FR2605166A1 - Solid-state photosensitive device, method of reading and method of manufacture - Google Patents

Abstract

The present invention relates to a solid-state photosensitive device. It also relates to a method of reading and a method of manufacturing this device. It refers to a matrix photosensitive device organised as a so-called "x-y" structure, each photosensitive element of which consists of two photodiodes d, D, mounted head-to-tail. One of the photodiodes d has a capacitance at least substantially ten times smaller than that of the other photodiode D. The low-capacitance photodiode d is connected to a row 11, 12, 13 of the matrix and operates as a switch which is closed only when addressing this row by addressing means 5.

Description

SOLID PHOTOSENSITIVE DEVICE,
READING METHOD AND MANUFACTURING METHOD
The present invention relates to a photosensitive device in the solid state. It also relates to a reading method and a method of manufacturing such a device.

 Numerous matrix photosensitive devices are known in the prior art organized according to a so-called "xy" structure, that is to say that they comprise a network of rows and columns and that at the intersection of each row and each column there is a photosensitive element connected to this line and to this column.

The electronic addressing of each line triggers the passage of the information contained by the photosensitive elements of this line on the columns to which these photosensitive elements are linked. At the end of the columns, there are reading devices, such as amplifiers or charge transfer registers which collect the information and multiplex it.

 The present invention provides a photosensitive device in the solid state, which can be matrix or linear, and which in particular has the following advantages - the capacities of the columns are very low, which simplifies the production of the reading devices located at the end of the columns , - the photosensitive elements of the unaddressed lines are very well decoupled from the columns which minimizes the problems of leakage currents, crosstalk, "smearing" ...

By the article entitled "Amorphous silicon linear image sensors" published by Hitachi, in the journal "Amorphous Semiconductor
Technologies ans Devices "in 1984, a bar was known whose photosensitive elements consist of two identical photodiodes, mounted in series and head to tail.

 Compared to Hitachi's article, our invention which proposes photosensitive elements constituted by two elements of very different capacities makes it possible to significantly lower the value of the capacities of the columns and also to improve the decoupling compared to the columns of the photosensitive elements unaddressed lines. In addition, in the Hitachi article, one of the photodiodes of each photosensitive element is made insensitive to light radiation, which complicates the production and is not the case in our invention.

 The present invention relates to a photosensitive device in the solid state comprising - a network of horizontal connections or lines and at least one vertical connection or column crossing the lines; - a photosensitive element connecting each line and each column which intersect; - Means ensuring the sequential addressing of each line # of photosensitive elements for reading; - a circuit ensuring the reading and the multiplexing of the columns; device characterized in that each photosensitive element consists of first and second elements mounted in series, the first so-called low-capacity element having a capacity at least substantially ten times lower than that of the second so-called high capacity element, in that that at least each element of high capacity is photosensitive, the photosensitivity of an element resulting in a leakage current of this element and in that each element of low capacity is connected to a line, and functions as a switch, closed only when addressing the line by the addressing means.

 The present invention also relates to various methods of reading and manufacturing the photosensitive device according to the invention.

Other objects, characteristics and results of the invention will emerge from the following description, given by way of nonlimiting example and illustrated by the appended figures which represent:
- Figure 1, the diagram of an embodiment of a matrix photosensitive device according to the invention;
- Figures 2a, b, c, 3a, b, c, d, e, diagrams explaining the operation of the device of Figure 1;
- Figures 4a, b, c, 8a, b, c, 9a, b, c, d diagrams illustrating various methods of reading the photosensitive device according to the invention
- Figures 5, 6, 7, diagrams of three embodiments of the photosensitive elements;
- Figure 10, the diagram of an embodiment of the addressing means ;;
- Figures 12a, b, 13, 14a, b, and 15a, b, diagrams illustrating various methods of manufacturing the device according to the invention.

 In the different figures, the same references designate the same elements, but, for reasons of clarity, the dimensions and proportions of the various elements are not observed.

 FIG. 1 schematically represents a photosensitive device in the solid state of the matrix type.

