FR3116153A1 - Process for the oriented manufacture of a conversion crystal by liquid means - Google Patents

Abstract

A method of liquid oriented conversion crystal (30) fabrication comprising the steps: a) providing a seed crystal (20); b) forming a growth mask (12) on the seed crystal (20; c) positioning the seed crystal (20) such that the seed crystal (20) is oriented so that a first crystal plane (20d) , either parallel to a support face (11a) of a substrate (11) and so that at least one growth face (20a) of the seed crystal (20) is 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 flat and smooth portion of the growth face (20a) to obtain free growth of the conversion crystal (30). Figure 2

Description

Process for the oriented manufacture of a conversion crystal by liquid means

Disclosed is a method for manufacturing a conversion crystal by a liquid process.

STATE OF THE PRIOR ART

In the field of ionizing radiation detectors (X-rays, gamma, charged or uncharged particles of the alpha, beta, protons, neutrons type, etc.), it is important to detect the quantity of radiation received as accurately as possible, ideally for an acceptable cost. . It is thus very advantageous to obtain a layer of conversion crystal having a high thickness, that is to say greater than 1 micrometer, or even greater than 100 micrometers in order to effectively absorb the incident radiation. This makes it possible to measure a large quantity of radiation without it succeeding in passing through the conversion crystal. This radiation is converted directly into electrical charges. This is referred to as a direct conversion detector. For measurement quality and reliability, it is also important that the conversion crystal layer has a crystallinity close to that of a single crystal and with a high density to limit the ability of radiation to be able to pass through the conversion crystal layer. . For many applications, such as radiography, the surface of the layer must be several tens or even several hundred square centimeters.

In this context, it is known to carry out deposits by liquid means, for example by spinner centrifugation or by methods known under the Anglo-Saxon terminology “slot-die” or “doctor blade”. These methods are suitable for obtaining thin layers whose thickness is less than 1 micrometer, but they do not allow obtaining layers having thicknesses greater than several tens of micrometers while keeping a crystalline structure closest to a single crystal.

Several coupling techniques on a surface of thick layers of perovskites, by liquid means, have nevertheless already been proposed.

Thus the document “Kovalenko, Nat. Photo. 9 (2015) 444” describes a spray-coating deposition method for depositing a thick layer (10-100 micrometers) of CH ₃ NH ₃ PbI ₃ (MAPI) on a surface with a metal electrode to produce a detector device. This process is difficult to control on layers greater than 100 micrometers. Moreover, the layers obtained have a poorly controlled and very polycrystalline morphology, with many grain boundaries, which is not favorable for the optoelectronic properties. The thickness and the surface condition are also difficult to control.

The document “Nature 550 (2017) 87” proposes a technique for depositing thick layers by liquid means. They use an ink of MAPI microparticles suspended in a solvent. These microparticles are then deposited on the surface (for example on an active transistor matrix) by coating. After removal of the solvent, the layer consists of an agglomerate of microparticles (whose typical dimensions are of the order of 30 micrometers) which percolate with each other. 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. In addition, due to the porosity, the layer is less dense, which is not favorable for the absorption of energetic radiation (X, gamma).

The document "WO 2017/046390 A1" proposes to deposit a first perovskite layer (nucleation layer) on the surface of the substrate, then to grow, in solution, a second layer of perovskite, thicker, from the first layer. . The technique described requires the use of a nucleation layer different from the layer to be grown, which can cause problems in the case of a detector device by blocking the collection of charge carriers. The layer thus produced is highly polycrystalline (many grain boundaries). Grain boundaries are discontinuous and disturbed areas that can lead to a decrease in performance (area with a higher density of electronic traps, area more favorable to ion migration). Moreover, it is highly probable that the final thickness is very inhomogeneous due to the natural disorientation 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.

The document “Huang J., Nat. Photo. 11 (2017) 315” proposes to grow a monocrystal of MAPbBr ₃ , measuring approximately 1cm in lateral dimension, on a surface by initiating nucleation from a seed placed on the surface. In this configuration, the crystal will not be able to grow laterally on the surface without also growing in the direction normal to the surface, implying an increase in thickness. It is difficult to envisage extending this technique to larger surfaces (greater than a few square centimeters). In the case where several germs would initially be arranged on the surface, the parallel growth of these different germs would pose problems in terms of homogeneity of thickness and disorientation of these germs but also of grain boundaries and strong associated stresses between the crystals.

Finally, the document “Adv. Mater. 2017, 1602639” describes a technique for coupling a thick layer (between 100 and 800 micrometers) of MAPbBr ₃ by confining the growth between two plates describing two opposite surfaces. In it, a covering area of 120 square centimeters is demonstrated. Nevertheless, this technique is difficult to implement because it requires continuous renewal of the growth solution between the two very close plates to continuously feed the growth of the crystal. The final layer shows strong inhomogeneities in thickness and in the number of grain boundaries. However, these two parameters are critical because they directly impact conversion performance.

The present invention aims to respond to all or part of the problems presented above.

