Patent Publication Number: US-9897568-B2

Title: NW-FET sensor comprising at least two distinct semiconducting nanowire detectors

Description:
TECHNICAL DOMAIN AND PRIOR ART 
     The invention relates to the domain of NW-FET (“Nano-Wire Field Effect Transistor”) sensors, the operating principle of which is similar to that of ISFET (“Ion Sensitive Field Effect Transistor”) type sensors used particularly to detect electrically charged particles in a fluid, for example to make a pH meter. 
     ISFET type devices are used to detect a concentration of charges in a solution. This variation in the concentration of charges acts like a variation in the gate potential of such an FET device, thus modulating the channel current in a nanowire of the ISFET device. 
       FIG. 1  diagrammatically shows an ISFET type device  10 . The device  10  comprises, on a dielectric layer  12  corresponding for example to the buried dielectric layer of an SOI substrate, a drain region  14 , a source region  16  and a semiconducting nanowire, for example silicon, forming a channel  18  and extending between the drain and source regions  14 ,  16 . A dielectric layer  20  is placed on the dielectric layer  12  and covers the source and drain regions  14 ,  16  and the channel  18 . An opening  22  passes through the dielectric layer  20  and opens up on the channel  18 . The opening  22  forms a microfluid cavity in which a fluid  24  is introduced. When an electric charge  26  present in the fluid  24  is located in the microfluid cavity, close to the channel  18 , a variation of the current circulating in the channel  18  is then obtained by polarisation of the channel  18  when this electric charge moves and modifies the distance between the electric charge  26  and the channel  18 . This current circulating in the channel  18  also varies when the number of charges present close to the channel  18  is modified. 
     Such devices can also be made collectively in the form of a detection matrix to increase the density of sensors per unit area. This is very advantageous in the case of detection of a single charge  26  carried by a particle in the solution  24 , so as to increase the probability of detection of the charge by one of the sensors. In this case of the detection of a single particle, it is also necessary to address each sensor individually in the matrix formed, which is equivalent to being able to identify the sensor in which the channel current varies. 
     However, the density with which these devices can be made is limited, particularly due the dimensions of the drain and source regions  14 ,  16  that cannot be reduced below a certain value because these regions must be electrically connected through vias to address the devices individually. These vias are defined by openings made in the drain and source regions  14  and  16  above the lower metallic contact zones formed in a stack under the dielectric layer  12 . This stack can be obtained after the SOI substrate is transferred (and then thinned) on the “Back-end of Line” type substrate of a CMOS circuit. 
     PRESENTATION OF THE INVENTION 
     Therefore there is a need to disclose a solution to improve the density at which electrical charges or electrically charge molecules can be detected, and also to propose a solution for improving the density of a matrix of NW-FET sensors in which the sensor within this matrix in which there is a variation of the channel current can be identified (sensor addressing function). 
     One embodiment discloses an NW-FET sensor for this purpose, comprising at least: 
     first and second semiconducting nanowires forming two distinct channels; 
     a first semiconducting portion forming a source region, of which a first part doped with a first type of conductivity (in other words an acceptor or donor type doping) is connected to a first end of the first semiconducting nanowire, and a second end of which doped with a second type of conductivity opposite the first type of conductivity (in other words an acceptor doping if the first part is a donor type doping, or a donor doping if the first part is an acceptor type doping) is connected to a first end of the second semiconducting nanowire; 
     a second semiconducting portion forming a drain region, of which a first part doped with the first type of conductivity is connected to a second end of the first semiconducting nanowire, and a second end of which doped with the second type of conductivity is connected to a second end of the second semiconducting nanowire; 
     a first electrical contact placed on the first semiconducting portion and electrically connected to the first and second parts of the first semiconducting portion; 
     a second electrical contact placed on the second semiconducting portion and electrically connected to the first and second parts of the second semiconducting portion; 
     In such a sensor, the first and second semiconducting nanowires form two detectors associated with the same source and drain regions. These two detectors can be addressed individually from each other due to the different doping of the different parts of the semiconducting portions forming the source and drain regions. Due to sharing of the source and drain regions by the two detectors formed, the area occupied by these two detectors is equivalent to the area occupied by a single sensor according to prior art forming a single detector because this area is dictated by the dimensions of the source and drain regions. Thus, the density at which electrical charges or electrically charged molecules can be detected by such sensors is much than the density that can be obtained by sensors according to prior art. 
     The differentiation or addressing made between the first and second semiconducting nanowires is achieved by opposite doping of the semiconducting parts forming their drain and source regions and the fact that single pole transport of charges with opposite natures takes place in each channel thus formed. Thus, transport in the channel associated with drain and source regions with donor type doping, or N doping (denoted NW-N), is preponderantly by electron type carriers (negative charge carrier in a semiconductor). Transport in the channel associated with drain and source regions with acceptor type doping, or P doping (denoted NW-P), is preponderantly by hole type carriers (positive charge carrier in a semiconductor). 
     In the same way as the polarisation conditions of a MOSFET transistor, a difference of potentials between the drain and source regions (Vds) can modify the current in the channel of each detector. In the disclosed sensor, if a positive voltage Vds is applied (which means that a potential applied on the drain is higher than the potential applied on the source), the majority electrons in the NW-N detector channel tend to displace from the source to the drain, and majority holes in the channel of the NW-P detector also tend to displace from the source to the drain. Depending on the conventions, two currents are formed in opposite directions (the current being in the same direction as holes and the opposite direction to electrons) in the two channels of the sensor and therefore potentially a very small total current passing through the structure (under specific polarisation conditions). 
