Liquid-oriented manufacturing process for a conversion crystal

Abstract

A liquid-oriented manufacturing process for a conversion crystal (30) comprising the steps: a) supplying a germination crystal (20); b) forming a growth mask (12) on the germination crystal (20); c) positioning the germination crystal (20) so that it is oriented with a first crystal plane (20d) parallel to a support face (11a) of a substrate (11) and with at least one growth face (20a) of the germination crystal (20) arranged transversely to the support face of the substrate (11); d) applying the liquid precursor (40) of the conversion crystal (30) configured in a state of relative supersaturation at least at the level of the flat, smooth portion of the growth face (20a) to obtain free growth of the conversion crystal (30). Figure 2

Description

Title of the invention: Liquid-oriented manufacturing process for a conversion crystal technical field

[0001] The invention relates to a method for manufacturing a conversion crystal by liquid process. STATE OF PRIOR ART

[0002] In the field of ionizing radiation detectors (X-rays, gamma rays, charged or uncharged particles such as alpha and beta particles, protons, neutrons, etc.), it is important to detect the amount of radiation received as precisely as possible, ideally at an acceptable cost. It is therefore very advantageous to obtain a conversion crystal layer with a significant thickness, i.e., greater than 1 micrometer, or even greater than 100 micrometers, in order to efficiently absorb the incident radiation. This makes it possible to measure a large quantity of radiation without it passing through the conversion crystal. This radiation is directly converted into electrical charges. This is called a direct conversion detector.For measurement quality and reliability, it is also important that the conversion crystal layer have a crystallinity close to that of a single crystal and a high density to limit the ability of radiation to pass through the conversion crystal layer. For many applications, such as radiography, the surface area of ​​the layer must be several tens or even several hundreds of square centimeters.

[0003] In this context, it is known to carry out liquid deposition, for example by spin-die centrifugation or by methods known under the Anglo-Saxon terminology "slot-die" or "doctor blade". These methods are suitable for obtaining thin films with a thickness of less than 1 micrometer, but they do not allow the production of films with thicknesses exceeding several tens of micrometers while maintaining a crystalline structure as close as possible to that of a single crystal.

[0004] Several techniques for coupling on a surface of thick layers of perovskites, by liquid means, have already been proposed.

[0005] Thus, the document "Kovalenko, Nat. Phot. 9 (2015) 444" describes a spray-coating process for depositing a thick layer (10-100 micrometers) of CH3NH3 Pbl3 (MAPI) onto a surface with a metallic electrode to create a detector device. This process is difficult to control for layers thicker than 100 micrometers. Moreover, the resulting layers have a poorly controlled and very Polycrystalline, with many grain boundaries, which is not favorable for optoelectronic properties. The thickness and surface finish are also difficult to control.

[0006] The document "Nature 550 (2017) 87" proposes a technique for depositing thick layers using a liquid method. They use an ink of MAPI microparticles suspended in a solvent. These microparticles are then deposited onto the surface (for example, onto a transistor active array) by coating. After removal of the solvent, the layer consists of an agglomerate of microparticles (with typical dimensions on the order of 30 micrometers) that percolate with one another. The layer thus produced is porous. In the case of photodetectors, this morphology is not favorable for the extraction of photogenerated charge carriers, which must percolate from one microcrystal to another. Moreover, due to the porosity, the layer is less dense, which is not favorable for the absorption of energetic radiation (X-rays, gamma rays).

[0007] Document WO 2017 / 046390 Al proposes depositing a first perovskite layer (nucleation layer) on the substrate surface, then growing a second, thicker perovskite layer in solution from the first layer. The described technique requires using a nucleation layer different from the layer to be grown, which can pose problems in the case of a detector device by blocking charge carrier collection. The layer thus produced is highly polycrystalline (many grain boundaries). Grain boundaries are discontinuous and disturbed regions that can lead to a decrease in performance (areas with a higher density of electron traps, areas more favorable to ion migration).Furthermore, the final thickness is highly likely to be very inhomogeneous due to the natural misorientation of the crystallographic axes of the nucleation layer, and due to the different possible growth kinetics depending on the inhomogeneities of the nucleation layer. Finally, the conditions for resuming growth on the thin nucleation layer without dissolving it will be very delicate.

[0008] The document "Huang J., Nat. Phot. 11 (2017) 315" proposes growing a single crystal of MAPbBr3, measuring approximately 1 cm in lateral dimensions, on a surface by initiating nucleation from a seed placed on the surface. In this configuration, the crystal cannot grow laterally to the surface without also growing in the direction normal to the surface, implying an increase in thickness. It is difficult to envision extending this technique to larger surfaces (greater than a few square centimeters). In the case where several seeds were initially placed on the surface, the parallel growth of these different seeds would pose problems in terms of thickness homogeneity and disorientation of these seeds, but also grain boundaries and strong associated stresses between crystals.

[0009] Finally, the document "Adv. Mater. 2017, 1602639" describes a technique for coupling a thick layer (between 100 and 800 micrometers) of MAPbBr3 by confining the growth between two plates describing two opposing surfaces. In this document, an overlap area of ​​120 square centimeters is demonstrated. However, this technique is difficult to implement because it requires continuously renewing the growth solution between the two closely spaced plates to continuously feed the crystal growth. The final layer exhibits significant inhomogeneities in thickness and the number of grain boundaries. These two parameters are critical because they directly impact the conversion performance. Description of the invention

[0010] The present invention aims to address all or part of the problems presented above.

[0011] In particular, one aim is to provide a solution that meets at least one of the following objectives:

[0012] - obtain a thick layer, of satisfactory quality, of conversion crystal di directly in an optoelectronic device;

[0013] - obtain a conversion crystal of satisfactory crystallinity and having a thickness controlled.