In particular, a goal is to provide a solution that meets at least one of the following objectives:

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

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

This object can be achieved thanks to the implementation of a process for the oriented manufacture of a conversion crystal by the liquid route, the process comprising the following steps:
a) providing a seed crystal allowing the growth of the conversion crystal to be manufactured;
b) forming a growth mask on the seed crystal, the growth mask being configured to prevent the growth of the conversion crystal to be fabricated at the location where the growth mask is formed on the seed crystal, the growth mask being formed so as to cover on the one hand an upper edge of the seed crystal arranged distally with respect to a support face of a substrate on which the seed crystal is positioned in step c), on the other hand on a part of the seed crystal with the exception of at least one growth opening delimited in the growth mask;
c) positioning the seed crystal on the support face of the substrate so that the seed crystal is oriented so that a first crystalline plane, corresponding to a stable growth orientation face of the seed crystal, is parallel to the face support and so that at least one growth face of the seed crystal is arranged transversely to the support face of the substrate, the growth opening being arranged at the level of the growth face so that only a flat and smooth portion of the growth face is capable of being in contact with a liquid precursor of the conversion crystal;
d) applying the liquid precursor of the conversion crystal configured in a state of relative supersaturation at least at the level of the planar and smooth portion of the growth face to obtain free growth of the conversion crystal, starting from the planar and smooth portion of the growth face, along a growth thickness contained between the support face of the substrate and an upper edge of the growth opening arranged distally with respect to the support face of the substrate.

Certain preferred but non-limiting aspects of this method of manufacture are the following, taken alone or in combination.

In one implementation of the manufacturing process, the process includes the following additional step:
d0) configuring the liquid precursor of the conversion crystal so that it is in a state of under-saturation at least at the flat and smooth portion of the growth face, step d0) being carried out before step d).

In one implementation of the manufacturing process, during step d), the growing conversion crystal comprises a planar upper facet, parallel to the support face, and whose dislocations are non-active.

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

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

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

In one implementation of the manufacturing method, during step b), at least one additional growth opening is arranged on at least one additional growth face of the seed crystal arranged transversely to the support face of the substrate.

In one implementation of the manufacturing method, the seed crystal and the conversion crystal to be manufactured have a cubic atomic structure.

In one implementation of the manufacturing process, the conversion crystal to be manufactured is an ABX ₃ type perovskite, A' ₂ C ¹⁺ D ³⁺ X ₆ , A ₂ B ⁴⁺ X ₆ or A ₃ B ₂ ³⁺ X ₉ with A, A', C, D and B cations and X an anion; A, B, C, D, X being a single element or a mixture of at least two elements.

In one implementation of the manufacturing process, the conversion crystal to be manufactured is an organic-inorganic hybrid perovskite of formula A ⁽¹⁾ _{1-(y2+…+yn)} A ⁽²⁾ _y2 …A ⁽ⁿ⁾ _yn B ^{( 1)} _{1-(z2+…+zm)} B ⁽²⁾ _z2 …B ^(m) _zm X ⁽¹⁾ _{3-(x2+…+xp)} X ⁽²⁾ _x2 …X ^(p) _xp , respecting the rule of neutrality electronic, with A ⁽ⁿ⁾ and B ⁽ⁿ⁾ cations, X ⁽ⁿ⁾ an anion and n, m, p integers.

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

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

In one implementation of the manufacturing method, the method comprises the following step, implemented after step d):
e) treating the conversion crystal so as to make at least one of the faces of the conversion crystal rectilinear.

In one implementation of the manufacturing process, the seed crystal is composed of several seeds assembled together.

In one implementation of the manufacturing method, during step d), a temperature of the liquid precursor of the conversion crystal is gradually modified over time.

In one implementation of the manufacturing method, during step c), the positioning of the seed crystal is carried out so that the seed crystal is offset with respect to a zone of the substrate where the conversion crystal to be manufactured is formed .

In one implementation of the manufacturing method, the method comprises the following step implemented after step d):
f) treating the conversion crystal so as to make the seed crystal and the conversion crystal independent of each other.

The invention also relates to an optoelectronic device comprising a conversion crystal obtained by growth in the optoelectronic device and according to such a method, in which the conversion crystal has a thickness greater than or equal to 100 micrometers.

Other aspects, objects, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings. on which ones :

There illustrates in schematic sectional view the steps of an example of a method according to the invention where a seed crystal is positioned on a substrate and is covered in part by a growth mask, which does not cover the lower edge of the seed crystal germination.

There illustrates in a schematic sectional view, before and during the growth of the conversion crystal, steps of an example of a method according to the invention where a seed crystal is positioned on a substrate and is partly covered by a growth mask which covers the lower edge of the seed crystal.

There illustrates, in a schematic top view, the steps of an example of a method according to the invention where the seed crystal is first offset with respect to a zone of the substrate where the conversion crystal to be manufactured must be formed then, during of the growth of the conversion crystal, the conversion crystal covers this area and the seed crystal is made independent of the conversion crystal obtained by growth.

There illustrates a cross-sectional view of a seed crystal whose growth mask is made with a glue.

There illustrates a temperature profile applied to the liquid conversion crystal precursor during growth of the conversion crystal.

There illustrates an example of a process according to the invention where, during step b), an additional growth opening is arranged on a face of the seed crystal opposite the growth face.

There illustrates an example of a manufacturing device implementing an example of a manufacturing method according to the invention.

DETAILED EXPLANATION OF PARTICULAR EMBODIMENTS

In the appended FIGS. 1 to 7 and in the remainder of the description, elements which are identical or similar in functional terms are identified by the same references. In addition, the various elements are not represented to scale so as to favor the clarity of the figures to facilitate understanding.

Furthermore, the different modes or examples and variants are not mutually exclusive and can, on the contrary, be combined with one another.