     Unlike a conventional MOSFET transistor in which a gate potential Vgs is applied to define the static operation of the transistor, the gate potential in this case is defined by the charges present close to one or more channels or by the position of a single charge above one of the channels. Thus, if a negative charge approaches the channel of the NW-P type detector and under the Vds conditions described above, this movement of the charge tends to increase the majority holes current described above, while the majority electrons current in the NW-N type detector is less affected or is not affected at all. This modifies the global current passing through the structure, in other words the global current in the two channels of the sensor. It is possible to use this principle to identify which nanowire detected displacement of a charge, depending on the nature of the variation of the global current and knowing the polarity of this charge. A distinction can thus be made between the following cases (using the conventions mentioned above): 
     when a negative charge approaches the NW-P detector, the channel current in the NW-P detector increases and the global current decreases; 
     when a negative charge approaches the NW-N detector, the channel current in the NW-N detector decreases and the global current increases; 
     when a positive charge approaches the NW-P detector, the channel current in the NW-P detector decreases and the global current increases; 
     when a positive charge approaches the NW-N detector, the channel current in the NW-N detector increases and the global current decreases; 
     Such a sensor is advantageously used in the framework of a sequential 3D co-integration of sensors on a CMOS control and read circuit, and in which nanowires in the sensors are addressed individually by the CMOS circuit both by independent connections between sensors with two semiconducting nanowires as described above and by a physical differentiation within source and drain regions obtained due to different doping in the first and second parts of the source and drain regions to which the nanowires are connected. 
     The first and second semiconducting nanowires and the first and second semiconducting portions can be parts of a single continuous semiconducting element. The expression “single continuous semiconducting element” refers to a semiconductor portion not interrupted by a vacuum or by another material, in other words forming a single semiconducting part. 
     The first part of the first semiconducting portion can be separated from the second part of the first semiconducting portion by a distance equal to at least about 20 nm or equal to at least about 250 nm and/or the first part of the second semiconducting portion can be separated from the second part of the second semiconducting portion by a distance equal to at least about 20 nm or equal to at least about 250 nm. 
     The NW-FET sensor may be such that: 
     the semiconductor of the first and second nanowires is intrinsic (forming a sensor with intrinsic channels), or 
     the first semiconducting nanowire is doped with a first type of conductivity with a doping level less than the doping level of the first parts of the first and second semiconducting portions, and the second semiconducting nanowire is doped with a second type of conductivity with a doping level less than the doping level of the second parts of the first and second semiconducting portions, or 
     the first semiconducting nanowire is doped with the second type of conductivity and the second semiconducting nanowire is doped with the first type of conductivity. 
     A specific doping of the channels of the NW-N and NW-P nanowires may be applied in order to maximise the sensitivity of the sensor, in other words to maximise the global current variation under the effect of the displacement of an electric charge close to one of the sensor channels: if the channel of the NW-P detector is doped as P type, forming a P+/P/P+ type assembly with the source and drain regions, in other words such that the drain and source regions (P+ doping) are doped more than the channel (P doping), the detector has a much higher current than a device with an undoped channel. 
     Similarly, such a current increase is obtained in the channel of the NW-N detector comprising a (source+drain+channel) assembly doped with an N+/N/N+ type. 
     By adjusting the different N+/N/N+ and P+/P/P+ doping levels of channels of NW-N and NW-P detectors respectively and remaining within low Vds polarisation conditions, a structure can be obtained with a low global current in the presence of a non-zero Vds and with no applied gate potential. 
     The configuration in which the first and second nanowires are doped with the same type of conductivity as the source and drain regions associated with them has the advantage of increasing the current level circulating in the sensor when there is no applied gate potential, in other words increasing the intensity of the detection signal output by the sensor. 
     The NW-FET sensor can also comprise at least one first dielectric layer on which the semiconducting nanowires and the first and second semiconducting portions are placed. 
     In this case, the NW-FET sensor may also comprise at least one gate electrode placed in the first dielectric layer, facing at least one of the first and second semiconducting nanowires. With such a gate, the sensor can be polarised through the application of an electrical polarisation potential on the gate, at an operating point optimised for the sensitivity/noise ratio. 
     The NW-FET sensor may also comprise: 
     a substrate located under the first dielectric layer and comprising a CMOS control and read circuit; 
     electrical interconnection levels located in the first dielectric layer and electrically connected to the CMOS control and read circuit (levels forming a “Back-End-Of-Line” (BEOL) part); 
     at least two electrically conducting vias each passing through one of the first and second semiconductor portions and a part of the first dielectric layer, and electrically connecting the first and second electrical contacts to one of the electrical interconnection levels. 
     Another embodiment applies to a detection device comprising several NW-FET sensors like those described above, in which each of the NW-FET sensors or groups of NW-FET sensors are arranged adjacent to each other forming a detection matrix. 
