PN junction chemical sensor

Abstract

A sensor device (100, 2800) for detecting particles, the sensor device (100, 2800) comprising a substrate (102), a first doped region (104) formed in the substrate (102) by a first dopant of a first type of conductivity, a second doped region (106, 150) formed in the substrate (102) by a second dopant of a second type of conductivity which differs from the first type of conductivity, a depletion region (108) at a junction between the first doped region (104) and the second doped region (106, 150), a sensor active region (110) adapted to influence a property of the depletion region (108) in the presence of the particles, and a detection unit (112) adapted to detect the particles based on an electric measurement performed upon application of a predetermined reference voltage between the first doped region (104) and the second doped region (106, 150), the electric measurement being indicative of the presence of the particles in the sensor active region (110).

Claims

1. A sensor device for detecting particles, the sensor device comprising: a substrate; a first doped region formed in the substrate by a first dopant of a first type of conductivity; a second doped region formed in the substrate by a second dopant of a second type of conductivity which differs from the first type of conductivity, wherein the second doped region includes a lower doped region of the second conductivity type and a higher doped region of the second conductivity type; a depletion region at a junction between the first doped region and the second doped region, wherein the lower doped region is adjacent to the first doped region and located between the first doped region and the higher doped region; a sensor active region configured and arranged to influence a property of the depletion region in the presence of the particles; and a detection circuit configured and arranged to detect the particles based on an electric measurement performed upon application of a predetermined reference voltage between the first doped region and the second doped region, the electric measurement being indicative of current passing through the depletion region while the presence of the particles in the sensor active region influence the current passing through the depletion region.

2. The sensor device according to claim 1, wherein a substrate configured and arranged to receive a sample, in the form of a liquid or solid substance, in an aperture of the substrate; wherein the sensor active region is configured and arranged to access the sample in the aperture and influence the property of the depletion region in the presence of the particles; and the first doped region is a p-doped region and the second doped region is an n-doped region.

3. The sensor device according to claim 1, wherein the sensor active region is configured and arranged to influence a value of a breakdown voltage of an arrangement formed by the first doped region, the second doped region and the depletion region in the presence of the particles.

4. The sensor device according to claim 1, wherein the substrate includes a dopant having the first conductivity type; and the sensor active region comprises capture-particles configured and arranged for attaching with the particles.

5. The sensor device according to claim 4, wherein the sensor active region comprises a dielectric layer between the capture particles and the depletion region.

6. The sensor device according to claim 1, wherein the detection circuit is configured and arranged to detect the particles by performing the electric measurement at or around a breakdown voltage, as the predetermined reference voltage, of an arrangement formed by the first doped region, the second doped region and the depletion region.

7. The sensor device according to claim 1, wherein the detection circuit is configured and arranged for operating an arrangement formed by the first doped region, the second doped region and the depletion region with a reverse bias.

8. The sensor device according to claim 1, wherein the detection circuit is configured and arranged to detect the particles based on a shift of a breakdown voltage of an arrangement formed by the first doped region, the second doped region and the depletion region with a reverse bias.

9. The sensor device according to claim 1, wherein the detection circuit is configured and arranged to detect the particles by: determining the predetermined reference voltage as a breakdown voltage of an arrangement formed by the first doped region, the second doped region and the depletion region in the absence of the particles; measuring an electric current at the breakdown voltage of the arrangement in the absence of the particles; measuring, in the presence of the particles, an electric current passing through the depletion region at the breakdown voltage of the arrangement determined in the absence of the particles; and comparing the electric current measured in the presence of the particles and in the absence of the particles.

10. The sensor device according to claim 1, configured and arranged to detect electrically charged particles.

11. The sensor device according to claim 1, wherein the substrate comprises a plurality of trenches filled at least partially with dielectric material and extending from the first doped region to the second doped region.

12. The sensor device according to claim 11, comprising an electrically conductive inlay in the dielectric material of at least a part of the plurality of trenches.