The invention essentially relates to a process for the manufacture of a conversion crystal 30 by the liquid route, which will be described in detail below.

The fields of application targeted by this manufacturing process are in particular the processes for obtaining X-ray or gamma-ray detectors for medical radiography, the processes for manufacturing non-destructive testing sensors, sensors dedicated to systems, processes for manufacturing sensors dedicated to the nuclear field, or even 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 limiting. For example, obtaining photoelectric crystals used in the constitution of scintillators adapted to the conversion of X or gamma photons into visible photons can be envisaged. The same goes for 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 with longer wavelengths. at 800nm. Finally, the invention can find an application in X-ray imaging for all radiography modalities, whatever the format, for example fluoroscopy, mammography, dental imaging or CT scan.

In particular, the invention can be used in modalities for which it is important to have a strong signal for a minimum dose administered to the patient such as in the case of cardiac imaging, a strong image frequency such as surgical imaging and 3D or high spatial resolution such as mammography or dental imaging. Some applications also concern those where the energy of each X photon is measured, in particular dual energy (bone densitometry, angiography, security application such as baggage checks in airports).

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. The crystals making up the conversion layer can also, depending on the application and their physical nature, 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.

The term crystal is equivalent to the terms “crystalline layer” and represents a monocrystalline or polycrystalline layer. A monocrystalline layer is thus made up of a single grain with a single crystalline orientation. A polycrystalline layer is made up of an assembly of grains of different crystalline orientations.

By "liquid route", it is meant that the conversion crystal is obtained from at least one element dissolved in at least one solvent, the whole being in a liquid form called "liquid precursor" in the following. By varying parameters such as the temperature of the liquid precursor, it is possible to promote the growth of the conversion crystal.

The conversion crystal to be manufactured can be a hybrid perovskite combining an organic part and an inorganic part such as CH ₃ NH ₃ PbBr ₃ . It can also be a completely inorganic perovskite with the general chemical formula ABX3, or mixed compositions such as A ⁽¹⁾ _{1-(y2+…+yn)} A ⁽²⁾ _y2 …A ⁽ⁿ⁾ _yn B ^{(1 )} _{1-(z2+…+zm)} B ⁽²⁾ _z2 …B ^(m) _zm X ⁽¹⁾ _{3-(x2+…+xp)} X ⁽²⁾ _x2 …X ^(p) _xp respecting the electronic neutrality rule, with A and B cations, X an anion and n, m, p integers. Some examples of compositions are given below: MAPbI ₃ , MAPbCl ₃ , MAPbI _3-x Br _x , MA _y GA _1-y PbI ₃ , FAPbBr ₃ , CsPbBr ₃ , Cs ₂ AgBiBr ₆ , CsFAPbI ₃ , Cs _y FA _{1 -y} PbI _3-x Br _x , Cs _1-yz MA _y FA _z PbI _3-x Br _x . MA corresponds to methylammonium [CH ₃ NH ₃ ] ⁺ . FA corresponds to formamidinium [HC(NH ₂ ) ₂ ] ⁺ and GA corresponds to guanidinium [C(NH ₂ ) ₃ ] ⁺ . The conversion crystal to be manufactured, the formula of which is explained above, can also be doped with ionic or non-ionic, organic or non-organic impurities. The conversion crystal to be manufactured can also be formed according to other compositions similar to perovskites known under the following names according to the Anglo-Saxon terminologies: "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 materials of the Ruddlesden−Popper, Dion-Jacobson, Chalcogenide or even Rudorffites types.

The solvent used can be a mixture of solvents. The solvent is preferably of the polar and aprotic type. It can be for example N,N dimethylformamide, Dimethyl sulfoxide, gamma-Butyrolactone, acetonitrile, N-methyl-2-pyrrolidone. It can also be an aqueous solution based on hydrogen halide.

The method of the invention comprises a first step a) consisting in providing a seed crystal 20 whose nature, that is to say the composition and the crystalline phase, allows the growth of the conversion crystal 30 to be manufactured. The seed crystal 20 can be a crystal of the same composition and crystalline phase (homoepitaxy) as those of the conversion crystal 30. The seed crystal can also be of a different nature from that of the conversion crystal to be grown (heteroepitaxy). In the case of the variant of growth from several germs, these germs can be of identical or different natures.

In one example, seed crystal 20 is massive. This advantageously allows it to be reusable or recyclable several times.

The thickness of the seed crystal 20 must be greater than the thickness of the conversion crystal 30 to be manufactured.

In one example, the seed crystal 20 is formed by an assembly of several small seed crystals 20 for a seed crystal 20 of the desired dimensions. This configuration has the advantage of being technically easier to obtain because it is easier to obtain small seeds of well-calibrated size and quality than long, highly elongated seeds. It is thus possible to obtain a row of seeds pressed against each other, all the faces and edges of which are masked with the exception of 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.

In the case where the starting seed, that is to say the seed crystal 20, is a monocrystalline block, the layer which will grow is also monocrystalline (that is to say without grain boundaries). On the other hand, if we start from an assembly of several small seed crystals 20, the layer that will be grown will be polycrystalline and will present grain boundaries, in particular at the joint front of the different small seed crystals 20 .

The method also comprises a step b) consisting in forming a growth mask 12 on the seed crystal 20.