     In each group of NW-FET sensors, one of the first and second semiconducting portions of a first of the NW-FET sensors in said group may be common to at least one second of the NW-FET sensors in said group and may comprise at least one third part doped with the first type of conductivity connected to one of the first and second ends of the first semiconducting nanowire of the second NW-FET sensor in said group, and a fourth part doped with the second type of conductivity connected to one of the first and second ends of the second semiconducting nanowire of the second NW-FET sensor in said group. In such a configuration, two sensors share one of their source and drain regions, which can further increase the detection density that can be achieved compared with sensors according to prior art. These two sensors can be seen as being connected to each other in series. 
     Each group of NW-FET sensors may comprise four first NW-FET sensors and eight second NW-FET sensors such that one of the first and the second semiconducting portions of the first NW-FET sensors is in common and the other of the first and second semiconducting portions of each is in common with two of the other second NW-FET sensors and such that one of the first and second semiconducting portions of each of the second NW-FET sensors is in common with another of the second NW-FET sensors. This configuration further optimises the space occupied by twelve NW-FET sensors and further improves the detection density that can be obtained. 
     A method of making an NWFET sensor is also disclosed, comprising steps to: 
     dope first regions of a semiconducting layer with a first type of conductivity, and second regions of the semiconducting layer with a second type of conductivity opposite the first type of conductivity; 
     etch the semiconducting layer, forming:
         first and second semiconducting nanowires forming two distinct channels of the NW-FET sensor;   a first semiconducting portion forming a source region of the NW-FET sensor, of which a first part included in one of the first doped regions is connected to a first end of the first semiconducting nanowire, and a second part included in one of the second doped regions is connected to a first end of the second semiconducting nanowire;   a second semiconducting portion forming a drain region of the NW-FET sensor, of which a first part included in another of the first doped regions is connected to a second end of the first semiconducting nanowire, and a second part included in another of the second doped regions is connected to a second end of the second semiconducting nanowire;       

     make a first electrical contact on the first semiconducting portion and electrically connected to the first and second parts of the first semiconducting portion (for example formed by a metallic deposit that partially covers the first and second doped parts of the first semiconducting portion); 
     make a second electrical contact on the second semiconducting portion and electrically connected to the first and second parts of the second semiconducting portion (for example formed by a metallic deposit that partially covers the first and second doped parts of the second semiconducting portion); 
     The method may also include the implementation of steps before the doping step of the first and second semiconducting regions, to: 
     make a substrate comprising a CMOS control and read circuit; 
     make electrical interconnection levels in a first dielectric layer arranged on the substrate, the electrical interconnection levels being electrically connected to the CMOS control and read circuit; 
     make the semiconducting layer on the first dielectric layer, for example after the transfer of an SOI substrate onto the CMOS substrate formed and thinning of the stack thus obtained. 
     The method may also comprise application of a step, after the step to etch the semiconducting layer, to make at least two openings each passing through one of the first and second semiconducting portions and a part of the first dielectric layer and such that they open up on one of the levels of electrical interconnections, and then a step to deposit an electrically conducting material in the two openings and on the first and the second semiconducting portions, forming the first and second electrical contacts and two electrically conducting vias each passing through one of the first and second semiconducting portions and a part of the first dielectric layer, and electrically connecting the first and second electrical contacts to said one of the electrical interconnection levels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This invention will be better understood after reading the description of example embodiments given purely for information and in no way limitative with reference to the appended drawings on which: 
         FIG. 1  shows an ISFET type device according to prior art; 
         FIGS. 2 and 3  show a sectional side view and a top view respectively of a first embodiment of an NW-FET sensor; 
         FIGS. 4 and 5  show a sectional side view and a top view respectively of a second embodiment of an NW-FET sensor; 
         FIG. 6  shows a top view of a first embodiment of a detection device comprising NW-FET sensors with a common semiconducting portion; 
         FIG. 7  shows a top view of a second embodiment of a detection device comprising NW-FET sensors with common semiconducting portions; 
         FIGS. 8 to 36  show steps in a method of making an NW-FET sensor according to a particular embodiment. 
     
    
    
     Identical, similar or equivalent parts of the different figures described below have the same numeric references to facilitate the comparison between different figures. 
     The different parts shown on the figures are not necessarily all at the same scale, to make the figures more easily understandable. 
     The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other. 
     DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS 
     Refer firstly to  FIG. 2  that shows a side sectional view of a first embodiment of an NW-FET sensor  100 , and to  FIG. 3  that shows a top view of the sensor  100 . 
     The sensor  100  comprises a substrate  102  forming a CMOS back-end part electrically connected to the active part of the sensor  100 , in which a CMOS read and control circuit is made, but is not shown in  FIGS. 2 and 3 . A first dielectric layer  103  is arranged on the substrate  102  and corresponds to the ILD (Inter-Layer Dielectric) layers between which electrical interconnection levels are made, also not shown on  FIGS. 2  et  3 , electrically connecting the CMOS read and control circuit to the active part of the sensor  100  (and to other sensors similar to the sensor  100 , not shown on  FIGS. 2 and 3  and also made on the same substrate  102 ). The last level of electrical interconnections (the level located closest to the active part of the sensor  100 , or the level located furthest from the substrate  102 ) comprises connection pads electrically connected to the active part of the sensor  100  through conducting vias passing particularly through a part of the first dielectric layer  103 . Two connection pads  104 ,  106  of the last electrical interconnections level are shown on  FIGS. 2 and 3 . 