 This device comprises a network of horizontal connections or lines 11, 12, 13 and a network of vertical connections or columns c1, c2, C3. To simplify the diagram, FIG. 1 shows only three rows and three columns.

 A photosensitive element connects each row and each column that intersect. In the embodiment of FIG. 1, each photosensitive element consists of two photodiodes d and D, in series, and head to tail. The anode of photodiode d is connected to a line and the anode of photodiode D is connected to a column. Photodiodes d and D have very different capacities. The capacity of the photodiode d is at least substantially ten times lower than that of the photodiode D. For reasons of practical realization, photodiodes d and D of very different capacities are obtained by playing on the respective surfaces of the diodes d and D whose other parameters are identical or similar.

 It is possible to obtain photodiodes of very different capacities by playing on other parameters than. the surface such as thickness, doping, materials with different dielectric constants, or by playing on several parameters simultaneously.

 The columns are brought to a fixed voltage, equal for example to ground, in the embodiment of FIG. 1 where the circuit 2 ensuring the reading and the multiplexing of the columns is constituted by transimpedance amplifiers.

 Each column is connected to the negative input of an operational amplifier 3, the positive input of which is grounded. The outputs of the amplifiers are connected to a multiplexer 4 which supplies the output signal S of the matrix. The amplifiers' outputs are also looped back to their negative input via a resistor R.

 When the circuit ensuring the reading and the multiplexing of the columns is constituted by a charge transfer device, the columns are not brought to a fixed voltage but the voltage fluctuations are however negligible compared to the voltage variations on the lines and on the photosensitive elements.

 In addition to its function of polarizing the columns at a substantially constant voltage, the circuit 2 must read the current or the charge flowing on the columns and multiplex this information.

 A logic shift register 5 ensures the sequential addressing of each line of photosensitive elements for reading.

Each output of the register is connected to a line of the matrix. This register 3 carries a voltage pulse Seen from line to line, while the other lines are grounded.

 We will now describe the operation of the photosensitive device of FIG. 1 by focusing in particular on the operation of, the photosensitive element connected to the column c2 and to the line 12. We call A the point common to the photodiodes d and D.

 In FIGS. 2a, b and c, there is shown, as a function of time t, the voltage V12 applied to line 12 by the shift register 5, the voltage VA at point A of the photosensitive element connected to line 12 and to column c2 and then the contribution i from line 12 to the current from column c2.

 At time t1, a voltage pulse of amplitude VO arrives on line 12 and remains there until time t2 when the voltage on line 12 becomes zero again.

 At the end of a tri time, the voltage on line 12 becomes equal to VO again and remains there from a new instant tl to a new instant t2.

 The arrival of the pulse VO at time tl on line 12 polarizes the photodiode d directly and the photodiode D in reverse. Point A is polarized at VOS at the bend voltage of the photodiode d close.

 In FIG. 3a, the photodiodes d and D are shown in series connected between line 12 and column c2. FIG. 3b shows that at time tl, the photodiode D is in reverse and represented by a capacitor of capacity equal to CD, connected to ground while the photodiode d is direct and represented by a capacitor of capacity equal to Cd, short-circuited by a switch i, and connected to a voltage VO.

 On the frames of the CD capacity, there is an amount of charge equal in absolute value to CD. VO.

et est donc très faible puisque Cd < < CD. En conséquence, le potentiel sur A reste peu éloigné de VO et la photodiode d se trouve polarisée en inverse. La photodiode D reste polarisée en inverse.At time t2, the potential of line 12 returns to zero, the variation of potential VA at point A equals

and is therefore very low since Cd <<CD. Consequently, the potential on A remains not far from VO and the photodiode d is reverse polarized. Photodiode D remains reverse biased.

qui est illustrée sur la figure 2c. Sur les armatures de la capacité
CD, il y a une quantité de charge égale en valeur absolue à

The reverse polarization of the photodiode d causes the circulation of a quantity of charge Q supplied by the column and
p equal to

which is illustrated in Figure 2c. On capacity frames
CD, there is an amount of charge equal in absolute value to