[0014] This goal can be achieved through the implementation of a liquid-oriented manufacturing process for a conversion crystal, the process comprising the following steps a) provide a germination crystal enabling the growth of the conversion crystal to be manufactured; b) form a growth mask on the germination crystal, the growth mask being configured to prevent the growth of the conversion crystal to be manufactured at the location where the growth mask is formed on the germination crystal, the growth mask being formed so as to cover on the one hand an upper edge of the germination crystal arranged distally to a support face of a substrate on which the germination crystal is positioned in step c), on the other hand a part of the germination crystal except for at least one growth opening delimited in the growth mask; c) Position the germination crystal on the substrate support face so that the germination crystal is oriented so that a first crystal plane, corresponding to a stable growth orientation face of the germination crystal, is parallel to the support face and so that at least one growth face of the germination crystal is arranged transversely to the substrate support face, the growth aperture being arranged at the growth face so that only a flat and smooth portion of the growth face is suitable for contact with a liquid precursor of the conversion crystal; d) apply the liquid precursor of the conversion crystal configured in a state of relative supersaturation at least at the level of the flat and smooth portion of the growth face to obtain free growth of the conversion crystal, from the flat and smooth portion of the growth face, according to a growth thickness contained between the support face of the substrate and a top edge of the growth opening arranged distally to the support face of the substrate.

[0015] Some preferred but not limiting aspects of this manufacturing process are the following, taken individually or in combination.

[0016] In one implementation of the manufacturing process, the process includes the following additional step: dO) configure the liquid precursor of the conversion crystal so that it is in a state of undersaturation at least at the level of the flat and smooth portion of the growth face, step dO) being carried out before step d).

[0017] In one implementation of the manufacturing process, during step d), the growing conversion crystal includes a flat upper facet, parallel to the support face, and whose dislocations are inactive.

[0018] In one implementation of the manufacturing process, during step c), the orientation of the germination crystal is achieved to within at least 0.1°.

[0019] In one implementation of the manufacturing process, during step b), the growth mask is formed so as to cover a lower edge of the germination crystal arranged proximally with respect to the support face of the substrate.

[0020] In one implementation of the manufacturing process, the upper edge of the growth opening is parallel to the support face of the substrate.

[0021] In one implementation of the manufacturing process, during step b), at least one additional growth opening is arranged on at least one additional growth face of the germination crystal arranged transversely to the support face of the substrate.

[0022] In one implementation of the manufacturing process, the germination crystal and the conversion crystal to be manufactured have a cubic atomic structure.

[0023] In one implementation of the manufacturing process, the conversion crystal to be manufactured is a perovskite of type ABX3, A'2C1+D3+X6, A2B4+X6 or A3B23+X9 with A, A', C, D and B being cations and X an anion; A, B, C, D, X being a single element or a mixture of at least two elements.

[0024] In one implementation of the manufacturing process, the conversion crystal to be manufactured is an organic-inorganic hybrid perovskite of formula A(1)i-(y2+...+yn)A(2) y2... A(n'ynB(1'1_(Z2+...+zm)B(2'z2.. .6(^^)3^2+,,,+^^ • .X(p'xp, respecting the electronic neutrality rule, with A(n) and B(n) cations, X(n) an anion and n, m, p integers.

[0025] In one implementation of the manufacturing process, the growth face has a crystallographic orientation of a plane {1,0,0} or a plane {1,1,0}.

[0026] In one implementation of the manufacturing process, during step b), the growth mask is formed by an adhesive.

[0027] In one implementation of the manufacturing process, the process includes the following step, implemented after step d): e) treat the conversion crystal so as to make at least one of the faces of the conversion crystal straight.

[0028] In one implementation of the manufacturing process, the germination crystal is composed of several germs assembled together.

[0029] In one implementation of the manufacturing process, during step d), the temperature of the liquid precursor of the conversion crystal is changed gradually over time.

[0030] In one implementation of the manufacturing process, during step c), the positioning of the germination crystal is carried out so that the germination crystal is offset from an area of ​​the substrate where the conversion crystal to be manufactured is formed.

[0031] In one implementation of the manufacturing process, the process includes the following step implemented after step d): f) treat the conversion crystal so as to make the germination crystal and the conversion crystal independent of each other.

[0032] The invention also relates to an optoelectronic device comprising a conversion crystal obtained by growth in the optoelectronic device and according to such a process, wherein the conversion crystal has a thickness greater than or equal to 100 micrometers. Brief description of the drawings

[0033] Other aspects, objectives, advantages and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0034] [fig. 1] Fig. 1 illustrates in schematic cross-sectional view the steps of an example of a process according to the invention where a germination crystal is positioned on a substrate and is partially covered by a growth mask, which does not cover the lower edge of the germination crystal.

[0035] [fig-2] Fig. 2 illustrates in schematic cross-sectional view, before and during growth of the conversion crystal, steps of an example of a process according to the invention where a germination crystal is positioned on a substrate and is partially covered by a growth mask which covers the lower edge of the germination crystal.

[0036] [fig.3] Fig.3 illustrates, in a schematic top view, the steps of an example of process according to the invention wherein the germination crystal is first offset from an area of ​​the substrate where the conversion crystal to be manufactured is to be formed then, during the growth of the conversion crystal, the conversion crystal covers this area and the germination crystal is made independent of the conversion crystal obtained by growth.

[0037] [fig.4] Fig.4 illustrates a cross-sectional view of a nucleation crystal whose mask growth is achieved with glue.

[0038] [fig.5] Fig.5 illustrates a temperature profile applied to the liquid precursor of conversion crystal during the growth of the conversion crystal.

[0039] [fig.6] Fig.6 illustrates an example of a method according to the invention where, during the step b) an additional growth opening is arranged on a face of the germination crystal opposite to the growth face.

[0040] [fig.7] Fig.7 illustrates an example of a manufacturing device implementing a example of a manufacturing process according to the invention.

[0041] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0042] In Figures 1 to 7 attached and throughout the description, identical or similar functional elements are identified by the same reference numerals. Furthermore, the various elements are not drawn to scale in order to prioritize the clarity of the figures and facilitate their understanding.

[0043] Moreover, the different modes or examples and variants are not mutually exclusive and can, on the contrary, be combined with each other.

[0044] The invention relates essentially to a method for manufacturing a conversion crystal 30 by liquid means, which will be described in detail below.