     The sensor  100  comprises an active semiconducting part, for example comprising silicon, placed on the substrate  102  and comprising a first portion  108  forming a source region, and a second portion  110  forming a drain region of the sensor  100 . A first part  112  of the first portion  108  is doped with a first type of conductivity, in this case P type, and a second part  114  of the first portion  108  is doped with a second type of conductivity opposite the first type of conductivity, in this case N type. The two parts  112 ,  114  are for example spaced from each other by a distance of at least 20 nm, or at least about 250 nm, so that opposite dopings made in the two parts  112 ,  114  can be clearly differentiated and are not superposed. Similarly, a first part  116  of the second portion  110  is doped with the first type of conductivity (P type), and a second part  118  of the second portion  110  is doped with the second type of conductivity (type N). The two parts  116 ,  118  are at a spacing from each other, like parts  112 ,  114 . 
       FIG. 3  and the following figures symbolically show doped parts  112 ,  114 ,  116  and  118  each symbolically surrounded by a rectangle box shown in dashed lines to clearly identify these doped parts of portions  108 ,  110  from other undoped parts of these portions  108 ,  110 . These boxes represent the initially doped regions in the semiconducting layer that was used to make portions  108 ,  110 . 
     The active part of the sensor  100  also comprises two nanowires  120 ,  122  at a spacing from each other and forming two distinct channels of the sensor  100 . A first end of the first nanowire  120  is connected to the first part  112  of the first portion  108  and a second end of the first nanowire  120  is connected to the first part  116  of the second portion  110 . Moreover, a first end of the second nanowire  122  is connected to the second part  114  of the first portion  108  and a second end of the second nanowire  122  is connected to the second part  118  of the second portion  110 . The nanowires  120 ,  122  thus form distinct channels but are connected to source and drain regions common to these two channels. Dopings and activation annealings are done before an ILD deposition. 
     A first electrical contact  124 , in this case metallic, is placed on the first portion  108  and forms an electric contact common to the first and second parts  112 ,  114  of the first portion  108 . A second electrical contact  126 , also of the metallic type, is placed on the second portion  110  and forms an electric contact common to the first and second parts  116 ,  118  of the second portion  110 . The first electrical connection  124  is electrically connected to the connection pad  104  through a first conducting via  128  passing through the first portion  108  and a part of the first dielectric layer  103  located between the connection pad  104  and the first portion  108 . The second electrical connection  126  is electrically connected to the connection pad  106  through a second conducting via  130  passing through the second portion  110  and a part of the first dielectric layer  103  located between the connection pad  106  and the second portion  110 . 
     Although the electrical contacts  124 ,  126  are common to the two detectors formed by the two nanowires  120 ,  122 , these two detectors can be addressed individually due to the different dopings of the parts  112 ,  114 ,  116 ,  118  of the portions  108 ,  110  to which the nanowires  120 ,  122  are connected. 
     The electrical operating principle of the sensor  100  is as follows. When a positive or negative non-zero Vds polarisation voltage is applied between portions  108  and  110 , a current circulates in the two detectors of the sensor  100 . When the parts  112 ,  116  are P doped and the parts  114 ,  118  are N doped, electrons circulate predominantly in the nanowire  122  and holes circulate predominantly in the nanowire  120 . When Vds&gt;0, electrons and holes move from portion  108  (the source) towards portion  110  (the drain). When Vds&lt;0, electrons and holes move from portion  110  towards portion  108 . 
     Therefore, regardless of whether Vds is positive or negative, the global current circulating in the sensor  100  is zero if the numbers of carriers per unit time transiting in the nanowires  120 ,  122  (which takes account particularly of concentrations and mobility of charge carriers) are identical in parts  112 ,  114 ,  116 ,  118 . When an electrical charge moves or is detected above one of the two nanowires  120 ,  122 , this global current becomes non-zero or has a detectable variation because one of the currents of electrons or holes is modified. This current is read by the CMOS control and read circuit that is electrically connected to the detectors through electrical contacts  124 ,  126 , conducting vias  128 ,  130  and electrical interconnection levels connecting these vias to the CMOS control and read circuit. 
     Therefore with such a sensor  100  allows the formation of, while occupying the same or a very similar semiconducting area as that occupied by the device  10  according to prior art described above (since the critical dimensions of the sensor  100  and the device  10  are the dimensions of the portions  108 ,  110 ), two detectors that operate independently of each other and for which the activity of a charge on one of the two nanowires can be identified by the variation of the global current in the structure and the polarity of the charge. Therefore, integration of such sensors  100  into a detection matrix containing several of these sensors  100  can increase the density of the detectors present on this matrix, because the device  10  according to prior art only forms a single detector for the entire area occupied by the device  10 , while the sensor  100  forms two distinct devices. 
       FIGS. 4 and 5  show a sectional side view and a top view respectively of a second embodiment of the NW-FET sensor  100 . 