 From time t2, photodiodes d and D are reverse biased, it is the period of integration of charges ti which begins. Photodiodes d and D therefore behave like capacitors Cd and CD with currents Id and ID. These leakage currents are composed of a current 10 linked to the characteristic l (V) of the diodes in the dark and of a current Iph proportional to the illumination.

et la charge stockée au point A après un temps d'intégration t.Between the instant t2 and the instant t3, which precedes the new instant tl, during the integration period ti, there is summation at point A of the leakage currents coming from the photodiodes d and D, in reverse and head to tail, d 'or

and the charge stored at point A after an integration time t.

equal:

While the QA charge is being stored at the point
A, there is injection of a current Ii on column C2 which equals

 The load - QA is distributed over the two capacities Cd and CD.

The charge stored on photodiode D equals

On the reinforcement of the CD capacity, there is an amount of charge equal in absolute value to, #:

At a new instant tl, the voltage on line 12 again passes to VO. The photodiode d is again directly polarized, which amounts to driving the Cd capacity. The CD capacity is loaded in absolute value at | CDVo | .There is therefore circulation on column c2 of a Qreading charge equal to

This charge contains useful information since

It is read by a transimpedance amplifier which transforms it into voltage, then is multiplexed with the charges delivered by the other photosensitive elements of the same line 12 and the multiplexed signal constitutes the output signal S of the device.

 During the period ti of charge integration in the photosensitive elements of line 12, we will examine what is the current injected into the columns by the photosensitive elements of line 12.

 During the period ti, the photodiodes d and D are in reverse and produce a leakage current ID and Id and a noise current.

The current I. which is injected into the columns due to the leakage current ID and Id of the photodiodes is written

The condition posed on the respective values of the capacities Cd CD, and therefore Cd at least ten times less than
CD, implies that current 1. has a low value and may even be zero.

et le courant I. n'annule. Il faut cependant dans ce cas que les photidiodes d et D reçoivent le même éclairement, quelle que soit sa valeur.In particular, when the photodiodes differ only in their surfaces, the currents Id and ID are proportional to the surfaces of the diodes and therefore to their capacities, which is written:

and the current I. does not cancel. In this case, however, the photidiodes d and D must receive the same illumination, whatever its value.

 The leakage current Ii injected by the photodiodes on the columns may be noisy. The noise currents due to photodiodes D and d are designated by IbD and Ibd respectively. These currents are weak, of the second order.

The noise current Ibi injected into column c2 by the photosensitive element connected to line 12 and to column c2 is written:

In the particular case previously considered where

 Like Cd CD, the noise current injected into column c2 is very low.

 In the other cases, the noise current Ibi is always low, of the second order, and does not cancel either.

 In conclusion, it can therefore be seen that during the period of integration of the charges ti of the line 12, the leakage and noise current from the reverse-biased photodiodes d and D which is injected into the columns is very low. We can therefore use the columns to read the other rows of the matrix, without row 12 causing crosstalk.

 During the integration period ti of line 12, the shift register moves the pulse VO from line to line over the entire matrix and then returns to line 12 so that it can be read. In this type of operation, the light information constantly arrives over the entire matrix, as in the case of a television shooting for example.

 In FIGS. 4a, b, c, there is shown symbolically, the light information i which arrives permanently on the matrix and the voltages V12 and Vlm received by the lines 12 and lm. The arrival of a voltage pulse V causes the photosensitive elements of the line to be read. Two successive readings are separated by an integration period ti. We only read one line at a time and while the other lines are in the integration period.

With regard to the capacity of the columns, the calculation shows that it is very low thanks to the condition imposed on the capacities
CD and CD.

The capacity of a photosensitive element during the integration period is worth:

 The capacity of a photosensitive element that is being read is worth CD.

In the case of a matrix of n rows, the capacity of a column equals:
(n - I). CD + CD
If n is large, the capacity of a column is therefore substantially equal to n. CD.

 As the capacity Cd is chosen to be of low value, the capacity of the columns is therefore low, which simplifies the construction of the circuit for reading the columns.

