition thereof, in particular of the photoconductive material114, by external influence, such as humidity and/or oxygen. As mentioned above, the cover116is an amorphous cover comprising at least one metal-containing compound120. In a particularly preferred embodiment as described here, the metal-containing compound120may comprise a metal selected from the group consisting of Al, Zr, Hf, Ti, Ta, Mn, Mo, and W, wherein the metals Al, Ti, Zr, and Hf are especially preferred. However, other kinds of metals, in particular the metals as indicated elsewhere for this purpose in this document, may also be feasible. Further, the metal-containing compound120may be selected from a group comprising an oxide, a hydroxide, a chalcogenide, a pnictide, a carbide, or a combination thereof.

In this particular embodiment, the metal-containing compound120may, preferably, comprise at least one oxide of Al, at least one hydroxide of Al, or a combination thereof, which may also be expressed by the formula AlOx(OH)ywith 0≤x≤1.5 and 0≤y≤1.5, wherein x+y=1.5. In this particular embodiment, the cover116may exhibit a thickness of 10 nm to 600 nm, preferably of 20 nm to 200 nm, more preferred of 40 nm to 120 nm, most preferred of 50 to 95 nm. This range of thickness may, in particular, reflect the amount of metal-containing compounds120within the cover116that may be advantageous to achieve the above-mentioned functions of providing encapsulation for the photoconductive material114.

Further in this particular embodiment, the cover116may be a conformal cover with respect to the adjacent surface118of the photoconductive material114. As defined above, the thickness of the conformal cover may, thus, follow the corresponding surface118of the photoconductive material114within a deviation of ±50 nm, preferably of ±20 nm, mostly preferred of ±10 nm, wherein the deviation may occur for at least 90%, preferably for at least 95%, mostly preferred for at least 99%, of a surface122of the cover116, hereby leaving aside any contamination or imperfection that may be present on the surface122of the cover116.

Alternatively, the metal-containing compound120may comprise at least one oxide of Zr, at least one hydroxide of Zr, or a combination thereof, which may also be expressed by the formula ZrOx(OH)ywith 0≤x≤2 and 0≤y≤2, wherein x+y=2. However, other kinds of metal-containing compounds120, in particular of Hf, may also be feasible. In all cases, rests of unreacted organic ligands could, additionally, be present.

As further illustrated in each ofFIGS.1A and1B, the at least one layer of the photoconductive material114is, preferably directly, applied to at least one substrate124, wherein the substrate124may, preferentially, be or comprise an insulating substrate. Herein, the thickness of the substrate124may be of 10 μm to 2000 μm, preferably of 50 μm to 1000 μm, more preferred of 100 μm to 500 μm. In order to allow an incident light beam126to reach the photoconductive material114in order to optically modify an electrical conductivity within the layer112of the photoconductive material114, at least one of the cover116and the substrate124is optically transparent within a desired wavelength range, such as in the infrared spectral range or a partition thereof.

As schematically depicted inFIG.1A, a beam path128of an incident light beam126may be configured to pass through the cover116in order to generate a light spot having a diameter130within the layer112of the photoconductive material114. As a result, it may, particularly, be advantageous to select the metal-containing compound120for the cover116to be, preferably, optically transparent within the desired wavelength range, in particular, by exhibiting a suitable absorption characteristic. Alternatively (not depicted here), it may, however, be preferred to select the metal-containing compound120for the cover116not to be optically transparent within the desired wavelength range. Such a kind of selection may, in particular, be advantageous in a case in which a specific metal-containing compound120may exhibit particularly preferred properties for the optical sensor110apart from offering optical transparency within the desired wavelength range. In addition, it may be preferred that one or both the metal-containing compound120used for the cover116and the material applied for the substrate124may exhibit optically transparent properties within the desired wavelength range, such as for allowing a sensing of the light beam126from both directions of the optical sensor110. Herein, the substrate124may comprise an optically transparent material132, in particular a glass. However, other materials that may be at least partially optically transparent in the infrared spectral range may also be feasible.

In contrast to optical sensors which are known from prior art, especially from WO 2018/019921 A1, the cover116not only covers the accessible surface118of the photoconductive material114apart from an area at which the cover116meets the substrate124where the preferably conformal cover116necessarily touches the substrate124at a negligible part of its surface but also an accessible surface134of the substrate124. Preferably, the cover116may be applied in a manner that it may fully contact all accessible surfaces118,134of the photoconductive material114and of the substrate124, respectively. In particular, the cover116may be applied in a manner that it may directly contact a top and sides of the layer112of the photoconductive material114and at least the sides of the substrate124. However, other kinds for providing an encapsulation for the photoconductive material114, in particular, as hermetic package may also be feasible. As a result, the cover116may, thus, prevent a direct contact between the layer112of the photoconductive material114or of the substrate124with a surrounding atmosphere, thereby avoiding a degradation of the photoconductive material114by external influence, such as humidity and/or oxygen.