     Unlike the sensor  100  described above with reference to  FIGS. 2 and 3 , the sensor  100  according to this second embodiment also comprises an additional metallic portion  132  forming part of the last level of electrical interconnections and used as a gate electrode for the two detectors formed by the sensor  100 . This metallic  132  portion is electrically connected to the CMOS control and read circuit that generates an electrical field in the nanowires  120 ,  122  when a gate potential is applied to this portion  132 , so that the detectors containing the nanowires  120 ,  122  can be polarised at a required operating point or polarisation point. By judiciously choosing this operating point, the sensor  100  can be made to operate such that its sensitivity/noise ratio is improved (the sensitivity of the sensor relates to the value of its transconductance). 
     On the example in  FIGS. 4 and 5 , the portion  132  is common to the two nanowires  120 ,  122 . As a variant, two metallic portions can be made side by side, each under one of the nanowires  120 ,  122 , so that the two detectors of the sensor  100  can be polarised differently. According to another variant, it is possible that the portion  132  is placed facing only one of the two nanowires  120 ,  122 , and in this case only one of the detectors of the sensor  100  can be preponderantly polarised due to the portion  132 . 
     In the two embodiments described above, the nanowires  120 ,  122  of the sensors  100  comprise the intrinsic semiconductor. According to a first variant that can be applied to either of the embodiments described above, it is possible that the semiconductor of these nanowires  120 ,  122  is doped with the same type as the semiconducting parts, forming the source and drain regions to which the nanowires are connected. For example, considering the first embodiment of the sensor  100  shown on  FIGS. 2 and 3 , it is possible that the first nanowire  120  that is connected to the P doped parts  112 ,  116  is also formed from a P doped semiconductor, and that the second nanowire  122  that is connected to the N doped parts  114 ,  118  is also formed from an N doped semiconductor. In this case, the doping level of parts  112 ,  114 ,  116 ,  118  is higher than the doping level of nanowires  120 ,  122  (for example with the P doped nanowire  120  and P+ doped parts  112 ,  116 , and the N doped nanowire  122  and the N+ doped parts  114 ,  118 ). This first variant is advantageous because it provides optimum sensitivity without any gate polarisation other than that of the charge to be detected, while assuring a very low current Id and therefore low consumption. The principle is based on the fact that the two nanowires  120 ,  122  have maximum transconductance at Vgs=0. 
     In other cases, the nanowires  120 ,  122  have transconductances for non-zero Vgs values and are polarised to improve the sensitivity of the detector. 
     According to a second variant, the semiconductor in the nanowires  120 ,  122  can be doped with the type opposite to the type with which the semiconductor of the semiconducting parts  112 ,  114 ,  116 ,  118  is doped. For example, considering the sensor  100  according to the first embodiment shown on  FIGS. 2 and 3 , it is possible that the first nanowire  120  that is connected to the P doped parts  112 ,  116  is formed from an N doped semiconductor and that the second nanowire  122  that is connected to the N doped parts  114 ,  118  is formed from a P doped semiconductor. 
     The advantage of these first and second variants is that the required polarisation point can be adapted depending on the sensitivity and the noise generated by the structure. 
     Regardless of which embodiment or variant is considered, several sensors  100  are advantageously made on the same substrate  102  and are placed adjacent to each other forming a detection matrix of a detection device  200 . 
     The density with which the sensors  100  can be integrated into a detection matrix can be further increased by making the sensors  100  such that one of the two portions  108 ,  110  is common to one or several other sensors  100  of the device  200 . 
       FIG. 6  shows a top view of a first embodiment of such a detection device  200  comprising several sensors  100  forming a detection matrix. Only two of the sensors, references  100 . 1  and  100 . 2 , of the device  200  are shown on  FIG. 6 . In this first embodiment of the detection device  200 , the sensors  100  form two groups of sensors  100  sharing their second portion  110 . On  FIG. 6 , the second portion  110  is common to the two sensors  100 . 1  and  100 . 2  and forms a drain region common to these two sensors  100 . 1  and  100 . 2 . 
     The first sensor  100 . 1  comprises the same elements as the sensor  100  described above with reference to  FIGS. 2 and 3 , in other words a first semiconducting portion  108 . 1  including first and second parts  112 . 1  and  114 . 1  doped differently to each other, a second semiconducting portion  110  comprising first and second parts  116 . 1  and  118 . 1  doped differently from each other, first and second nanowires  120 . 1  and  122 . 1  the ends of which are connected to parts  112 . 1 ,  114 . 1 ,  116 . 1  and  118 . 1 , electrical contracts  124 . 1  and  126  located on the portions  108 . 1  and  110 , conducting vias  128 . 1  and  130  and the other elements of the back-end part of the sensor  100 . 
     However, unlike the second portion  110  of the sensor  100  described above with reference to  FIGS. 2 and 3 , the second portion  110  shown on  FIG. 6  also comprises a third part  116 . 2  doped with the first type of conductivity and a fourth part  118 . 2  doped with the second type of conductivity, in addition to the first and second parts  116 . 1 ,  118 . 1 . These third and fourth parts  116 . 2 ,  118 . 2  are at a spacing from each other in the same way as the first and second parts  116 . 1 ,  118 . 1 . The second electrical contact  126  is placed on these four parts  116 . 1 ,  118 . 1 ,  116 . 2  and  118 . 2  of the second portion  110  and therefore forms an electrical contact common to the first, second, third and fourth parts  116 . 1 ,  118 . 1 ,  116 . 2 ,  118 . 2  of the second portion  110 . 