 In the embodiment of FIG. 1, it has been considered that each photosensitive element comprises two photodiodes d and D.

The photodiode d can be replaced by a diode d ', which can be obtained by making the photodiode d blind. Indeed, what is essential is that the element d or d of low capacity behaves like a switch, which is closed when reading a line and which remains open during the integration of the charges in this line.

It is desirable that the element of low capacity is photosensitive because it increases the information collected since the leakage currents of elements of low and high capacity are added in absolute value. Another advantage of using an element of low photosensitive capacity is that it makes it possible to cancel the leakage current injected into the columns during the integration period, in particular in the case of two photodiodes differing only in their surface and receiving the same illumination.

 The preceding description essentially based on FIG. 1 where each photosensitive element consists of two photodiodes in series and head to tail also applies, more generally in the case where each photosensitive element consists of a first and a second element in series, with the following characteristics: the first so-called low-capacity element has a capacity at least substantially ten times lower than that of the second so-called high-capacity element; - At least the second element is photosensitive and its photosensitivity results in a leakage current; - The first element is connected to a line and functions as a switch, closed only when the line is addressed by the addressing means.

 We will examine in the following various embodiments of the photosensitive elements.

 In Figure 5, there is shown schematically an embodiment of a photosensitive element in which the high-capacity element is constituted by a photo-resistance PR The high-capacity element when it is constituted by a photodiode is permanently in reverse; however, there is little difference between the characteristic of a photodiode in reverse and that of a photoresistor.

 In the embodiment of FIG. 6, the element of low capacity is an optically controlled photodiode d. The photodiode d is connected to a DC voltage source of value Vo and the voltage VO is only transmitted to point A when the photodiode d receives a light pulse.

 It is understood that the two embodiments of FIGS. 5 and 6 can be combined. A photodiode d, optically controlled, in series with a photoresistor is then obtained as an element of low capacity.

 In the embodiment of FIG. 7, the element of low capacity is constituted by a photo-resistance P. R2. This photoresistor is connected to a DC voltage source of value VO and the voltage VO is only transmitted to point A when the photoresistor PR2 receives a light pulse. The photoresistor control can only be an optical control. Under the action of a light flash, the photoresistor P.R2 works like a switch in the closed state. When it does not receive a light flash, the photo-resistance has a characteristic little different from that of a reverse photodiode.

 When the low-capacity element is constituted by an optically controlled photo-resistance, the high-capacity element can be constituted by a photodiode, as illustrated in FIG. 7 or by a photo-resistance.

 It is understood that in the foregoing, we have not considered all the possibilities for producing photosensitive elements of low and high capacity with all the required characteristics.

 The invention naturally relates to photosensitive devices of the matrix type having numerous rows and columns and to the linear photosensitive devices, obtained for example from the matrix device of FIG. 1 while keeping only one column.

 In FIGS. 4a, b and c, and their description, a method of reading a photosensitive device according to the invention has been envisaged.

Other reading methods can be envisaged.

 In particular when using the photosensitive device according to the invention in radiology, the light information generally arrives in the form of periodic flashes on the whole of the device, as illustrated in FIG. 8a. As in the process illustrated in FIGS. 4a, b and c, two successive readings of the same line, for example the line Im in FIG. 8c, are separated by an integration period ti and only one line is read at the same time, while the other lines are in the integration period. Between the reading of the last line of a frame and that of the first line of the following frame, a dead time c # 3 is created during which a pulse is delivered which makes it possible to trigger the flash of light - see figure 8b.

For the use of the device according to the invention in radiology, one can either cover the photosensitive device with a scintillator which converts the X-rays into radiation detected by the semiconductor used to make the device, or make the photosensitive device on a semiconductor ray sensitive
X, such as thick layer selenium arsenide.

 Figures 9a, b, c and d illustrate another method of reading a photosensitive device according to the invention. This process differs from that illustrated in FIGS. 8a, b and c only because it is sought to reduce the integration time t. to reduce the effects of the dark current from photodiodes.