[0045] The application areas targeted by this manufacturing process include, in particular, processes for obtaining X-ray or gamma-ray detectors for medical radiography, processes for manufacturing non-destructive testing sensors, sensors dedicated to safety functions, processes for manufacturing sensors dedicated to the nuclear field, and processes for manufacturing detectors or sensors for detection in large scientific instruments for astronomy and particle physics. However, it is emphasized that these areas are not exhaustive. For example, obtaining photoelectric crystals used in the construction of scintillators adapted to converting X-ray or gamma photons into visible photons can be considered. The same applies to the manufacture of detectors operating in other wavelengths of electromagnetic radiation. such as visible photons with wavelengths between 400 and 800 nm or near-infrared photons with wavelengths greater than 800 nm. Finally, the invention can find application in X-ray imaging for all radiography modalities, regardless of format, for example fluoroscopy, mammography, dental imaging or CT scans.

[0046] In particular, the invention can be used in modalities where it is important to have a strong signal for a minimum dose administered to the patient, such as in cardiac imaging; a high frame rate, such as in surgical and 3D imaging; or high spatial resolution, such as in mammography or dental imaging. Some applications also relate to those where the energy of each X-ray photon is measured, notably bi-energy imaging (bone densitometry, angiography, security applications such as baggage screening at airports).

[0047] By "conversion crystal," it should be understood that one or more crystals produce, for example, an electrical response when photons or charged or uncharged particles pass through them. Depending on the application and their physical nature, the crystals composing the conversion layer may also be chosen for their ability to absorb energetic radiation such as X-rays, gamma rays, or charged or uncharged particles, and convert them into another, more easily measurable form of radiation.

[0048] The term crystal is equivalent to the term "crystal layer" and represents a single-crystal or polycrystalline layer. A single-crystal layer is thus made up of a single grain with a single crystal orientation. A polycrystalline layer is made up of an assembly of grains with different crystal orientations.

[0049] By "liquid method," it is understood that the conversion crystal is obtained from at least one element dissolved in at least one solvent, the whole being in a liquid form referred to hereafter as the "liquid precursor." By varying parameters such as the temperature of the liquid precursor, it is possible to promote the growth of the conversion crystal.

[0050] The conversion crystal to be manufactured can be a hybrid perovskite combining an organic part and an inorganic part such as CH3NH3PbBr3. It can also be a completely inorganic perovskite with the general chemical formula ABX3, or mixed compositions such as A(1)i_(y2+...+yn)A(2)y2--•A(n'ynB(1'i.(Z2+...+zm)B(2'z2.. .B(m)zmX(1) 3 (x2+...+xp)X(2)X2. • -X^kp respecting the rule of electronic neutrality, with A and B cations, X an anion, and n, m, p integers. Some examples of compositions are given below: MAPbI3, MAPbCl3, MAPbI3 xBrx, MAyGAi yPbI3, FAPbBr3, CsPbBr3, Cs2AgBiBr6, CsFAPbI3, CsyFAi yPbI3 xBrx, Csi y zMAyFAzPbI3 xBrx. MA corresponds to methylammonium [CH3NH3]+. FA corresponds to formamidinium [HC(NH2)2]+ and GA corresponds to guanidinium [C(NH2)3]+. The conversion crystal to be fabricated, whose formula is explained above, can also be doped with ionic or non-ionic, organic or inorganic impurities. The conversion crystal to be fabricated can also be formed according to other compositions resembling perovskites known by the following names in established Anglo-Saxon terminology: "vacancy-ordered double perovskite," "2D layered perovskite," "perovskite-like materials," "defect perovskites," "elpasolites," "double perovskite." Finally, other types of materials can compose the conversion crystal, such as Ruddlesden-Popper, Dion-Jacobson, Chalcogenide, or Ru-dorffite materials.

[0051] The solvent used may be a mixture of solvents. The solvent is preferably polar and aprotic. It may be, for example, N,N-dimethylformamide, dimethyl sulfoxide, gamma-butyrolactone, acetonitrile, or N-methyl-2-pyrrolidone. It may also be an aqueous solution of hydrogen halide.

[0052] The process of the invention comprises a first step a) consisting of providing a germination crystal 20 whose nature, i.e., composition and crystalline phase, allows the growth of the conversion crystal 30 to be manufactured. The germination crystal 20 may be a crystal of the same composition and crystalline phase (homoepitaxy) as those of the conversion crystal 30. The germination crystal may also be of a different nature than that of the conversion crystal to be grown (heteroepitaxy). In the case of the variant of growth from several germinations, these germinations may be of the same or different natures.

[0053] In one example, the germination crystal 20 is solid. This advantageously allows it to be reused or recycled several times.

[0054] The thickness of the germination crystal 20 must be greater than the thickness of the conversion crystal 30 to be manufactured.

[0055] In one example, the nucleation crystal 20 is formed by assembling several small nucleation crystals 20 into a single nucleation crystal 20 of the desired dimensions. This configuration has the advantage of being technically easier to achieve because it is easier to obtain small nuclei of well-calibrated size and quality than long, highly elongated nuclei. It is thus possible to obtain a row of nuclei pressed against each other, all of whose faces and edges are masked except for those faces in contact with one of the other crystals. In this case, the different growth fronts of each nucleus will meet to form a dense, photoelectric crystalline layer with grain boundaries.

[0056] In the case where the starting seed, i.e. the germination crystal 20, is a single-crystal block, the layer that will grow is also single-crystal (i.e. without grain boundaries). On the other hand, if we start from an assembly of several small germination crystals 20, the layer that we will grow will be polycrystalline and will have grain boundaries, especially at the junction front of the different small germination crystals 20.

[0057] The process also includes a step b) consisting of forming a growth mask 12 on the germination crystal 20.

[0058] The growth mask 12 is configured to prevent the growth of the conversion crystal 30 to be manufactured at the location where the growth mask 12 is formed on the germination crystal 20. The growth mask 12 is formed so as to cover an upper edge 20b of the germination crystal 20. As illustrated in Figures 1, 2, 4 and 6, this upper edge 20b is arranged distally with respect to the support face 1la of the substrate 11 on which the germination crystal 20 is positioned in step c).

[0059] The part of the growth mask covering the upper edge 20b corresponds to the masking of at least one area having a height of at least 10 micrometers measured from the upper edge 20b towards the substrate 11, this height preferably being at least 100 micrometers and ideally on the order of a few hundred micrometers.

[0060] In the following text, the term "edge" means an acute or angular portion of the germination crystal 20 or areas comprising changes of planes or an angle zone between two faces of different crystalline orientations.