     The second sensor  100 . 2  also comprises a first semiconducting portion  108 . 2  that comprises a first part  112 . 2  doped with the first type of conductivity and a second part  114 . 2  doped with the second type of conductivity, these two parts  112 . 2 ,  114 . 2  being at a spacing from each other in a similar manner to parts  112 . 1  and  114 . 1  of portion  108 . 1 . 
     The second sensor  100 . 2  also comprises a first nanowire  120 . 2  and a second nanowire  122 . 2  forming two distinct channels of the second sensor  100 . 2 . A first end of the first nanowire  120 . 2  is connected to the third part  116 . 2  of the second portion  110  and a second end of the first nanowire  120 . 2  is connected to the first part  112 . 2  of the first portion  108 . 2  of the second sensor  100 . 2 . A first end of the second nanowire  120 . 2  is connected to the fourth part  118 . 2  of the second portion  110  and a second end of the second nanowire  120 . 2  is connected to the second part  114 . 2  of the first portion  108 . 2  of the second sensor  100 . 2 . 
     Finally, the first portion  108 . 2  of the second sensor  100 . 2  is covered by an electrical contact  124 . 2  forming an electrical contact common to the first and second parts  112 . 2 ,  114 . 2  of the portion  108 . 2 . This electrical contact  124 . 2  is electrically connected to an additional connection pad formed in the last electrical interconnections level through a conducting via  128 . 2  passing through this first portion  108 . 2  and a part of the first dielectric layer  103  located between this additional connection pad and this first portion  108 . 2 . 
     The four detectors formed by these two sensors  100 . 1  and  100 . 2  can be addressed individually due to the different dopings of the parts  112 ,  114 ,  116 ,  118  to which the nanowires  120 ,  122  of each of the sensors  100 . 1 ,  100 . 2  are connected, even though the second region  110  forms a drain region common to these four detectors (since polarisation of one of the sensors  100 . 1 ,  100 . 2  can be chosen depending on the source region on which the polarisation voltage is applied). 
     As a variant of the first embodiment of the device  200  previously described with reference to  FIG. 6 , it is possible that the doping types of the different parts of the semiconducting regions of the second sensor  100 . 2  are inverted from those described above, in other words the parts  116 . 2  and  112 . 2  of the second sensor  100 . 2  are doped with the second type of conductivity and the parts  118 . 2  and  114 . 2  of the second sensor  100 . 2  are doped with the first type of conductivity. 
     In the configuration shown on  FIG. 6 , the two sensors  100 . 1  and  100 . 2  are arranged to be in parallel with each other, in other words such that the nanowires  120 ,  122  of the two sensors  100 . 1 ,  100 . 2  have their large dimensions approximately along the same direction. As a variant, the two sensors  100 . 1  and  100 . 2  can be arranged differently relative to each other. For example, it is possible that the sensors  100 . 1  and  100 . 2  are arranged approximately perpendicularly to each other, in other words the largest dimensions of the nanowires  120 . 1 ,  122 . 1  of the first sensor  100 . 1  are oriented approximately perpendicular to the nanowires  120 . 2 ,  122 . 2  of the second sensor  100 . 2  (the nanowires  120 ,  122  of the two sensors being in the same plane). In this case, in the second portion  110 , the third and fourth parts  116 . 2  and  118 . 8  at the portion  110  may be located on a side adjacent to the side on which the first and second parts  116 . 1 ,  118 . 1  are located, rather than on a side opposite to the side on which the first and second parts  116 . 1 ,  118 . 1  are located. 
     Furthermore, in the configuration shown on  FIG. 6 , the sensors  100  of the device  200  form groups of two sensors connected to each other in series and sharing the same portion of semiconductor forming a source or drain region of these sensors. As a variant, the sensors  100  can form groups of more than two sensors sharing their semiconducting portion in pairs. 
       FIG. 7  is a top view of a second embodiment of a detection device  200  comprising a set of sensors  100  each forming two detectors that can be addressed independently, and each comprising semiconducting portions common to one, two or three other sensors  100 . 
     Thus, in the configuration shown on  FIG. 7 , the device  200  comprises four first sensors  100 . 1 ,  100 . 2 ,  100 . 3  and  100 . 4  with a common first semiconducting portion  108 . 1 . Therefore this first portion  108 . 1  comprising eight differently doped parts in pairs to which the nanowires of the four first sensors  100 . 1  to  100 . 4  are connected. The device  200  also comprises eight second sensors  100 . 5  to  100 . 12 . Each of the second semiconducting portions  110 . 1 ,  110 . 2 ,  110 . 3  and  110 . 4  of the first four sensors  100 . 1  to  100 . 4  is common to two of the second sensors  100 . 5  to  100 . 12 . Therefore each of the second portions  110 . 1  to  110 . 4  comprises six parts differently doped in pairs to which the nanowires of one of the four first sensors  100 . 1  to  100 . 4  and two of the eight sensors  100 . 5  to  100 . 12  sensors are connected. Thus on  FIG. 7 , the second portion  110 . 1  of the first sensor  100 . 1  is common to the second sensors  100 . 5  and  100 . 6 , the second portion  110 . 2  of the first sensor  100 . 2  is common to the second sensors  100 . 7  and  100 . 8 , the second portion  110 . 3  of the first sensor  100 . 3  is common to the second sensors  100 . 9  and  100 . 10 , and the second portion  110 . 4  of the first sensor  100 . 4  is common to the second sensors  100 . 11  and  100 . 12 . Finally, each of the second sensors  100 . 5  to  100 . 12  comprises a first semiconducting portion  108 . 2 ,  108 . 3 ,  108 . 4  or  108 . 5  common to another of the second sensors  100 . 5  to  100 . 12 . Thus on  FIG. 7 , the first portion  108 . 2  is common to the second sensors  100 . 6  and  100 . 7 , the first portion  108 . 3  is common to the second sensors  100 . 8  and  100 . 9 , the first portion  108 . 4  is common to the second sensors  100 . 10  and  100 . 11 , and the first portion  108 . 5  is common to the second sensors  100 . 12  and  100 . 5 . 