 The means of sequential addressing of the lines sends a voltage pulse VO on all the lines of the matrix, before the arrival of the light flash - see FIGS. 9a and b -. A device will be described hereinafter with reference to FIG. 10 allowing these voltage pulses VO to be generated simultaneously on all the lines of the device. The arrival of these voltage pulses VO causes the end of the integration period in progress for all the lines of the device. Once the light flash applied to the device, all the lines of the device are in the integration period and the lines are read one after the other, see Figure 9c. We see in Figure 9d, what reduction in integration time has been made for the line 1m compared to the operation of Figure 8c.

 FIG. 10 describes an embodiment of a circuit sequentially addressing each line of photosensitive elements for the purpose of reading it and sending a voltage pulse VO simultaneously on all the lines of the device.

This circuit comprises a logic shift register 5 controlled by at least one clock H. In the example of FIG. 10, this register comprises three outputs R1 to R3. Transistors li to 13 are controlled by the outputs R1 to R3 and connected between a voltage VO and an output of the addressing circuit S1 to S3. Between each output of the circuit and a VCOm voltage, connect a resistor
R01 to R03 which imposes the voltage Vcom on the outputs of the circuit connected to lines which are not read.

As long as the signal R1 is not at the high level, the transistor is blocked and the restoring resistance imposes the voltage V on the output S1. The voltage Vcom is generally the reference voltage, that is to say the mass of the device. When the signal R1 is at the high level, the voltage V is found on the output
o
To accelerate the return to Vcom of the lines when their reading is finished, there is arranged in the embodiment of FIG. 10 a transistor J1 to J3 in parallel on the restoring resistors.

The transistors J1 to J3 are of the same type as the transistors I1 to I3 but they are controlled by the following output of the register.

Thus transistor J1 is controlled by output R2, transistor 32 is controlled by output R3
When the output R1 is at the high level, the voltage VO is found on the output S1 and the transistor Jl is blocked.

 When the output R1 goes to the low level, the output R2 goes to the high level and turns on the transistor Jl 'the voltage V is found on the output Sl.

 It is also possible to use transistors 11 to 13 and J1 to J3 of the same type, but by causing the transistors J1 to 33 to be controlled by the complementary outputs of the register. Thus, the transistor II is controlled by the output R1 and the transistor J1 by the complementary output R1 and so on.

 It is also possible to use transistors li to 13 and J1 to 33 which are complementary. In this case, the transistors 11 and J1 are controlled by the same output of the register, the same for the transistors 12 and J2 ... Thus, for example, the transistor 11, is on, while the transistor J1 is blocked.

 The transistors used can be MOS transistors or TFT for example.

To apply a pulse of voltage Vo on all the lines of the photosensitive device, it is sufficient to superimpose this pulse VO on the voltage V and not to carry any of the outputs
R1 to R3 at the high level.

 According to a variant of the reading methods illustrated by FIGS. 8a, b, and c and 9a, b, c, d, the lines of the device are read in an order chosen according to the image analyzed, and not according to an order predetermined for example from top to bottom of the image.

Thus, one can reduce the effects of the dark current on the area of the image considered to be the most interesting.

 Another variant of the reading method illustrated by FIGS. 9a, b, c, d aims to reduce the time necessary for reading the photosensitive elements by using reading pulses of a level V1 higher than VO. It is then necessary to carry out a leveling of the photosensitive elements by an optical flash before processing the following image. Figures 11a and b are identical to Figures 9a and b. On the other hand in FIG. 11c, it has been shown that the reading of the line lm is done using voltage pulses of amplitude V1 greater than VO.

 It was also indicated that an optical upgrade precedes the processing of a new image.

 We will now describe by way of example a few methods of manufacturing devices according to the invention.

 One of these methods will be described with reference to Figures 12a and b, sectional view and top view of the device.

 A layer of insulating material 6 is used, which serves as a support. It is necessary to use a transparent material if one wishes to illuminate the photosensitive elements through this support 6. One can use for example glass, quartz ...

 A conductive deposit 7 is produced which is etched in wide strips.