The growth mask 12 is configured to prevent the growth of the conversion crystal 30 to be fabricated where the growth mask 12 is formed on the seed crystal 20. The growth mask 12 is formed so as to cover an edge upper edge 20b of the seed crystal 20. As illustrated in FIGS. 1, 2, 4 and 6, this upper edge 20b is arranged distally with respect to the support face 11a of the substrate 11 on which the seed crystal 20 is positioned in step c).

The part of the growth mask covering the upper edge 20b corresponds to the masking of at least one zone having a height of at least 10 micrometers counted from the upper edge 20b in the direction of the substrate 11, this height preferably being of at least 100 micrometers and ideally of the order of a few hundred microns.

In the rest of the text, the term “edge” means an acute or angular portion of the seed crystal 20 or even areas comprising changes of planes or else an angle area between two faces of crystalline orientations. different.

As illustrated in Figures 1, 2, 4, and 6, growth mask 12 also covers a portion of seed crystal 20 except for at least one growth opening 12a delineated in growth mask 12. In other words, all of the faces of the seed crystal 20 not having to undergo growth recovery must not be in contact with the liquid precursor.

The material making up the growth mask 12 is, during the growth of the conversion crystal, brought into contact with a growth solution otherwise called liquid precursor 40. It must therefore be resistant to this liquid precursor 40 under the conditions of temperature and pressure used. The growth mask 12 can be formed using organic, inorganic materials or a mixture of the two, such as parylene or parylene C, a photolithography resin such as an orthogonal resin, BCB or SU8, silicone, a thermally crosslinkable material or to ultraviolet rays such as epoxy or acrylate compounds, a fluorinated solvent (CYTOP©), a layer of Al ₂ O ₃ , SiO ₂ or even a metal layer (Cr, Cu, Pt). The growth mask 12 can be produced in one layer, or several layers superimposed or deposited one beside the other so as to cover the seed crystal 20 while avoiding any visible zone outside of said growth opening 12a.

The deposition can be done by liquid means, such as for example with methods of sprinkling, dipping, by "slot-die", by inkjet, by 3D printing or by brush deposition, by vacuum techniques such as evaporation, sputtering, 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 seed crystal 20 in order to avoid initiating parasitic growths from the seed crystal 20. growth opening 12a is either present from the deposition of the growth mask 12, or obtained after the 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 zone during the deposition of the growth mask 12, either by so-called subtractive techniques such as laser ablation, photolithography, etching, or the lift-off technique well known to those skilled in the art.

If the seed crystal 20 were not masked, the growth of the conversion crystal would take place in all directions of space except for the face on which the seed is stuck. In particular, the conversion crystal in formation would also grow in the direction perpendicular to the plane of the substrate 11, which would not make it possible to precisely control both the thickness of the conversion crystal and the surface of the substrate to be covered.

In one example, the growth mask 12 can also have the function of a glue in order to mechanically maintain the seed crystal 20 on the substrate 11.

In an example shown on the , one face of the seed crystal 20 in contact with the substrate 11 is not covered by the growth mask 12. This configuration must nevertheless make it possible to ensure that the liquid precursor 40 does not penetrate between the seed crystal 20. Thus , parasitic growth cannot occur.

As illustrated in FIGS. 1, 2, 4 and 6, the manufacturing method further comprises a step c) which consists in positioning the seed crystal 20 on the support face 11a of the substrate 11. This positioning is entirely constrained by two imperatives .

First, the seed 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 face of stable growth orientation, is parallel to the support face 11a . For the implementation of this condition, the seed crystal may present, on its outer face oriented away from the support face 11a, an orientation different from the orientation of the crystalline plane 20d corresponding to an orientation face of steady growth; the positioning of the germination crystal 20 will all the same make it possible to achieve the object of the invention as long as the orientation of the crystalline plane 20d corresponding to the stable growth orientation face is parallel to the support face 11a. In other words, the crystal plane 20d corresponding to the stable growth orientation face can be arranged inside the seed crystal 20, regardless of the orientation of the apparent outer face of the seed crystal 20. In particular , it does not matter whether the exposed outer face has defects or is cut.

In other words, the face of stable growth orientation is a face in which run several chains of periodic bonds. The corresponding crystalline planes are necessarily crystalline planes which are generally dense planes therefore with low Miller indices h,k,l < 3.

An equivalent way to implement this first condition is to position the crystalline plane 20d corresponding to a stable growth orientation face on the side of the support face 11a and parallel to the support face 11a. Thus, even if the seed crystal has, on its outer face arranged towards the support face 11a, an orientation different from the orientation of the crystalline plane 20d corresponding to the stable growth orientation face; the positioning of the germination crystal 20 will make it possible to achieve the object of the invention as long as the orientation of the crystalline plane 20d corresponding to the stable growth orientation face is parallel to the support face 11a.

Then, the positioning of the seed 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, with the substrate 11, an angle as close as possible to 90°. In one example, a crystal with a cubic crystallographic structure can achieve this angle.

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

In one example, in step c), the orientation of the seed crystal 20 is carried out precisely, typically to within 1°, or even preferentially to within 0.1° or 0.01°. The crystallographic orientation of the seed crystal 20 can be easily controlled, even when the outer face of the seed crystal 20 has a different orientation from the orientation of the crystal plane 20d corresponding to the stable growth orientation face, by carrying out characterizations under X-ray diffraction, of the Laue, θ/2θ type, or else of the “rocking curve” type according to the established Anglo-Saxon terminology. Mechanical parts can also be used to set the orientation of the seed crystal 20 relative to the surface of the substrate 11.