[0061] As illustrated in Figures 1, 2, 4 and 6, the growth mask 12 also covers part of the germination crystal 20 except for at least one growth opening 12a delimited in the growth mask 12. In other words, all the faces of the germination crystal 20 that are not to undergo further growth must not be in contact with the liquid precursor.

[0062] The material composing the growth mask 12 is, during the growth of the conversion crystal, brought into contact with a growth solution, otherwise known as a liquid precursor 40. It must therefore be resistant to this liquid precursor 40 under the temperature and pressure conditions used. The growth mask 12 can be formed using organic materials, inorganic materials, or a mixture of both, such as parylene or parylene C, a photolithography resin such as an orthogonal resin, BCB or SU8, silicone, a thermally or ultraviolet-curable material such as epoxy or acrylate compounds, a fluorinated solvent (CYTOP©), a layer of Al2O3, SiO2, or even a metallic layer (Cr, Cu, Pt).The growth mask 12 can be made in one layer, or several layers superimposed or placed next to each other so as to cover the germination crystal 20 avoiding any apparent area outside said opening of. growth 12a.

[0063] The deposition can be carried out by liquid means, such as spraying, dipping, slot-die deposition, inkjet deposition, 3D printing, or brush deposition, or by vacuum techniques such as evaporation, spraying, ALD (Atomic Layer Deposition), chemical vapor deposition, or any other technique known to those skilled in the art. The thickness of the growth mask 12 is greater than 10 nanometers, preferably greater than 100 nanometers, and even more preferably greater than 1 micrometer. The thickness of the growth mask 12 is preferably sufficient to prevent the liquid precursor 40 from coming into contact with certain areas of the nucleation crystal 20 in order to avoid initiating unwanted growth from the nucleation crystal 20. The growth aperture 12a is either present immediately upon deposition of the growth mask 12 or obtained after deposition of the growth mask 12.In the latter case, the growth opening 12a is obtained either by so-called additive techniques by not masking this area during the deposition of the growth mask 12, or by so-called subtractive techniques such as laser ablation, photolithography, etching, or the lift-off technique well known to those skilled in the art.

[0064] If the germination crystal 20 were not masked, the growth of the conversion crystal would occur in all directions except on the face to which the germination crystal is attached. In particular, the forming conversion crystal would also grow in the direction perpendicular to the plane of the substrate 11, which would make it impossible to precisely control both the thickness of the conversion crystal and the surface area of ​​the substrate to be covered.

[0065] In one example, the growth mask 12 can also have the function of an adhesive in order to mechanically hold the germination crystal 20 on the substrate 11.

[0066] In an example illustrated in [fig. 1], one face of the germination crystal 20 in contact with the substrate 11 is not covered by the growth mask 12. This configuration must nevertheless ensure that the liquid precursor 40 does not penetrate between the germination crystal 20. Thus, parasitic growth cannot occur.

[0067] As illustrated in Figures 1, 2, 4 and 6, the manufacturing process further includes a step c) which consists of positioning the germination crystal 20 on the support face 1la of the substrate 11. This positioning is entirely constrained by two imperatives.

[0068] First, the germination crystal 20 must be oriented so that the direction perpendicular to a plane corresponding to a face of a crystal plane 20d, corresponding to a stable growth orientation face, is parallel to the supporting face To implement this condition, the germination crystal may have, on its external face oriented opposite to the support face 1la, an orientation different from the orientation of the crystal plane 20d corresponding to a stable growth orientation face; the positioning of the germination crystal 20 will nevertheless allow the object of the invention to be realized as long as the orientation of the crystal plane 20d corresponding to the stable growth orientation face is parallel to the support face 1la. In other words, the crystal plane 20d corresponding to the stable growth orientation face can be arranged inside the germination crystal 20, regardless of the orientation of the apparent external face of the germination crystal 20. In particular, it is irrelevant whether the apparent external face has defects or is cut.

[0069] In other words, the stable growth orientation face is a face in which several periodic bond chains run. The corresponding crystal planes are necessarily crystal planes that are generally dense planes, therefore with low Miller indices h,k,l < 3.

[0070] An equivalent means of implementing this first condition is to position the crystal plane 20d corresponding to a stable growth orientation face on the side of the support face 1la and parallel to the support face lia. Thus, even if the nucleation crystal has, on its external face oriented towards the support face lia, a different orientation from the orientation of the crystal plane 20d corresponding to the stable growth orientation face; the positioning of the nucleation crystal 20 will make it possible to achieve the object of the invention as long as the orientation of the crystal plane 20d corresponding to the stable growth orientation face is parallel to the support face lia.

[0071] Next, the positioning of the nucleation crystal 20 must be such that at least one of its growth faces 20a is present and arranged transversely to the support face of the substrate 11. The term "transversely" means that the growth face 20a forms an angle with the substrate 11 as close as possible to 90°. In one example, a crystal having a cubic crystallographic structure can make it possible to obtain this angle.

[0072] The orientation of the growth face 20a advantageously ensures that large areas can be covered.

[0073] In one example, in step c), the orientation of the germination crystal 20 is precisely determined, typically to within 1°, or preferably to within 0.1° or 0.01°. The crystallographic orientation of the germination crystal 20 can be easily controlled, even when the external face of the germination crystal 20a has a different orientation from the orientation of the crystal plane 20d corresponding to the stable growth orientation face, by performing X-ray diffraction characterizations, of the Laue type, 0 / 20, or of the "rocking curve" type according to Anglo- Saxon consecrated. Mechanical parts can also be used to adjust the orientation of the germination crystal 20 relative to the surface of the substrate 11.

[0074] In a particular case of the invention, the orientation of the germination crystal is different from 90°. This allows the conversion crystal to grow by inducing a continuous thickness gradient, increasing or decreasing, as the conversion crystal advances on the surface and during growth.

[0075] In a further example, the germination crystal 20 and the conversion crystal 30 to be manufactured have a cubic crystal system.

[0076] In this example, the growth face 20a has as a crystallographic orientation a plane of type {1,0,0} or of type {1,1,0}.