 Another insulating deposit 8 is produced which is etched in narrow strips, perpendicular to the wide strips obtained previously.

 A conductive deposition 9 is produced and it is etched in narrow bands included in the bands by isolating 8.

 A nip 10 semiconductor deposition is carried out and blocks are etched therein in contact with both a conductive strip 7 and a conductive strip 9.

 The thickness of the lower layer n is chosen to be sufficiently small so as not to create a significant leak between the conductive strips 7 and 9.

 On the other hand, the upper layer p must be sufficiently conductive to be equipotential and make the connection between the photodiodes d and D.

 In FIG. 12a, the photodiodes d and D are shown schematically in order to indicate their location.

 The photodiode d is produced by the nip deposit in the area where the deposit n which constitutes its cathode is in contact with the connection 9.

It is connected to photodiode D by the p-type layer of the nip deposit. Photodiode D is formed by the nip deposit, in the area where deposit n which constitutes its cathode is in contact with a connection 7.

 The structure thus obtained can optionally be encapsulated by an insulating deposit 11, for example made of nitride, silica or polyimide.

 You can use a pin deposit instead of a pin deposit. The practical production of photosensitive elements is simple when using a photosensitive semiconductor in a thin layer, of pin or nip type, such as for example amorphous silicon or chalcogenides. It is the semiconductor which determines the spectral sensitivity band of the device. The use of silicon gives a spectral band corresponding approximately to the visible radiation.

 In Figure 12b, the column connections 7 are horizontal and the line connections 9 are vertical.

 FIG. 13 differs from FIG. 12b only in a structural modification intended to reduce the parasitic capacitance which exists in the process illustrated by FIGS. 12a and b between the conductors 7 and 9 through the insulator 8.

 The solution proposed in FIG. 13 consists in the zones where the conductor 7 is opposite the insulator 8 and the conductor 9, to shrink the conductor 7, as well as the nip or pin layer 10 which covers it.

 The method described with reference to FIGS. 12 and 13 can be used to produce photosensitive elements, no longer consisting of photodiodes but of photo resistors.

 Instead of a pin or nip deposit, a deposit is produced giving photo-resistances which must be covered by a conductive deposit which must be transparent to light at the level of the low-capacity photo-resistance to allow its optical control, whereas it must be opaque to light at the level of the photo-resistance of high capacity. Indium tin oxide or ITO can be used, for example, for the transparent conductive deposit and any metal for the opaque conductive deposit.

 The radiation to be analyzed in this case comes from the bottom of the device on the side of the transparent insulating support.

 Referring to Figures 14a and b, sectional view and top view, we will describe another method of manufacturing the device according to the invention in the case where each photosensitive element comprises two photodiodes, in series and head-to-tail , but which are superimposed. The two photodiodes do not receive the same illumination. To cancel the currents injected into the columns, one can play on the respective thicknesses of the photodiodes by increasing the thickness of the photodiode located in second position on the path of the optical radiation and which is therefore less illuminated, so as to increase its absorption.

 A conductive deposit 13 is made on a transparent insulating support 12, such as glass, quartz, which makes it possible to light either from above or below, or on an insulating support such as ceramic which requires lighting by the top.

 The conductive deposit 13 is etched in narrow bands.

 A deposition 14 is made of photosensitive semiconductor in thin layers, such as amorphous silicon.

 In this case, a pinip stack is produced and etched to delimit the photosensitive elements.

 The etching must be deep enough to isolate between them the n layers of each photosensitive element. It can be continued up to the support 12 as illustrated in FIG. 14a.

 The low-capacity photodiodes are in contact by their anode with a conductive strip 13.

 The intermediate layer n of the ninip deposit is sufficiently doped and sufficiently thick to constitute an equipotential which connects the low and high capacity photodiodes.

 The lower layer p of the pinip deposits must be sufficiently resistant so that the active part of the photodiodes d is limited to the zones where this layer p is in contact with the conductive electrodes 13.