In a particular case of the invention, the orientation of the seed crystal is different from 90°. This makes it possible to grow the conversion crystal by inducing a continuous, increasing or decreasing thickness gradient, as the conversion crystal advances on the surface and during growth.

In a further example, seed crystal 20 and conversion crystal 30 to be fabricated have a cubic crystal system.

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

In this example, if the growth face is of crystallographic orientation (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 is of crystallographic orientation (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 advisable to choose, among all the possible stable faces, a face of growth of Miller indices (hkl) and a perpendicular face of different Miller indices (abc). In this example, the structure being cubic, any pair of stable faces whose indices satisfy the relation h.a+k.b+l.c=0 can be selected.

However, all crystal orientation couples giving rise to stable crystal faces, so that a first crystal plane 20d of the seed crystal 20 is parallel to the support face 11a and so that at least one growth face 20a of the seed crystal 20 is arranged transversely to the support face of the substrate 11, are possible within the scope of this invention.

In an example of implementation of the manufacturing process, the seed crystal 20 is composed of several seeds assembled together.

The seed crystal 11 can be fabricated in a single block by conventional self-supported monocrystal growth techniques. Its surface may optionally be treated mechanically, for example by polishing and/or cutting adapted to the correct dimensions and/or chemically. It is also possible to use a solvent to adjust the surface state of the seed crystal and/or to use one or more physical treatment(s), for example plasma or laser on each starting face. of growth of the germ, so as to voluntarily generate defects which will favor the resumption of growth.

In a particular case of the invention, the seed crystal 20 can grow directly from the surface of the substrate.

As illustrated in FIGS. 2, 3 and 6, the method according to the invention also comprises a step d) which consists in applying the liquid precursor 40 of the conversion crystal 30, from the support face 11a of the substrate 11 up to at least 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 thickness of growth 30b contained between the face support 11a of the substrate 11 and an upper edge 12b of the growth opening 12a arranged distally with respect to the support face 11a of the substrate 11. The term "distal" equivalently means that the upper edge 12b is arranged the opposite of the substrate 11. The upper edge 12b can have any shape induced by the way of masking the crystal. In one example, the upper edge 12b is serrated or in the form of slots in order to obtain a suitable topology of the upper surface of the crystal in formation. However, the cutting of the upper edge 12b should be such that it allows the growth of stable faces. In the example of a slotted cut, the vertical parts of the slots must correspond to stable faces just like the part of the slots being horizontal.

Growth thickness 30b may be slightly larger than growth opening 12a. Indeed, in the case where the growth mask 12 covers the lower edge 20c of the seed crystal 20, the growth disturbances induced in this zone close to the substrate induce that the seed crystal tends to grow until reaching the substrate 11. Nevertheless, the upper facet of the conversion crystal being formed remains flat.

In the rest of the text, “free growth” means growth without mechanical constraint. Thus, free growth is different from growth of a crystal or a polycrystal constrained between two walls and mechanically leaving only one growth direction or two opposite growth directions possible. This is advantageous for obtaining a very flat and uniform surface state, corresponding to stable crystalline faces.

In the rest of the text, the term “growth” corresponds to a formation, a homoepitaxy, a heteroepitaxy or even a crystallization.

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

The substrate 11 can be passive by being a simple support or can be active, that is to say have an additional functionality. In particular, the substrate 11 can comprise an active matrix, for example with transistors, or a passive matrix, as with discrete pixels without transistors. In the case where the matrix is active, it is possible to use many existing technologies of known transistors (a-Si, IGZO, organic transistors, polysilicon). It is also possible to use so-called CMOS technologies to integrate many transistors within the same pixel and perform signal processing at the pixel level. The use of CMOS is particularly advantageous in the case of applications in X and gamma spectrometry. The substrate 11 can for example be made of glass, of plastic such as polyimide, PET, PEN, or else based on silicon.

The surface of the substrate 11 can be prepared beforehand so as to guarantee correct adhesion of the conversion crystal 30 to the substrate 11. Similarly, the substrate 11 can be prepared so as to guarantee contact on the molecular scale between the crystal of conversion and the support face 11a. For example, the perovskite conversion crystal may have a strong chemical affinity with the support face 11a representing a surface of a conductive electrode of an optoelectronic device so as to facilitate the transfer of charge from one to the other. The adhesion of the conversion crystal 30 to the substrate 11 is ensured by covalent bonds, ionic or Van Der Waals bonds between the conversion crystal 30 and all or part of the surface of the substrate 11, or by the roughness and the its topology. In particular, the lateral growth mode obtained via the manufacturing process described in this document allows the growth front to grow gradually and in intimate contact with the surface of the substrate 11, which promotes adhesion on this surface.

In one example, the adhesion of the conversion crystal 30 to the surface of the substrate 11 is ensured mechanically via the topology and the roughness of the surface, or chemically via the presence of chemical groups adapted to the surface by known self-assembled monolayers 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.

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

In general, at least one growth opening 12a is arranged at the level of the growth face 20a so that only a flat and smooth portion of the growth face 20a is capable of being in contact with the liquid precursor 40 of the crystal of conversion 30.

All the geometries of the growth opening 12a can be envisaged, such as for example square or rectangular in shape. It should nevertheless be ensured that the seed crystal 20 is large enough to cover the entire area of interest of the substrate.

In the rest of the 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 face portion present in the morphology of crystal 30 under the growth conditions used (solvent, temperature).