[0077] In this example, if the growth face has a crystallographic orientation of (100), the 20d crystal plane can be, among others, the plane associated with the stable growth face of orientation (010) or (001). If the growth face has a crystallographic orientation of (110), the 20d crystal plane can be, among others, the plane associated with the stable growth face of orientation (-110). In other words, it is necessary to choose, from among all possible stable faces, a growth face with Miller indices (hkl) and a perpendicular face with different Miller indices (abc). In this example, since the structure is cubic, any pair of stable faces whose indices satisfy the relation h.a+k.b+lc=0 can be selected.

[0078] However, all crystal orientation pairs giving rise to stable crystal faces, such that a first crystal plane 20d of the germination crystal 20 is parallel to the support face 1la and such that at least one growth face 20a of the germination crystal 20 is arranged transversely to the support face of the substrate 11, are conceivable within the framework of this invention.

[0079] In one example of implementation of the manufacturing process, the germination crystal 20 is composed of several germs assembled together.

[0080] The germination crystal 11 can be fabricated in a single block using conventional self-supporting single-crystal growth techniques. Its surface can optionally be treated mechanically, for example by polishing and / or cutting to the correct dimensions, and / or chemically. It is also possible to use a solvent to adjust the surface finish of the germination crystal and / or to use one or more physical treatments, for example with plasma or laser, on each initial growth face of the seed, so as to intentionally generate defects that will promote resumption of growth.

[0081] In a particular case of the invention, the germination crystal 20 can grow directly from the surface of the substrate.

[0082] As illustrated in Figures 2, 3 and 6, the process according to the invention also includes a step d) which consists of applying the liquid precursor 40 of the crystal ofConversion 30, from the support face 1la of the substrate 11 to at least the level of the flat, smooth portion of the growth face 20a, to obtain free growth of the conversion crystal 30, from the flat, smooth portion of the growth face 20a, with a growth thickness 30b contained between the support face 1la of the substrate 11 and an upper edge 12b of the growth opening 12a arranged distally to the support face 1la of the substrate 11. The term "distal" means equivalently that the upper edge 12b is arranged opposite the substrate 11. The upper edge 12b can have any shape induced by the way the crystal is masked. In one example, the upper edge 12b is serrated or crenellated to obtain a suitable topology of the upper surface of the forming crystal. However, it is necessary that the cutting of the upper edge 12b be such that it allows the growth of stable faces.In the example of a crenellated cut, the vertical parts of the crenellations must correspond to stable faces, as must the horizontal part of the crenellations.

[0083] The growth thickness 30b can be slightly greater than the growth opening 12a. Indeed, in the case where the growth mask 12 covers the lower edge 20c of the germination crystal 20, the growth perturbations induced in this area close to the substrate cause the germination crystal to tend to grow until it reaches the substrate 11. Nevertheless, the upper facet of the conversion crystal in formation remains flat.

[0084] In the following text, "free growth" means growth without mechanical constraint. Thus, free growth differs from the growth of a crystal or polycrystal constrained between two walls, mechanically leaving only one or two opposing growth directions possible. This is advantageous for obtaining a very flat and uniform surface, corresponding to stable crystal faces.

[0085] In the rest of the text, the term “growth” refers to a formation, a ho-moepitaxis, a heteroepitaxis or a crystallization.

[0086] The term “substrate” can refer either to an inert surface, or to all or part of an electronic or optoelectronic device.

[0087] The substrate 11 can be passive, acting as a simple support, or it can be active, i.e., have additional functionality. In particular, the substrate 11 can comprise an active matrix, for example with transistors, or a passive matrix, such as with discrete pixels without transistors. In the case where the matrix is ​​active, it is possible to use many existing known transistor technologies (a-Si, IGZO, organic transistors, polycrystalline silicon). It is also possible to use so-called CMOS technologies, which allow the integration of numerous transistors within a single pixel and the performance of signal processing at the pixel level. The use of CMOS is particularly advantageous in X-ray and gamma-ray spectrometry applications. The substrate 11 can be, for example, made of glass, plastic such as polyimide, PET, PEN, or even silicon-based.

[0088] The surface of the substrate 11 can be pre-prepared to ensure proper adhesion of the conversion crystal 30 to the substrate 11. Similarly, the substrate 11 can be prepared to ensure contact at the molecular level between the conversion crystal and the support face lia. For example, the perovskite conversion crystal may exhibit a strong chemical affinity for the support face lia, which represents a surface of a conducting electrode in an optoelectronic device, in order to facilitate charge transfer from one to the other. The adhesion of the conversion crystal 30 to the substrate 11 is ensured by covalent bonds, ionic bonds, or Van der Waals forces between the conversion crystal 30 and all or part of the surface of the substrate 11, or by the roughness and topology thereof.In particular, the lateral growth mode obtained via the manufacturing process described in this document allows the growth front to grow progressively and in intimate contact with the surface of the substrate 11, which promotes adhesion to this surface.

[0089] In one example, the adhesion of the conversion crystal 30 to the surface of the substrate 11 is ensured mechanically via the topology and roughness of the surface, or chemically via the presence of suitable chemical groups on the surface by self-assembled monolayers known under the Anglo-Saxon terminology "Self-assembled monolayers" of the aminopropyltriethoxysilane (APTES) or cysteamine type. It can also be a mixture of these different possibilities.

[0090] The surface of the substrate 11 is preferably flat, but it may, if necessary, have a curved or inclined surface, or any non-planar configuration. In this case, since the upper facet 30a of the conversion crystal 30 is a flat crystalline face, the growth obtained via the manufacturing process described herein involves a variation in the thickness of the conversion crystal 30 that follows the curvature of the side in contact with the substrate 11.

[0091] Generally, at least one growth opening 12a is arranged at the growth face 20a so that only a flat and smooth portion of the growth face 20a is able to be in contact with the liquid precursor 40 of the conversion crystal 30.

[0092] All geometries of the growth opening 12a can be considered, such as square or rectangular. However, it is important to ensure that the germination crystal 20 is large enough to cover the entire area of ​​interest in the substrate.

[0093] In the following text, a flat and smooth portion of the growth face corresponds to a natural face of the crystal and which does not include an edge. In other words, it must be a portion of a face present in the morphology of crystal 30 in the growth conditions used (solvent, temperature).