Compared to the cover layer as disclosed in WO 2018/019921 A1 which is only deposited on the layer of the photoconductive material, the cover116according to the present invention significantly improves the long-term stability of the optical sensor110. As can be derived from a comparison of the following Tables 1 and 2, this effect can be experimentally verified. For this purpose, values of a dark resistance in MO were measured and showed a difference with increasing duration of exposure of various samples of the optical sensor110to an ambient atmosphere (standard pressure) at 26° C. The dark resistance was measured by using a voltage divider circuit having 10 V/mm and linearly extrapolated to 50 V/mm. Herein, the layer112of the photoconductive material114in each of the samples comprised a chip of PbS having a 2×2 mm2active area.

As presented in Table 1, samples A1 to A7 comprised a cover layer according to the state of the art, in particular as disclosed in WO 2018/019921 A1:

TABLE 1(state of the art)sampledark resistance/MΩtime/hours0105010050010001500A10.30.30.30.30.30.30.2A20.30.30.30.30.30.20.2A30.30.30.30.30.30.20.2A40.30.30.30.30.30.30.3A50.30.30.30.30.30.20.2A60.30.30.30.30.30.20.1A70.30.30.30.30.30.30.2

In contrast hereto, samples B1 to B7 as presented in Table 2 comprised a cover116according to the present invention:

TABLE 2(present invention)sampledark resistance/MΩtime/hours0105010050010001500B10.30.30.30.30.30.30.3B20.30.30.30.30.30.30.3B30.30.30.30.30.30.30.3B40.30.30.30.30.30.30.3B50.30.30.30.30.30.30.3B60.30.30.30.30.30.30.3B70.30.30.30.30.30.30.3

While samples A1 to A7 which were prepared according to the state of the art started to show a decreased value for the dark current after 1000 to 1500 hours of exposure, samples B1 to B7 which were prepared according to the present invention did not show any decrease of the dark current within the same duration of exposure. As a result, the cover116according to the present invention improves a reduction or exclusion of external influences by additionally minimizing or diminishing an effect of humidity and/or oxygen onto the layer112of the photoconductive material114, especially by blocking and/or obstructing paths that may be capable of transferring humidity and/or oxygen through or along the surface of the substrate124to the layer112of the photoconductive material114.

As further illustrated inFIGS.1A and1B, the optical sensor110according to the present invention comprises at least two individual electrical contacts136,136′, i.e. at least one first electrical contact136and at least one second electrical contact136′, wherein the electrical contacts136,136′ are adapted to contact the layer112of the photoconductive material114. For this purpose, the electrical contacts136,136′ may be configured and arranged in a manner in order to be able to guide an electrical current via the first electrical contact136through the layer112of the photoconductive material114to the second electrical contact136′ or vice-versa, or to apply a voltage across the layer112of the photoconductive material114by using the first electrical contact136and the second electrical contact136′. For both purposes, the first electrical contact136may be electrically isolated from the second electrical contact136′ while both the first electrical contact136and the second electrical contact136′ are in direct connection with the layer112of the photoconductive material114. As further illustrated herein, the cover116may at least partially coat the electrical contacts136,136′, which may, especially, be configured to be bondable, such as to one or more leads138,138′ that may lead to an external circuit as depicted inFIG.1B.

The direct connection between any one of the electrical contacts136,136′ and the layer112of the photoconductive material114may be provided by any known process capable of providing electrical contacts, such as plating, welding, soldering, wire bonding, thermosonic bonding, stitch-bonding, ball-bonding, wedge bonding, compliant bonding, thermocompression bonding, anodic bonding, direct bonding, plasma-activated bonding, eutectic bonding, glass frit bonding, adhesive bonding, transient liquid phase diffusion bonding, surface activated bonding, tape-automated bonding, or depositing electrically highly conductive substances at the contact zones. In order to allow a sufficient electrical conductivity through the electrical contacts136,136′ while, concurrently, providing an sufficient mechanical stability of the electrical contacts136,136′, the electrical contacts136,136′ may, preferably, comprise at least one electrode material selected from the group consisting of the metals Ag, Cu, Pt, Al, Mo or Au, an alloy comprising at least one of the mentioned metals, as well as graphene. However, other kinds of electrode materials may also be feasible.