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

When the liquid precursor 40 is in the undersaturated state, the solute concentration of the conversion crystal 30 is lower than the solubility limit of the solute of the conversion crystal in the liquid precursor 40. This state makes it possible to slightly dissolve the face growth of seed crystal 20 at growth opening 12a. Thus, surface defects (chips, stresses, pollution) are dissolved before carrying out a subsequent growth phase.

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 of 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 face of Growth at growth opening 12a is spontaneous.

The state of under-saturation or over-saturation is generally controlled by the temperature, the conversion crystal concentration 30, the nature of the solvent, the use of a non-solvent or even the pressure. The conditions allowing the growth are conventional and known to those skilled in the art. In the case of using temperature as a parameter, it is possible to implement crystallization by increasing temperature in the case of retrograde solubility, or by decreasing temperature in the case of direct solubility, or by setting constant temperature and concentration conditions to maintain an adequate level of supersaturation.

The conditions allowing the growth are known to those skilled in the art, for example by varying the temperature of the solution as illustrated in the or by the use of a non-solvent. Oriented growth relies on controlling the supersaturation applied so that only screw dislocation growth is active, corresponding to a spiral mode of growth. Thus, only the screw dislocations originating from the growth face 20a, at the level of the growth opening 12a, are active and allow growth. In order to carry out the growth exclusively by screw dislocation, it is necessary on the one hand to ensure a sufficient level of purity to avoid the blocking of the growth by impurities with lower supersaturation and on the other hand to limit the supersaturation to avoid the growth by 2D nucleation.

An example of conditions suitable for the manufacturing process of the invention is given below. A single crystal seed crystal having flat, smooth faces that do not depolarize light is selected. This seed crystal 20 is bonded to a silicon substrate with a silicone glue. The substrate is glued to the bottom of a glass reactor, with this same silicone glue. The seed crystal 20 is covered with the growth mask 12 except at the level of a growth opening 12a. A liquid precursor 40 of MAPbBr ₃ at 1 mol/L is obtained by dissolving the PbBr ₂ and MABr precursors in a 1:1 ratio at room temperature and in N,N-Dimethylformamide. The seed crystal 20 and the liquid precursor 40 are temperature adjusted separately for a period of 1 hour at a temperature of 55°C. The liquid precursor 40 thus heated is then poured onto the seed 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. and by following the temperature profile presented on the . The liquid precursor 40 is for example stirred using a propeller or even renewed and set in motion by a device described on the .

In the example shown in the , the liquid precursor 40 can be obtained by dissolving a nourishing body, formed for example of an excess 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 seed crystal 20. The liquid precursor 40 is sucked up by a pumping system 71, then filtered by a filtration system 72 before supplying the reactor. Then, the liquid precursor 40 is again put into circulation towards the accumulator 70, and so on, according to a closed circuit organization. The retentate 73 which is retained by the filtration system 72 is reintroduced into the accumulator 70. Coupled with the manufacturing process described above, these arrangements make it possible to obtain that all of the nourishing body dissolved in the accumulator 70 is deposited on the substrate 11 in the form of the conversion crystal 30, which implies a gain for the manufacturing cost.

It is advantageous to ensure effective renewal of the solution in contact with the conversion crystal 30. Indeed, this limits the boundary layer phenomena which lead, for large dimensions, to growth instabilities, by setting in a walking bunch or wobbling of steps, conducive to the formation of structural defects harmful 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 contact and / or chemical between the conversion crystal 30 and the surface of the substrate 11.

In one example, during step d), the growing conversion crystal 30 comprises an upper planar facet 30a parallel to the support face 11a and whose dislocations are non-active.

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

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

Thus, thanks to the manufacturing process described in this document, the conversion crystal 30 comprises from the start and during its growth an upper facet 30a naturally planar, parallel to the support face and without active dislocation, that is to say whose dislocations are only non-active dislocations. This makes it possible to control the thickness of the conversion crystal 30 obtained by maintaining it at the height of the upper edge 20b of the growth opening 12a. Indeed, non-active dislocations do not allow growth to resume and the thickness of the crystal, during its growth, therefore does not increase. This is advantageous for very precisely controlling the thickness of the conversion crystal 30 obtained and therefore ultimately the quantity of radiation absorbed by the conversion crystal 30 when it is installed in an optoelectronic device.

The conversion crystal 30 obtained via the manufacturing process described above contains defects of the screw dislocation type whose line is parallel to the direction of growth, in a plane parallel to the substrate 11. These dislocations will be perpendicular to the direction of drainage of the charges 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 the perovskites, the configuration thus obtained is very favorable for avoiding the phenomena of ionic migration in the thickness of the conversion crystal 30, and thus limit electrical instabilities.

The thickness of the conversion crystal 30 is mainly controlled by the size of the growth opening 12a. The conversion crystal 30, once formed, preferably has a thickness greater than 1 micrometer, preferably greater than 100 micrometer and even more preferably greater than 300 micrometer. In the case of direct conversion X-ray detectors, the thickness of the conversion crystal 30 to be manufactured is defined so as to absorb the greater part of the incident radiation at the energy targeted for the application. For example, to absorb X-rays equivalently to 600 micrometers of CsI, which is today the most widely used converter material in medical radiography, (85% X-ray absorption at RQA5 and 50% at RQA9), it is appropriate to form a conversion crystal 30 having a thickness of 600 micrometers in CH ₃ NH ₃ PbI ₃ or of 1300 micrometers in CH ₃ NH ₃ PbBr ₃ at RQA 5 (X-ray spectrum centered on 50keV according to standard IEC62220 -1), or a thickness of 450 micrometers in CH ₃ NH ₃ PbI ₃ , or 800 micrometers in CH ₃ NH ₃ PbBr ₃ at RQA9 (X-ray spectrum centered on 70keV according to standard IEC62220-1).