[0094] In one example, the portion of the crystal transverse to the flat and smooth portion of the growth face 20a does not depolarize the light.

[0095] When the liquid precursor 40 is in the undersaturated state, the solute concentration of the conversion crystal 30 is below the solubility limit of the solute in the conversion crystal in the liquid precursor 40. This state allows the growth face of the nucleation crystal 20 to dissolve slightly at the growth opening 12a. Thus, surface defects (chips, stresses, contaminants) are dissolved before a subsequent growth phase occurs.

[0096] Conversely, when the liquid precursor 40 is in the supersaturated state, the growth face 20a can grow to form the conversion crystal 30. For this, the concentration of conversion crystal 30 dissolved in the liquid precursor 40 must be slightly higher, at least on the order of 0.5 to 1%, than the solubility limit of the conversion crystal 30 dissolved in the liquid precursor 40. In this state, the crystallization of the conversion crystal from the growth face at the growth opening 12a is spontaneous.

[0097] The state of undersaturation or supersaturation is generally controlled by temperature, the concentration of conversion crystals 30, the nature of the solvent, the use of a non-solvent, or pressure. The conditions enabling growth are conventional and known to those skilled in the art. When temperature is used as a parameter, crystallization can be achieved by increasing the temperature in the case of retrograde solubility, or by decreasing the temperature in the case of direct solubility, or by maintaining constant temperature and concentration to achieve an adequate level of supersaturation.

[0098] The conditions enabling growth are known to those skilled in the art, for example by varying the solution temperature as illustrated in [Fig. 5] or by using a non-solvent. Directed growth relies on controlling the applied supersaturation so that only screw dislocation growth is active, which corresponds to a spiral growth mode. Thus, only screw dislocations originating from the growth face 20a, at the growth opening 12a, are active and allow growth. In order to achieve growth exclusively by screw dislocation, it is necessary, on the one hand, to ensure a sufficient level of purity to prevent growth blocking by impurities with lower supersaturation and, on the other hand, to limit the supersaturation to prevent 2D nucleation growth.

[0099] An example of conditions suitable for the manufacturing process of the invention is given below. A single-crystal nucleation crystal 20 having flat, smooth faces that do not depolarize light is selected. This nucleation crystal 20 is The substrate is bonded to a silicon substrate with silicone adhesive. The substrate is bonded to the bottom of a glass reactor with the same silicone adhesive. The germination crystal 20 is covered with the growth mask 12, except at a growth opening 12a. A liquid precursor 40 of MAPbBr3 at 1 mol / L is obtained by dissolving the precursors PbBr2 and MABr in a 1:1 ratio at room temperature in N,N-Dimethylformamide. The germination crystal 20 and the liquid precursor 40 are temperature-adjusted separately for a period of 1 h at a temperature of 55°C. The heated liquid precursor 40 is then poured onto the germination crystal 40. The substrate 11 is in a horizontal position. The growth of the conversion crystal 30 is carried out in the liquid precursor 40 between 58°C and 70°C, following the temperature profile shown in [Fig. 5].The liquid precursor 40 is for example stirred using a propeller or renewed and set in motion by a device described in [fig.7].

[0100] In the example illustrated in [Fig. 7], the liquid precursor 40 can be obtained by dissolving a feedstock, for example an excess of solid perovskite, in a reaction chamber, which can be an accumulator 70. A constant temperature difference is then maintained between the accumulator 70 and a reactor containing the substrate 11 and the nucleation crystal 20. The liquid precursor 40 is drawn off by a pumping system 71 and then filtered by a filtration system 72 before being fed into the reactor. The liquid precursor 40 is then recirculated back to the accumulator 70, and so on, in a closed-loop system. The retentate 73 retained by the filtration system 72 is reintroduced into the accumulator 70.Combined with the manufacturing process described above, these arrangements allow the entire feedstock dissolved in the accumulator 70 to be deposited on the substrate 11 in the form of the conversion crystal 30, which implies a saving in manufacturing cost.

[0101] It is advantageous to ensure efficient renewal of the solution in contact with the conversion crystal 30. Indeed, this limits boundary layer phenomena which, for large dimensions, lead to growth instabilities, by step packing or step swerving, conducive to the formation of structural defects detrimental to optoelectronic performance and to growth instabilities, in particular at the junction between the substrate 11 and the growing face of the conversion crystal 30, which degrades the mechanical and / or chemical contact between the conversion crystal 30 and the surface of the substrate 11.

[0102] In one example, during step d), the growing conversion crystal 30 comprises a planar upper facet 30a parallel to the support face 1la and whose dislocations are inactive.

[0103] Non-active dislocations are, for example, of the wedge type or of a screw character but not being perpendicular to the upper facet 30a. They do not allow the growth of the crystal.

[0104] Active dislocations are screw-like dislocations perpendicular to the growth face. They constitute walking sources that provide solute incorporation sites and are therefore favorable to crystal growth.

[0105] Thus, thanks to the manufacturing process described in this document, the conversion crystal 30 comprises, from the outset and throughout its growth, a naturally flat upper facet 30a, parallel to the support face and without active dislocations, i.e., whose dislocations are solely inactive. This makes it possible to control the thickness of the resulting conversion crystal 30 by maintaining it at the height of the upper edge 20b of the growth aperture 12a. Indeed, inactive dislocations do not allow growth to resume, and the thickness of the crystal therefore does not increase during its growth. This is advantageous for very precisely controlling the thickness of the resulting conversion crystal 30 and, consequently, the amount of radiation absorbed by the conversion crystal 30 when it is installed in an optoelectronic device.

[0106] The conversion crystal 30 obtained via the manufacturing process described above contains screw dislocation defects whose line is parallel to the growth direction, in a plane parallel to the substrate 11. These dislocations will be perpendicular to the direction of charge drainage in the devices, which is the direction in the thickness of the conversion crystal 30. Insofar as these dislocations can be a source of ionic migration in perovskites, the configuration thus obtained is very favorable for avoiding ionic migration phenomena in the thickness of the conversion crystal 30, and thus limiting electrical instabilities.