13. The sensor device according to claim 11, wherein the plurality of trenches is part of the sensor active region.

14. The sensor device according to claim 2, configured and arranged in that the sample including the particles is free from a contact with electrical connections of the sensor device.

15. The sensor device according to claim 1, wherein the property is a size of the depletion region.

16. The sensor device according to claim 1, wherein the depletion region has a concentration of charge carriers which is one of: at least 10.sup.2 times, at least 10.sup.3 times, and at least 10.sup.4 times smaller than a concentration of charge carriers in the first doped region and/or in the second doped region.

17. A sensor device for detecting particles, the sensor device comprising: a substrate; a first doped region formed in the substrate by a first dopant of a first type of conductivity; a second doped region formed in the substrate by a second dopant of a second type of conductivity which differs from the first type of conductivity, wherein the second doped region comprises a highly doped region and a lowly doped region; a depletion region at a junction between the first doped region and the second doped region, wherein the lowly doped region is arranged adjacent to the first doped region to form the depletion region at the junction with the first doped region; a sensor active region configured and arranged to influence a property of the depletion region in the presence of the particles; and a detection circuit configured and arranged to detect the particles based on an electric measurement performed upon application of a predetermined reference voltage between the first doped region and the second doped region, the electric measurement being indicative of current passing through the depletion region while the presence of the particles in the sensor active region influence the current passing through the depletion region.

18. The sensor device according to claim 17, wherein the sensor active region is provided directly on the depletion region.

19. The sensor device according to claim 1, configured and arranged as one of a biosensor device, a chemical sensor device, a pH sensor device, an enzymatic sensor device, a DNA sensor device, and a protein sensor device.

20. A method of detecting particles, the method comprising: providing a depletion region at a junction between a first doped region formed in a substrate by a first dopant of a first type of conductivity and a second doped region formed in the substrate by a second dopant of a second type of conductivity which differs from the first type of conductivity, wherein the second doped region includes a lower doped region and a higher doped region, and the lower doped region is adjacent to the first doped region and located between the first doped region and the higher doped region; providing access of a fluidic sample comprising the particles to a sensor active region on the depletion region by back grinding the substrate; influencing a property of the depletion region by the presence of the particles; and detecting the particles based on an electric measurement performed upon application of a predetermined reference voltage between the first doped region and the second doped region, the electric measurement being indicative of the presence of the particles in the sensor active region.

21. The method according to claim 20, further comprising providing access of a fluidic sample comprising the particles to a sensor active region by implementing a silicon-on-nothing system.

22. The sensor device according to claim 1, wherein the first and second doped regions have a higher doping concentration than the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

(2) FIG. 1 illustrates a sensor device according to an exemplary embodiment of the invention.

(3) FIG. 2 is a diagram showing an effect of an external potential applied on a dielectric on the current-voltage curve of the diode of FIG. 1.

(4) FIG. 3 shows a cross-section of a conventional high voltage diode.

(5) FIG. 4 shows a top view of the high voltage diode of FIG. 3.

(6) FIG. 5 shows a conventional DIELER diode in a top view.

(7) FIG. 6 shows a cross-section of the DIELER diode of FIG. 5 along a line B-B′.

(8) FIG. 7 shows a cross-section of the DIELER diode of FIG. 5 along a line C-C′.

(9) FIG. 8 shows a conventional DIELER device with field plates.

(10) FIG. 9 shows a conventional FET sensor.

(11) FIG. 10 shows a sensor device according to another exemplary embodiment of the invention.

(12) FIG. 11 shows a sensor device according to another exemplary embodiment of the invention.

(13) FIG. 12 to FIG. 14 show cross-sections of layer sequences providing liquid access by a system of back grinding of the wafer according to an exemplary embodiment of the invention.

(14) FIG. 15 to FIG. 17 illustrate the fabrication of a silicon-on-nothing device according to an exemplary embodiment of the invention.