In an example shown on the , the method comprises the additional step d0) which consists in configuring the liquid precursor 40 of the conversion crystal 30 so that it is in a state of under-saturation 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 allows the growth face of the seed crystal 20 to be slightly dissolved at the level of the growth opening 12a. Thus, a defect-free surface is advantageously obtained before carrying out a subsequent growth phase according to step d).

According to an example of the manufacturing method, in step b), the growth mask 12 is also formed so as to cover a lower edge 20c of the seed crystal 20 arranged proximally with respect to the support face 11a of the substrate 11. These arrangements are advantageous because, otherwise, the growth of the conversion crystal is disturbed and can lead to a polycrystal instead of the expected single crystal.

In one example, the length of the seed crystal 20 is greater than or equal to the lateral dimension of the zone of the substrate 11 to be covered. However, as shown in the , the case can also be envisaged where the length of the seed crystal 20 is smaller than the lateral dimension of the zone of the substrate 11 to be covered. In this case, it is possible to mask only certain areas of the seed crystal 20 to ensure that the conversion crystal 30 ends up covering the appropriate surface of the substrate 11.

In an example of the method, the upper edge 12b of the growth opening 12a is parallel to the support face 11a of the substrate 11. This configuration makes it possible to control the flatness of the conversion crystal 30 and therefore the homogeneity of the conversion yield. of radiation.

In an example shown on the , during step b), an additional growth opening 12a is arranged on a face of the seed crystal 20 opposite to the growth face 20a. It goes without saying that, therefore, the face of the seed 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 cause the crystal to grow in several directions with respect to the starting seed.

According to an example of the manufacturing method, during step b), the growth mask 12 is formed by an adhesive 60. The adhesive may be inert with respect to the seed crystal 20. As illustrated in there , the adhesive 60 can overflow from the seed crystal 20 so as to completely cover the face of the seed crystal 20 arranged opposite the support face 11a of the substrate 11.

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

In an example of the method, during step c), the positioning of the seed crystal 20 is carried out so that the seed crystal 20 is offset with respect to a zone 50 of the substrate 11 where the conversion crystal 30 to be manufactured is form. This is advantageous for homogeneously covering a determined zone of the substrate 11.

In an example shown on the , the manufacturing method comprises a step f) implemented after step d). Step f) consists in treating the conversion crystal 30 so as to make the seed crystal 20 and the conversion crystal 30 independent after the formation of the crystal 30. Thus, at the end of growth, the seed crystal 20 can be left on the surface and/or be removed from the surface by mechanical or physical cutting (laser) and/or by peeling it off from the surface of the substrate 11.

In an example shown on the , the method comprises step e) which is implemented after step d). Step e) consists in treating the conversion crystal 30 so as to make at least one of its faces rectilinear.

In an additional implementation of the invention, masking step b) can be reproduced several times. In other words, once step b) has been carried out for the first time, steps c) and d) are implemented to obtain a first part of the conversion crystal 30. The growth is then stopped. The conversion crystal 30 thus obtained is then used as seed crystal 20 in a new iteration of step a). The conversion crystal 30 is then masked in a new step b) then the rest of the process is carried out again. It may thus be envisaged to repeat the process several times. This technique makes it possible to avoid the fact that over too long growth times, defects are generated on the upper facet 30a and that these defects induce growth in the direction normal with respect to the substrate 11 and the support face 11a. In this implementation, the growth is stopped before these defects are formed, a new masking is formed and the growth is then restarted following steps c) and d). This approach involves the masking being removed from the top facet 30a at the end of the process.

Thus, once the conversion crystal 30 has been obtained, its surface can be mechanically or mechanically chemically treated, for example by mechanical-chemical polishing, and/or chemically, for example by solvent cleaning, chemical grafting to modify the surface state and /or physically by UV-O ₃ or plasma treatment. It is for example possible to re-polish the upper face of the crystal 30 to guarantee better uniformity 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 side dimensions.

An optoelectronic device, not shown, can be manufactured from the conversion crystal 30 obtained with the manufacturing method described above. In order to manufacture 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 an example, a single upper electrode is common to all the pixels of the matrix. This electrode can have the same nature as the lower electrode constituting the part of the substrate 11 on which the conversion crystal 30 is obtained or be of a different nature, as for 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 overlay of these materials. It is also possible to use one or more interface layers on the electrode to fix the work function and the chemical compatibility with the perovskite (PEIE, C60, MoO ₃ , V ₂ O ₅ , BCP, SPIRO). The upper electrode is then electrically connected to the external circuit, for example by means of a conductive wire or a conductive line produced by printing.

The conversion crystal 30 can finally be encapsulated in air, or in an inert atmosphere (N ₂ , Ar), or in an anhydrous atmosphere. This can be achieved using a glass cover glued to a surface of the substrate 11, which is not covered by the conversion crystal 30, using a bead of glue, or using an adhesive such as a glue or a pressure-sensitive adhesive and a plastic film with barrier layers. The encapsulation is transparent or opaque to visible light, but allows the radiation to be detected to pass.