     The second embodiment of the device  200  shown on  FIG. 7  is particularly advantageous due to the high detection density that can be obtained with the twelve sensors  100 . 1  to  100 . 12  thus made, due to the fact the that the first and second semiconducting regions  108 ,  110  of these sensors are put in common. This principle can be extended to a larger matrix comprising a larger number of sensors. 
     The device  200  as described previously with reference to  FIGS. 6 and 7  can be made from sensors  100  corresponding to any one of the previously described embodiments or variants of the sensor  100 . 
     We will now describe an example embodiment of a method for making a sensor  100  with reference to  FIGS. 8 to 36 . 
     The CMOS Back-End part of the sensor  100  is made firstly in the substrate  102 , in other words the CMOS transistors of the control and read circuit, and the level(s) of electrical interconnections made in the first dielectric layer  103  located on the substrate  102 . Only the two connection pads  104 ,  106  of the last electrical interconnections level are shown on  FIG. 8 . The first dielectric layer  103  and the connection pads  104 ,  106  are covered with a first bonding layer  136 , for example comprising silicon oxide deposited by a TEOS precursor. 
     At the same time as the CMOS Back-End of the sensor  100  is being made, another substrate is prepared so that a semiconducting layer that will used to make the active part of the sensor  100  can be transferred onto the substrate  102 . On  FIG. 9 , this other substrate corresponds to an SOI substrate comprising a solid semiconducting layer  138 , a buried dielectric layer  140  and a surface semiconducting layer  142  that in this case corresponds to a thin layer of silicon, less than about 10 μm thick. The surface layer  142  is covered with a second bonding layer  144 , for example comprising silicon oxide deposited by a TEOS precursor. 
     As shown on  FIG. 10 , the two previously made substrates are assembled to each other through their bonding layers  136 ,  144  fixed to each other for example by direct bonding. 
     The assembly obtained is then thinned by grinding and then by dry etching, eliminating the solid layer  138  and the buried dielectric layer  140 , thus exposing the surface semiconducting layer  142 . As a variant, it is possible that part of the thickness of the buried dielectric layer  140  can be kept to act as a hard mask later. 
     As shown on  FIG. 12  that is a top view of the surface layer  142 , a first step in the implantation of dopants according to the first type of conductivity is made in the first regions  105  and  107  of the layer  142  each including one of the future first parts  112  and  116  of the first and second semiconducting portions  108 ,  110  of the sensor  100 .  FIG. 13  shows that a second implantation of dopants with the second type of conductivity is made in the second regions  109  and  111  of the layer  142  each including one of the future second parts  114  and  118  of the first and second semiconducting portions  108 ,  110  of the sensor  100 . 
     Lithography and etching are then done on the surface layer  142  to define and form the nanowires  120 ,  122  and the semiconducting portions  108 ,  110  ( FIG. 14 ). On  FIG. 14 , the regions  105 ,  107 ,  109  and  111  are shown symbolically to clearly show the lithography and etching done. 
     When the nanowires  120 ,  122  comprise semiconductor doped with the same type of dopants as the regions to which the nanowires are connected, the steps described above with reference to  FIGS. 12 to 14  can be replaced by those described below with reference to  FIGS. 15 to 19 . 
     As shown on  FIG. 15 , a first implantation of dopants with the first type of conductivity is made in a region  146  of the layer  142  including the future first parts  112  and  116  and the first nanowire  120 . The concentration of dopants implanted in the region  146  corresponds to the required concentration of dopants in the first nanowire  120 . 
     A second implantation of dopants with the second type of conductivity is made in another region  148  of the layer  142  including the future second parts  114  and  118  and the second nanowire  122  ( FIG. 16 ). The concentration of dopants implanted in the region  148  corresponds to the required concentration of dopants in the second nanowire  122 . 
     A third implantation of dopants with the first type of conductivity is made in the first regions  105  and  107  regions of the layer  142  including the future first parts  112 ,  116  of the first and second semiconducting portions  108 ,  110  of the sensor  100 , and such that these first regions  105  and  107  comprise a higher doping level than the semiconducting portion that will form the first nanowire  120  ( FIG. 17 ). 
     A fourth implantation of dopants with the second type of conductivity is made in the second regions  109  and  111  of the layer  142  including the future second parts  114 ,  118  of the first and second semiconducting portions  108 ,  110 , and such that these second regions  109  and  111  comprise a higher doping level than the semiconducting portion that will form the second nanowire  122  ( FIG. 18 ). 