[0107] The thickness of the conversion crystal 30 is primarily controlled by the size of the growth aperture 12a. The conversion crystal 30, once formed, preferably has a thickness greater than 1 micrometer, preferably greater than 100 micrometers, and even more preferably greater than 300 micrometers. In the case of direct conversion X-ray detectors, the thickness of the conversion crystal 30 to be fabricated is defined so as to absorb the greatest possible portion of the incident radiation at the energy targeted for the application.For example, to absorb X-rays equivalently to 600 micrometers of Csl, which is today the most widely used converter material in medical radiography (85% X-ray absorption at RQA5 and 50% at RQA9), it is necessary to form a conversion crystal 30 with a thickness of 600 micrometers in CH3NH3PbI3 or 1300 micrometers in CH3NH3PbBr3 at RQA 5 (X-ray spectrum centered on 50keV according to standard IEC62220-1), or a thickness of 450 micrometers in CH3NH3PbI3, or 800 micrometers in CH3NH3PbBr3 at RQA9 (X-ray spectrum centered on 70keV according to standard IEC62220-1). IEC62220-1 standard).

[0108] In an example illustrated in [Fig. 2], the process includes the additional step d0), which consists of configuring the liquid precursor 40 of the conversion crystal 30 so that it is in a state of undersaturation at least at the level of the flat and smooth portion of the growth face 20a. Step d0) is carried out before step d). This makes it possible to slightly dissolve the growth face of the germination crystal 20 at the growth opening 12a. Thus, a defect-free surface is advantageously obtained before carrying out a subsequent growth phase according to step d).

[0109] According to one example of the manufacturing process, in step b), the growth mask 12 is further formed so as to cover a lower edge 20c of the germination crystal 20 arranged proximally with respect to the support face 1la of the substrate 11. These arrangements are advantageous because, otherwise, the growth of the conversion crystal is disturbed and may lead to a polycrystal instead of the expected single crystal.

[0110] In one example, the length of the germination crystal 20 is greater than or equal to the lateral dimension of the area of ​​the substrate 11 to be covered. However, as shown in [Fig. 3], it is also possible to consider the case where the length of the germination crystal 20 is less than the lateral dimension of the area of ​​the substrate 11 to be covered. In this case, it is possible to mask only certain areas of the germination crystal 20 so that the conversion crystal 30 ultimately covers the appropriate surface of the substrate 11.

[0111] In one example of the process, the upper edge 12b of the growth opening 12a is parallel to the support face 1la of the substrate 11. This configuration allows control of the flatness of the conversion crystal 30 and therefore the homogeneity of radiation conversion yield.

[0112] In an example illustrated in [Fig. 6], during step b), an additional growth opening 12a is arranged on a face of the germination crystal 20 opposite the growth face 20a. It follows that, as a result, the face of the germination crystal 20 opposite the growth face 20a is also a stable growth face. Thus, the conversion crystal 30 can grow in two opposite directions. This makes it possible to increase production rates and further reduce costs. More generally, more than two growth openings can be arranged so as to grow the crystal in several directions relative to the initial seed.

[0113] According to one example of the manufacturing process, during step b), the growth mask 12 is formed by an adhesive 60. The adhesive may be inert with respect to the germination crystal 20. As illustrated in [Fig. 4], the adhesive 60 may extend beyond the germination crystal 20 so as to completely cover the face of the germination crystal. mination 20 arranged opposite the support face 1 of the substrate 11.

[0114] In an example of the process illustrated in [Fig. 5], during step d), the temperature of the liquid precursor 40 of the conversion crystal 30 is gradually increased over time. This maintains the solution in a state of supersaturation most favorable to growth and thus reduces the content of crystalline defects in the growing conversion crystal 30.

[0115] In one example of the process, during step c), the germination crystal 20 is positioned so that it is offset from an area 50 of the substrate 11 where the conversion crystal 30 to be produced is formed. This is advantageous for homogeneously covering a specific area of ​​the substrate 11.

[0116] In an example illustrated in [Fig. 3], the manufacturing process includes a step f) carried out after step d). Step f) consists of treating the conversion crystal 30 so as to make the germination crystal 20 and the conversion crystal 30 independent after the formation of the crystal 30. Thus, at the end of growth, the germination crystal 20 can be left on the surface and / or removed from the surface by mechanical or physical (laser) cutting and / or by peeling it away from the surface of the substrate 11.

[0117] In an example illustrated in [fig.3], the process includes step e) which is carried out after step d). Step e) consists of treating the conversion crystal 30 so as to make at least one of its faces straight.

[0118] In a further embodiment of the invention, the masking step (b) can be repeated several times. In other words, once step (b) has been carried out once, steps (c) and (d) are performed to obtain a first portion of the conversion crystal 30. Growth is then stopped. The conversion crystal 30 thus obtained then serves as the germination crystal 20 in a further iteration of step (a). The conversion crystal 30 is then masked in a further step (b), and the rest of the process is repeated. It is thus possible to repeat the process several times. This technique makes it possible to avoid the generation of defects on the upper facet 30a during excessively long growth times, and to prevent these defects from inducing growth in the direction normal to the substrate 11 and the support face 1a.In this implementation, growth is stopped before these defects form, a new mask is formed and growth is then restarted following steps c) and d). This approach implies that the mask is removed from the upper facet 30a at the end of the process.

[0119] Thus, once the conversion crystal 30 is obtained, its surface can be treated mechanically or chemically, for example by chemical polishing, and / or chemically, for example by solvent cleaning, chemical grafting to modify the surface condition, and / or physically by UV-O3 or plasma treatment. It is For example, it is possible to repolish the top face of the crystal 30 to ensure better homogeneity of the thickness of the conversion crystal 30 over the entire surface of the substrate 11. In some cases, the edges of the conversion crystal 30 can be cut to obtain the desired lateral dimensions.

[0120] An optoelectronic device, not shown, can be fabricated from the conversion crystal 30 obtained by the fabrication process described above. To fabricate this optoelectronic device, an upper electrode is deposited on the conversion crystal 30. Preferably, the upper electrode is deposited continuously over at least the entire surface of the active matrix covered by the conversion crystal 30. In one example, a single upper electrode is common to all the pixels of the matrix. This electrode may be of the same material as the lower electrode constituting the portion of the substrate 11 on which the conversion crystal 30 is obtained, or of a different material, as in a photodiode device. It is possible to use metals (Au, Cr, Pt, Pd, Ag), conductive oxides (ITO, AZO, GZO), conductive organic materials (PEDOT-PSS, PANI, graphene, carbon ink), or a combination of these materials.It is also possible to use one or more interface layers on the electrode to fix the output work and chemical compatibility with the perovskite (PEIE, C60, MoO3, V2O5, BCP, SPIRO). The upper electrode is then electrically connected to the external circuit, for example by means of a conductive wire or a printed conductive line.