(15) FIG. 18 to FIG. 21 show the use of the silicon-on-nothing system of FIGS. 15 to 17 to bring a liquid close to a detection electrode according to an exemplary embodiment of the invention.

(16) FIG. 22 to FIG. 25 show cross-sections of a layer sequence during DNA sensing according to an exemplary embodiment of the invention.

(17) FIG. 26, 27, 29, 30 illustrate layer sequences used for explaining a sensor device according to a preferred embodiment of the invention, which is shown in FIG. 28.

DESCRIPTION OF EMBODIMENTS

(18) The illustration in the drawing is schematical. In different drawings, similar or identical elements are provided with the same reference signs.

(19) Referring to FIG. 1, a sensor device 100 for detecting biological particles according to an exemplary embodiment of the invention will be explained.

(20) The sensor device 100 comprises a silicon substrate 102. A p.sup.+-doped region 104 is formed in a surface portion of the substrate 102 by a p-dopant implantation. A second doped region 106, namely an n.sup.+-doped region, is formed in another surface portion of the substrate 102 by implanting an n-dopant of an n-type of conductivity which differs from the p-type of conductivity of the p.sup.+-doped region 104.

(21) Between the p.sup.+-doped region 104 and the n.sup.+-doped region 106, an optional lowly doped region 150 is formed in a surface portion of the substrate 102, which has an n.sup.−-dopant concentration that is significantly smaller than the dopant concentrations in the first and second doped regions 104, 106. According to semiconductor physical laws, a depletion region 108 is formed at a junction between the two oppositely doped regions 104, 150. For an embodiment that omits the lowly doped region 150, reference is made to FIG. 28.

(22) A sensor active region 110 is configured to influence a property of the depletion region 108 (or more precisely of the diode structure 104, 106, 108, 150), particularly a size of the depletion region 108 which may have an impact on a current-voltage correlation of the diode-like configuration, in the presence of electrically charged particles to be detected. As can be taken from FIG. 1, the sensing region 110 can be exactly on top of the depletion region 108.

(23) A detection unit 112 is provided which may be a CPU (Central Processing Unit) or microprocessor which may be adapted to detect the particles based on an electric measurement performed upon application of a predetermined reference voltage between the first doped region 104 and the second doped region 106, the electric measurement being indicative of the presence of the particles in the sensor active region 110. The measurement may be performed at a predetermined reference voltage, particularly at a breakdown voltage estimated in the sample free state of the sensor device 100. It is possible to evaluate the breakdown voltage and the I(V) curves, which change when the size of the depletion region 108 changes. More particularly, the detection unit 112 is adapted to apply a predetermined reference voltage between the first doped region 104 and the second doped region 106 and to perform an electric measurement to detect the particles based on an evaluation of the electric measurement being sensitive to the property of the depletion region 108.

(24) The sensor active region 110 is provided on or over the depletion region 108. The sensor active region 110 comprises capture particles 114 adapted for attachment with the particles to be detected. Furthermore, a dielectric layer 116 is provided between the capture particles 114 and the depletion region 108. The detection unit 112 controls the voltage V of a voltage source 120. Further, the detection unit 112 is in bidirectional communication with a current detector 122 or Amperemeter. The detection unit 112 is further coupled to an input/output unit 124. Via the input/output unit 124, a user may enter control commands or may receive detection results from the detection unit 112.

(25) During operation, the detection unit 112 may be adapted for detecting the particles by first determining the predetermined voltage as a breakdown voltage of the diode formed by the first doped region 104 and the second doped region 106 in the absence of the particles. Then, the Amperemeter 122 at the breakdown voltage of the arrangement may measure an electric current in the absence of the particles. Subsequently, the Amperemeter 122 in the presence of the particles may measure the electric current. This measurement may be performed at the breakdown voltage of the arrangement determined beforehand in the absence of the particles. Subsequently, the detection unit 112 may compare the electric current values measured in the presence of the particles and in the absence of the particles, and may derive a sensor result therefrom.