 An insulating layer 15 is then deposited, for example in intrinsic silicon, in silicon nitride Si3N4, Si N, in silicon oxide SiOx, SiO2.

 Large openings are made on this insulator 15 above the photosensitive elements. These openings delimit the high capacity photodiodes.

 A conductive deposit 16 is produced, engraved in wide strips crossed with respect to the conductive strips 13.

 The conductive strips 16 are in contact with the high-capacity photodiodes.

 The light to be analyzed can be sent not through the support layer 12 but through the conductive strips 16, which must then be chosen to be transparent.

 A semiconductor deposit can be made either of the nipin or pinip type.

 Referring to figures Ifia and b, sectional view and top view, we will describe a last manufacturing process which compared to the two other processes described, with the advantage of not requiring a good control of the resistivity of the layers doped 10 or p, as well as the advantage of requiring only three pin or nip layers as regards the photosensitive material deposited.

 Is carried out on an insulating support, possibly transparent, 17 a conductive deposit 18 etched in strips and rectangles.

 A photosensitive semiconductor deposition is carried out in thin layers 19, of the pin or nip type and it is etched so that the semiconductor deposition is located on the conductive strips and rectangles 18. The high-capacity photodiodes are thus produced on the rectangles and those of low capacity on the bands.

 An insulating deposit 20 is produced which is opened above the low and high capacity photodiodes. This insulating deposit is also opened on a part of the conducting rectangles 18 which has not received a semiconductor deposit 19.

 A conductive deposit 21 is then produced which on the one hand connects the top of the low capacity photodiodes, located on the strips 18, to the rectangles 18 which carry the high capacity photodiodes. Thus, the photodiodes are connected in series. On the other hand, the conductive deposit 21 interconnects the high capacity photodiodes, by their upper part, constituting narrow bands 21 crossed with respect to the bands 18. Thus, the high capacity photodiodes are connected to the columns.

 The manufacturing methods described above in the case of photosensitive elements comprising two photodiodes in series and head to tail can be adapted to the various embodiments of the photosensitive elements which have been described previously.

Claims (22)