As schematically depicted inFIG.1B, the substrate124may be attached, preferably via a thin film140of glue, to a circuit carrier device142, in particular to a printed circuit board (PCB)144. For this purpose, wires, such as gold wires, beryllium-doped gold wires, aluminum wires, platinum wires, palladium wires, silver wires, or copper wires, may be used as the leads138,138′ for bonding the electrical contacts136,136′, such as contact pads (not depicted here) on the circuit carrier device142. In the particularly preferred embodiment as illustrated inFIG.1B, the electrical contacts136,136′ may be bondable through the cover116. This feature may, in particular, allow improving the encapsulation function of the cover116and, concurrently, providing stability to the electrical contacts136,136′.

FIG.2illustrates, in a highly schematic fashion, an exemplary embodiment of an optical detector150according to the present invention which may, preferably, be adapted for use as an infrared detector. However, other embodiments are feasible. The optical detector150comprises at least one of the optical sensors100as described above in more detail, which may be arranged along an optical axis of the detector150. Specifically, the optical axis may be an axis of symmetry and/or rotation of the setup of the optical sensor100. The optical sensor100may be located inside a housing of the detector150. Further, at least one transfer device may be comprised, preferably a refractive lens. An opening in the housing, which may, particularly, be located concentrically with regard to the optical axis may, preferably, define a direction of view of the detector150.

Further, the optical sensor100is designed to generate at least one sensor signal in a manner dependent on an illumination of a sensor region152by the light beam126. Herein, the detector150may have a straight beam path or a tilted beam path, an angulated beam path, a branched beam path, a deflected or split beam path or other types of beam paths. Further, the light beam126may propagate along each beam path or partial beam path once or repeatedly, unidirectionally or bidirectionally.

According to the FiP effect, the optical sensor100may provide a sensor signal which, given the same total power of the illumination, is dependent on a beam cross-section130of the light beam126within the sensor region. However, other kinds of signals may also be feasible. As indicated above, the sensor region152comprises at least one of the layers112of the photoconductive material114, preferably, a chalcogenide, in particular lead sulfide (PbS), lead selenide (PbSe), or lead sulfoselenide (PbSSe). However, other photoconductive materials114, in particular other chalcogenides, may be used. As a result of the use of the photoconductive material114in the sensor region152, an electrical conductivity of the sensor region152, given the same total power of the illumination, depends on the beam cross-section of the light beam126in the sensor region152. Consequently, the resulting sensor signal as provided by the optical sensor110upon impingement by the light beam126may depend on the electrical conductivity of the photoconductive material114in the sensor region152and, thus, allows determining the beam cross-section130of the light beam126in the sensor region152.

Via further electrical leads154,154′ to which the leads138,138′ are bonded, the sensor signal may be transmitted to an evaluation device156, which is, generally, designed to generate at least one item of information by evaluating the sensor signal of the optical sensor110. For this purpose, the evaluation device156may comprise one or more electronic devices and/or one or more software components, in order to evaluate the sensor signals. Generally, the evaluation device156may be part of a data processing device158and/or may comprise one or more data processing devices158. The evaluation device156may be fully or partially integrated into the housing and/or may fully or partially be embodied as a separate device which is electrically connected in a wireless or wire-bound fashion to the optical sensor100. The evaluation device156may further comprise one or more additional components, such as one or more electronic hardware components and/or one or more software components, such as one or more measurement units and/or one or more evaluation units and/or one or more controlling units (not depicted here).

FIGS.3A to3Cillustrates, in a highly schematic fashion, an exemplary embodiment of a method for manufacturing the optical sensor110according to the present invention.

As illustrated inFIG.3A, prior to providing the layer112of the photoconductive material114, the electrical contacts136,136′ may be generated, such as in form of an evaporated metal layer which can be provided by known evaporation techniques on the substrate124, preferably, comprising glass as the optically transparent material132. In particular, the evaporated metal layer may comprise one or more of Ag, Al, Pt, Mg, Cr, Ti, or Au. Alternatively, the electrical contacts136,136′ may comprise a layer of graphene. However, as mentioned above in more detail, other methods of generating the electrical contacts136,136′ may also be feasible.

As further illustrated inFIG.3A, the layer112of the photoconductive material114is, subsequently, provided. For this purpose, the photoconductive material114may be synthesized according to the following procedure. Accordingly, 0.015 mol/L thiourea or substituted products thereof, 0.015 mol/L lead acetate, lead nitrate, or substituted products thereof, and 0.15 mol/L sodium hydroxide or substituted products thereof are dissolved in a reaction volume, whereby a clear solution is obtained at room temperature. As known from prior art, when the solutions mentioned above are intermixed in any order, lead sulfide (PbS) precipitates out of the solution at a temperature above 30° C., usually, in such a manner that an even and relatively smooth layer may be formed on side walls and at a bottom of a liquid-containing reactor or on the walls of any object located within therein.