[0121] The conversion crystal 30 can finally be encapsulated in air, or in an inert atmosphere (N2, Ar), or in an anhydrous atmosphere. This can be achieved using a glass cap bonded to a surface of the substrate 11, which is not covered by the conversion crystal 30, using a bead of adhesive, or using an adhesive such as a glue or a pressure-sensitive adhesive and a plastic film having barrier layers. The encapsulation is transparent or opaque to visible light, but allows the radiation to be detected to pass through.

[0122] The contact points of the pixel array are then connected to readout electronics using flexible cables and ACF (Anisotropic Conductive Film) adhesives. The array can be characterized using standard pixel imager readout methods.

Claims

Demands

1. A liquid-oriented manufacturing process for a conversion crystal (30), the process comprising the following steps: a) provide a germination crystal (20) enabling the growth of the conversion crystal (30) to be manufactured; b) form a growth mask (12) on the germination crystal (20), the growth mask (12) being configured to prevent the growth of the conversion crystal (30) to be manufactured at the location where the growth mask (12) is formed on the germination crystal (20), the growth mask (12) being formed so as to cover on the one hand an upper edge (20b) of the germination crystal (20) arranged distally with respect to a support face (1la) of a substrate (11) on which the germination crystal (20) is positioned in step c), on the other hand a part of the germination crystal (20) with the exception of at least one growth opening (12a) delimited in the growth mask (12); c) position the germination crystal (20) on the support face (1la) of the substrate (11) so that the germination crystal (20) is oriented so that a first crystal plane (20d), corresponding to a stable growth orientation face of the germination crystal (20), is parallel to the support face (1la) and so that at least one growth face (20a) of the germination crystal (20) is arranged transversely to the support face of the substrate (11), the growth opening (12a) being arranged at the level of the growth face (20a) so that only a flat and smooth portion of the growth face (20a) is able to be in contact with a liquid precursor (40) of the conversion crystal (30); d) apply the liquid precursor (40) of the conversion crystal (30) configured in a state of relative supersaturation at least at the level of the flat and smooth portion of the growth face (20a) to obtain free growth of the conversion crystal (30), from the flat and smooth portion of the growth face (20a), according to a growth thickness (30b) contained between the support face (1la) of the substrate (11) and a top edge (12b) of the growth opening (12a) arranged distally with respect to the support face (1la) of the substrate (11).

2. A method for manufacturing a conversion crystal (30) according to claim 1, wherein the method comprises the additional step next: dO) configure the liquid precursor (40) of the conversion crystal (30) so that it is in a state of undersaturation at least at the level of the flat and smooth portion of the growth face (20a), step dO) being carried out before step d).

3. A method for manufacturing a conversion crystal (30) according to any one of claims 1 or 2, wherein, during step d), the growing conversion crystal (30) comprises a planar upper facet (30a), parallel to the support face (lia), and whose dislocations are inactive.

4. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 3, wherein, during step c), the orientation of the germination crystal (20) is achieved to within at least 0.1°.

5. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 4, wherein, during step b), the growth mask (12) is formed so as to cover a lower edge (20c) of the germination crystal (20) arranged proximally with respect to the support face (1la) of the substrate (11).

6. Method of manufacturing a conversion crystal (30) according to any one of claims 1 to 5, wherein the upper edge (12b) of the growth aperture (12a) is parallel to the support face (lia) of the substrate (11).

7. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 6, wherein, during step b), at least one additional growth opening (12a) is arranged on at least one additional growth face (20a) of the germination crystal (20) arranged transversely to the substrate support face (H).

8. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 7, wherein the germination crystal (20) and the conversion crystal (30) to be manufactured have a cubic atomic structure.

9. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 8, wherein the conversion crystal (30) to be manufactured is a perovskite of type ABX3, A'2C1+D3+X6, A2B4+X6 or A3B23+X9 with A, A', C, D and B being cations and X an anion; A, B, C, D, X being a single element or a mixture of at least two elements.

10. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 9, wherein the conversion crystal (30) to be manufactured is an organic-inorganic hybrid perovskite of formula A(*', / ,A® A® ,B® B®' X(*h / ,X® ivjitiiuii / rt l-(y2+...+yn)-rk yn-*-* 1-(22+.. .+2111)-1^ 22^^-° 2in7Y 3-(x2+...+xp)yv x2.. .X®xp, respecting the electronic neutrality rule, with A(n) and B® cations, X(n) an anion and n, m, p integers.

11. Method of manufacturing a conversion crystal (30) according to any one of claims 1 to 10, wherein the growth face (20a) has a crystallographic orientation of a {1,0,0} plane or a {1,1,0} plane.

12. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 11, wherein, during step b), the growth mask (12) is formed by an adhesive (60).

13. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 12, comprising the following step, carried out after step d): e) treating the conversion crystal (30) so as to make at least one of the faces of the conversion crystal (30) straight.

14. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 13, wherein the germination crystal (20) is composed of several seeds assembled together.

15. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 14, wherein, during step d), the temperature of the liquid precursor (40) of the conversion crystal (30) is changed gradually over time.

16. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 15, wherein, during step c), the positioning of the germination crystal (20) is carried out so that the germination crystal (20) is offset from an area (50) of the substrate (11) where the conversion crystal (30) to be manufactured is formed.

17. A method for manufacturing a conversion crystal (30) according to any one of claims 1 to 16, comprising the following step carried out after step d): f) treating the conversion crystal (30) so as to make the germination crystal (20) and the conversion crystal (30) independent of each other.

18. An optoelectronic device comprising a conversion crystal obtained by growth in the optoelectronic device and according to one of the re- claims 1 to 17, in which the conversion crystal has a thickness greater than or equal to 100 micrometers.

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