 1. Photosensitive device in the solid state, comprising - a network of horizontal connections or lines (him, 12, 13) and at least one vertical connection or column (cl, c2, C3) crossing the lines; - a photosensitive element connecting each line and each column which intersect; - Means (5) ensuring the sequential addressing of each line of photosensitive elements for reading; - A circuit (2) ensuring the reading and the multiplexing of the columns, characterized in that each photosensitive element consists of first and second elements connected in series, the first so-called low-capacity element having a capacity at least substantially ten times lower than that of the second element known as of high capacity, in that at least each element of high capacity is photosensitive, the photosensitivity of an element resulting in a leakage current of this element and in that each element of low capacity is connected to a line, and functions as a switch, closed only when the line is addressed by the addressing means.  2. Device according to claim 1, characterized in that the photosensitive elements consist of two photodiodes (d, D) mounted head to tail.  3. Device according to claim 2, characterized in that the two photodiodes td, D) differ only in their surfaces.  4. Device according to claim 1, characterized in that the first elements of low capacity consist of a photodiode (d).  5. Device according to claim 1, characterized in that the first elements of low capacity, are constituted by a photoresistor (P.R2).  6. Device according to claim 5, characterized in that the second high capacity elements consist of a photo diode (D).  7. Device according to one of claims 4 or 5, characterized in that the second high-capacity elements consist of a photo-resistance (P.R1).  8. Device according to one of claims 2 or 4, characterized in that the addressing means are constituted by a shift register (5) whose outputs are connected to the lines, and which carries a control pulse.  9. Device according to one of claims 2, 4 or 5, characterized in that the addressing means are means for sequential optical control of the elements of low capacity of each line.  10. Device according to one of claims 1 to 9, characterized in that the photosensitive elements, çs are produced on a photosensitive semiconductor in thin layers.  11. Device according to claim 10, characterized in that this semiconductor is amorphous silicon.  12. Method for reading a photosensitive device according to one of claims 1 to 11, characterized in that it consists in sending to the low capacity elements (d) of a line which it is desired to read pulses of control ensuring the closing of the switches constituted by these elements.  13. Reading method according to claim 12, characterized in that: - the light information is permanently sent to the photosensitive device, - two successive readings of the same line are separated by an integration period (ti), - one reads only one line at a time, while the other lines are in the integration period.  14. Reading method according to claim 13, characterized in that: - the light information is sent in the form of periodic flashes over the entire device; - two successive readings of the same line are separated by an integration period (ti) - one reads only one line at a time while the other lines are in the integration period; - between the reading of the last line of a frame and that of the first line of the following frame, a dead time (4) is created during which a pulse is delivered which makes it possible to trigger the light flash.  15. Reading method according to claim 12, characterized in that: - the light information is sent in the form of periodic flashes over the entire device and before the arrival of each flash, the addressing means generate pulses of voltage applied simultaneously to all the lines of the device which cause the end of the integration periods in progress for all the lines of the device, - one reads only one line at a time, while the other lines are in period of integration, - between the reading of the last line of a frame and that of the first line of the following frame, a dead time is created (;;) during which a pulse is delivered which makes it possible to trigger the light flash.  16. Method according to one of claims 14 or 15, characterized in that the lines of the device are read in an order chosen according to the image analyzed.  17. Method according to one of claims 14 to 16, characterized in that: - the photosensitive elements are read by means of pulses of amplitude voltage (V1) greater than that (VO) of the applied voltage pulses simultaneously to all the lines of the device, - a light flash ensures a leveling of the photosensitive elements before the voltage pulses are applied simultaneously to all the lines of the matrix.  18. A method of manufacturing a device according to one of claims 1 to 11, characterized in that it comprises the following steps: a) a conductive deposit (7) is produced on a transparent insulating support (6) and etching the conductive deposit in wide bands, b) an insulating deposit (8) is engraved on the conductive deposit (8) etched in narrow bands perpendicular to the wide bands already obtained, c) another conductive deposit (9) is etched in bands narrow included in the bands by insulating (7), d) a photosensitive semiconductor deposition is made in a thin layer (10), of pin or nip type, and blocks are etched there in contact with both a conductive strip (7) and with a conductive strip (.9).  19. Method according to claim 18, characterized in that during steps a and d, the conductive deposit (7) and the semiconductor deposit (10) are etched so as to reduce the surface area of conductors (7), covered with semiconductor ( 10) in areas where the conductors (7) are opposite the insulator (8) and the conductor (9).  20. Method according to one of claims 18 or 19, characterized in that during step d there is no longer a semiconductor deposit of the pin or nip type, but a deposit giving photoresistors, which is covered by a transparent conductive layer, light at the low-capacity photo-resistance and opaque to light at the high-capacity photo-resistance.  21. A method of manufacturing a photosensitive device according to one of claims 1 to 11, characterized in that it comprises the following steps: a) a conductive deposit (13) is produced on an insulating support (12) and etch the conductive deposit in narrow bands, b) a photosensitive semiconductor deposit (14) is produced in thin layers, of the pinip or nipin type, and it is etched so as to isolate at least the n or p layers from the photosensitive elements, c) an insulating layer (15) is deposited in which openings are made to delimit the high-capacity photodiodes, d) a conductive deposit (16) is etched in wide strips crossed with respect to the conductive strips (13).  22. A method of manufacturing a photosensitive device according to one of claims I to 11, characterized in that it comprises the following steps: a) a conductive deposit (18) is etched in an insulating support (17) strips and rectangles, b) a photosensitive semiconductor deposition is carried out in thin layers (19) and it is etched so as to locate it on the rectangles and on the strips and to produce high and low capacity photodiodes, c) an insulating deposit (20) open is produced above the photodiodes as well as on a part of the rectangles (18) which has not received a semiconductor deposit (19), d) a conductive deposit (21) is formed which on the one hand connects the top of the high capacity photodiodes carried by the rectangles (18) and which on the other hand connects the top of the low capacity photodiodes carried by the strips (18) to the rectangles (18).