However, when immediately prior to the actual precipitation of PbS from the intermixed precipitating solution, an aqueous solution of an agent capable of liberating relatively abundant quantities of nascent oxygen, preferably, of potassium persulfate, hydrogen peroxide, or sodium perborate, is added thereto, PbS precipitates therefrom in the usual manner but in an activated form being capable of direct use within a cell or of additional sensitization by aging or low-temperature baking. The precipitating solution and the activating agent are preferably mixed at a temperature above 35° C. and stirred for one to three hours, during which time deposition occurs. Herein, an amount of the persulfate ion, perborate ion, or nascent oxygen from the hydrogen peroxide, expressed in moles, added to the liquid solution for precipitating PbS may, preferably, be 0.01 to 0.5 of the theoretical amount of PbS in the bath, expressed in moles, wherein the theoretical amount of PbS is that amount which would be formed if there were a total conversion of the lead and sulfur precipitating compounds to lead sulfide.

After formation of the PbS layer, an ageing step in a climate chamber, preferably at a temperature of approx. 50° C. and a humidity above 70%, may optionally be performed, which appears to be beneficial for the photoconductive performance. Improved photoconductivity may be obtained when deposited and aged films are further processed by annealing, i.e. by heating in vacuum or air at a temperature of approx. 100° C. to 150° C. for 1 to 100 hours.

However, other kinds of providing the layer112of the photoconductive material114may also be feasible.

FIG.3Bschematically illustrates depositing the metal-containing compound120as an amorphous cover116on the accessible surfaces118,134of the layer112of the photoconductive material PbS114and of the substrate124, in order to function, in particular, as an encapsulation layer. For this purpose, at least one precursor which is adapted to react to the metal-containing compound120can be applied. In this preferred embodiment, an atomic layer deposition (ALD) process or the combination of ALD and sputtering has been used as the deposition method. Alternatively, other deposition processes, such as a chemical vapor deposition (CVD) process, may, however, also be applied.

In a preferred embodiment of the present invention, the cover116comprises Al2O3which has been generated via the ALD process or the combination of an ALD process and a sputtering process. Alternatively, laminates like Al2O3/TiO2/Al2O3/ . . . or Al2O3/ZrO2/Al2O3/ . . . may also be produced. In this particular embodiment, the ALD process has been performed applying the following process parameters:first precursor: H2O;second precursor: Al(CH3)3(trimethylaluminum, TMA);temperature approx. 60° C.;approx. 700 cycles.

As further depicted inFIG.3B, the Al2O3-comprising cover116may be applied in accordance with the present invention in a fashion that it may be, concurrently, coat the accessible surface118of the photoconductive PbS layer112, the electrical contacts136,136′ which may contact the photoconductive PbS layer112, and the accessible surface134of the substrate124.

As illustrated inFIG.3C, the two electrical contacts136,136′ which electrically contact the layer112of the photoconductive material114may, preferably finally, be bonded to at least one external connection by electrically conductive leads138,138′, such as gold wires, which may be provided here through the cover116. However, as mentioned above, other ways for providing electrical contacts136,136′ to the photoconductive PbS layer112may also be feasible, such as by providing the leads138,138′ already prior to depositing the amorphous cover116, i.e. in an intermediate process step between the process steps as illustrated inFIGS.3A and3B.

In a particularly preferred embodiment, the layer112of the photoconductive material114may comprise at least two individual sensor areas (not depicted here), preferably an array of individual sensor areas, which are directly or indirectly applied to the same substrate124, which may also be denoted as a “common substrate”, which may, thus, exhibit a considerably large area. In this particular embodiment, the individual sensor areas are, firstly directly or indirectly applied to the common substrate124, wherein at least two individual electrical contacts136,136′ are provided for contacting each of the individual sensor areas within the112layer of the photoconductive material114. Thereafter, the individual sensor areas are separated from each other in a fashion that each of the individual sensor areas is carried by a respective portion of the substrate124. Finally, the cover116is deposited on the accessible surfaces118,134of each of the individual sensor areas and of the respective portion of the substrate124.

LIST OF REFERENCE NUMBERS

110sensor112layer of photoconductive material114photoconductive material116cover118accessible surface of the layer of the photoconductive material120metal-containing compound122surface of the cover124substrate126light beam128beam path130diameter of light beam; beam cross-section132optically transparent material134accessible surface of the substrate136,136′ electrical contacts138,138′ electrically connecting leads140thin film of glue142circuit carrier device144printed circuit board150optical detector152sensor region154,154′ further electrical leads156evaluation device158processing device