The contact pads of the pixel matrix are then connected to a reading electronics using flexible hoses and glues of the ACF (Anisostropic Conductive Film) type. The matrix can be characterized with the usual reading methods of pixelated imagers.

Claims (18)

Process for the oriented manufacture of a conversion crystal (30) by a liquid process, the process comprising the following steps:
a) providing a seed crystal (20) allowing the growth of the conversion crystal (30) to be manufactured;
b) forming a growth mask (12) on the seed crystal (20), the growth mask (12) being configured to prevent the growth of the conversion crystal (30) to be fabricated at the location where the growth mask (12) is formed on the seed crystal (20), the growth mask (12) being formed so as to cover on the one hand an upper edge (20b) of the seed crystal (20) arranged distally with respect to to a support face (11a) of a substrate (11) on which the seed crystal (20) is positioned in step c), on the other hand on a part of the seed crystal (20) with the exception at least one growth opening (12a) delimited in the growth mask (12);
c) positioning the seed crystal (20) on the support face (11a) of the substrate (11) so that the seed crystal (20) is oriented so that a first crystalline plane (20d), corresponding to a face d stable growth orientation of the seed crystal (20), is parallel to the support face (11a) and so that at least one growth face (20a) of the seed 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 capable of being in contact with a liquid precursor (40) of the conversion crystal (30);
d) applying the liquid precursor (40) of the conversion crystal (30) configured in a state of relative supersaturation at least at 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), along a growth thickness (30b) contained between the support face (11a) of the substrate (11) and an upper edge (12b) of the growth opening (12a) arranged distally relative to the support face (11a) of the substrate (11). A method of making a conversion crystal (30) according to claim 1, wherein the method includes the following additional step:
d0) configuring the liquid precursor (40) of the conversion crystal (30) so that it is in a state of under-saturation at least at the level of the flat and smooth portion of the growth face (20a), the step d0) being carried out before step d). A method of making a conversion crystal (30) according to any of claims 1 or 2, wherein in step d) the growing conversion crystal (30) includes an upper facet (30a ) flat, parallel to the support face (11a), and whose dislocations are non-active. A method of manufacturing a conversion crystal (30) according to any one of claims 1 to 3, wherein during step c) the orientation of the seed crystal (20) is carried out at least 0.1° near. A method of making a conversion crystal (30) according to any of claims 1 to 4, wherein in step b) the growth mask (12) is formed to cover an edge bottom (20c) of the seed crystal (20) arranged proximally relative to the support face (11a) of the substrate (11). Method of manufacturing a conversion crystal (30) according to any one of claims 1 to 5, in which the upper edge (12b) of the growth opening (12a) is parallel to the support face (11a) of the substrate (11). Method of manufacturing a conversion crystal (30) according to any one of Claims 1 to 6, in which, during step b), at least one additional growth opening (12a) is arranged on at least an additional growth face (20a) of the seed crystal (20) arranged transversely to the support face of the substrate (11). A method of manufacturing a conversion crystal (30) according to any one of claims 1 to 7, wherein the seed crystal (20) and the conversion crystal (30) to be manufactured have a cubic atomic structure. Method of manufacturing a conversion crystal (30) according to any one of claims 1 to 8, in which the conversion crystal (30) to be manufactured is an ABX ₃ type perovskite, A' ₂ C ¹⁺ D ^{3 +} X ₆ , A ₂ B ⁴⁺ X ₆ or A ₃ B ₂ ³⁺ X ₉ 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. A method of 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 ⁽¹⁾ _{1-( y2+…+yn)} A ⁽²⁾ _y2 …A ⁽ⁿ⁾ _yn B ⁽¹⁾ _{1-(z2+…+zm)} B ⁽²⁾ _z2 …B ^(m) _zm X ⁽¹⁾ _{3-(x2+…+xp )} X ⁽²⁾ _x2 …X ^(p) _xp , respecting the rule of electron neutrality, with A ⁽ⁿ⁾ and B ⁽ⁿ⁾ cations, X ⁽ⁿ⁾ an anion and n, m, p integers. A method of making 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}. Method of manufacturing a conversion crystal (30) according to any one of claims 1 to 11, in which, during step b), the growth mask (12) is formed by an adhesive (60) . Method of manufacturing a conversion crystal (30) according to any one of claims 1 to 12, comprising the following step, implemented after step d):
e) treating the conversion crystal (30) so as to make straight at least one of the faces of the conversion crystal (30). Method of manufacturing a conversion crystal (30) according to any one of claims 1 to 13, in which the seed crystal (20) is composed of several seeds assembled together. A method of manufacturing a conversion crystal (30) according to any one of claims 1 to 14, wherein during step d) a temperature of the liquid precursor (40) of the conversion crystal (30) is changed gradually over time. A method of manufacturing a conversion crystal (30) according to any one of claims 1 to 15, wherein, during step c), the positioning of the seed crystal (20) is carried out such that the crystal of nucleation (20) is offset with respect to an area (50) of the substrate (11) where the conversion crystal (30) to be manufactured is formed. A method of manufacturing a conversion crystal (30) according to any one of claims 1 to 16, comprising the following step implemented after step d):
f) treating the conversion crystal (30) so as to make the seed crystal (20) and the conversion crystal (30) independent of each other. Optoelectronic device comprising a conversion crystal obtained by growth in the optoelectronic device and according to one of Claims 1 to 17, in which the conversion crystal has a thickness greater than or equal to 100 micrometers.