     Lithography and etching are then done on the surface layer  142  to define and form the nanowires  120 ,  122  and the semiconducting portions  108 ,  110  ( FIG. 19 ). On  FIG. 19 , the regions  105 ,  107 ,  109  and  111  are shown symbolically to clearly show the lithography and etching done. 
     As an alternative, when the nanowires  120 ,  122  comprise a semiconductor doped with a type different from the type of the semiconductor of the parts to which the nanowires are connected, steps similar to those described with reference to  FIGS. 15 to 19  are used, however with different types of doping from the dopings done in the regions  146 ,  148  and the dopings made afterwards in the regions  105 ,  107 ,  109  and  111 . 
     In all cases, implanted dopings are then activated, for example by annealing the sensor  100 . This activation is applied with a heat budget compatible with the materials used. 
     The steps described with reference to  FIGS. 12 to 19  are used collectively for all sensors  100  made on the same substrate, in other words in the same surface layer  142 . 
       FIGS. 20 and 21  show an example geometry of the active part of the sensor  100 . 
     Each of the semiconducting portions  108 ,  110  comprises a first region with a square section for which the dimensions of the sides are L 1  and W 4 , for example equal to about 700 nm. The parts  112  and  114  of the portion  108  are made in second regions each with a rectangular section and located on the same side as the first region of the portion  108 , and for which the dimensions of the sides are for example L 2 =120 nm and W 2 =150 nm. Similarly, the parts  116  and  118  of the portion  110  are made in second regions each with a rectangular section and located on the same side as the first region with a square section of the portion  110 , and for which the dimensions of the sides are for example L 2 =120 nm and W 2 =150 nm. The first nanowire  120  is made in a third region with a rectangular section joining the second regions of the parts  112  and  116  for which the side dimensions are for example L 3 =100 nm and W 1 =50 nm. Similarly, the second nanowire  122  is made in a third rectangular section joining the second regions of the parts  114  and  118  for which the side dimensions are for example L 3 =100 nm and W 1 =50 nm. 
     The different dopings of the parts  112 ,  114 ,  116 ,  118  and possibly of the nanowires  120 ,  122  are applied in regions for example like those shown on  FIG. 21 . The regions  105 ,  107 ,  109  and  111  of parts  112 ,  114 ,  116 ,  118  are each for example rectangular in shape with side dimensions W 5 =200 nm and L 5 =80 nm. Regions  113  and  115  of the nanowires  120 ,  122  are each for example rectangular in shape and with side dimensions W 5 =200 nm and L 4 =120 nm. 
       FIGS. 20  et  21  clearly illustrate the fact that the different regions described above forming the first and second semiconducting nanowires  120 ,  122  and the first and second semiconducting portions  108 ,  110  are parts of the same continuous semiconducting element formed by etching in the semiconducting layer  142 . 
     After the active part of the sensor  100  formed by the portions  108 ,  110  and the nanowires  120 ,  122  have been made, a first passivation layer  150 , for example containing TEOS, is deposed on the entire structure made, in particular covering the active part of the sensor  100  ( FIG. 22 ). 
       FIG. 23  shows a lithography step called a “counter mask” that includes partial etching of the dielectric (with etching depth equal to the thickness of the silicon layer) and then stripping. In defining the mask of this lithography by a negative mask dimension ZACT of −500 nm, the thickness on the dielectric layer to be removed by CMP later is reduced (step described with reference to  FIG. 24 ). This makes the thickness of this dielectric layer more uniform. 
     As shown on  FIG. 24 , CMP is then applied to polish the first passivation layer  150 . 
     Openings  152  are then made through the first passivation layer  150  facing the portions  108 ,  110  so as to access these portions ( FIGS. 25 and 26 ). 
     Other openings  154  are then etched through the portions  108 ,  110  and the bonding layers  136 ,  144 , these openings  154  opening up onto connection pads  104 ,  106  ( FIGS. 27, 28 ). 
     A metallic layer  156  is then deposited on the entire structure, particularly such that the openings  154  are filled with metal from layer  156 , thus forming the conducting vias  128 ,  130  ( FIG. 29 ). The parts of this metallic layer  156  that partially cover the portions  108 ,  110  form electrical contacts  124 ,  126 . 
     Lithography and etching of the metallic layer  156  are then used, eliminating parts of the layer  156  located on the first passivation layer  150  and that do not form part of the electrical contacts  124 ,  126  ( FIGS. 30, 31 ). This etching also electrically isolates the electrical contacts  124 ,  126  from each other by eliminating metallic parts connecting the electrical contacts  124 ,  126  to each other. 
     As shown on  FIG. 32 , a second passivation layer  158 , for example containing TEOS, is deposited over the entire structure. 
       FIG. 33  shows a “countermask” lithography step followed by etching and then stripping. Dimensions are defined relative to the metal level mask. 
     As shown on  FIG. 34 , CMP is then applied to polish the second passivation layer  158 . 
     The device  100  is then completed by making an opening  160  through the passivation layers  150 ,  158  that form a second dielectric layer covering the semiconducting portions  108 ,  110  and the electrical contacts  124 ,  126  until the nanowires  120 ,  122  are reached. The opening  160  thus forms a microfluid cavity in which the fluid comprising electrically charged particles to be detected by the sensor  100  will be introduced to be in contact with the nanowires  120 ,  122 .