(26) Thus, a sensing device 100 is provided using a shift in the breakdown voltage of a reverse biased diode 104, 106, 108, 150.

(27) The breakdown voltage of the pn diode 104, 106, 108, 150 in reverse bias is closely related to the size of the diode depletion region 108. The depletion region 108 size, and thus the breakdown voltage, can be increased by adding an optional lowly doped region 150 between the p.sup.+ region 104 and the n.sup.+ region 106. Furthermore, the breakdown voltage can be tuned by applying an external potential to this lowly doped region. Therefore, a change in the external potential on top of the lowly doped region 108 induced by the attachment of charged particles to the capture particles 114 will modify the breakdown voltage of the diode 104, 106, 108, 150.

(28) According to an exemplary embodiment of the invention, the above-described effect may be used to detect the presence of charged particles. This will be described referring to FIG. 2.

(29) FIG. 2 is a diagram 200 having an abscissa 202 along which the voltage is plotted in Volt. Along an ordinate 204, the current is plotted in Ampere. The voltage V.sub.BDO is shown as well in FIG. 2 for the diode 104, 106, 108, 150 of FIG. 1. When the voltage at the dielectric layer 116 is 0 Volt, a characteristic curve 206 is measured. When the voltage V.sub.diel at the dielectric layer 116 is −100 mV, a second curve 208 is measured. As can be taken from FIG. 2, after attachment and before attachment of charged particles to the capture particles 114, the current value at the voltage V.sub.BDO significantly differs (compare I.sub.after, I.sub.before).

(30) Before the application of the charged particles, a first measurement 206 determines a voltage V.sub.BD0, close the breakdown voltage of the diode 104, 106, 108, 150 and where the current increases a lot as a function of the potential, and measures the current at V.sub.BD0. After the application of the charged particles, a second measurement 208 determines the current also at V.sub.BD0. Because the measurements occur in the range of the breakdown voltage, the simulations show that the difference in the current between both measurements can be of several orders of magnitude.

(31) In the following, some basic recognitions of the present inventors will be explained based on which exemplary embodiments of the invention have been developed.

(32) Even if a sensor according to an exemplary embodiment of the invention is clearly not a high-voltage device, the high-voltage devices are a background of the invention because a sensor according to an exemplary embodiment of the invention makes use of the techniques (lowly-doped region, modification of the size of the depletion region by an external potential) that are used in their field.

(33) A main challenge in high voltage devices is to make diodes that can withstand a high voltage difference without breakdown. This increase in the breakdown voltage is often achieved by integrating a large lowly doped drift region between the p-type and n-type regions, see FIG. 3, FIG. 4.

(34) FIG. 3 shows a cross-sectional view 300 of a conventional diode having a substrate 302, a p.sup.+-region 304, an n.sup.+-region 306 and an n.sup.−-doped region 308.

(35) FIG. 4 shows a plan view 400 of the diode of FIG. 3.

(36) If the dimensions and doping of the region 308 are adequately tuned, this increase in the breakdown voltage can be enhanced by the RESURF effect. Furthermore, applying a potential to the n-region may further modify the breakdown voltage of the diode.

(37) DIELER diodes are disclosed as such in WO 2006/136979. Trenches filled with an isolator and located as shown in FIG. 5 to FIG. 7 will increase further the breakdown voltage of the diode. An alternative to the DIELER is to only partially fill the trenches with oxide and thus create conducting field plates in the trenches.

(38) FIG. 5 shows a top view 500 of a DIELER diode 500. As compared to FIG. 4, a plurality of trenches 502 is provided.

(39) FIG. 6 shows a cross-sectional view 600 along a line B-B′ of FIG. 5, and FIG. 7 shows a cross-sectional view 700 along a line C-C′ of FIG. 5.

(40) FIG. 8 shows a three-dimensional view 800 of a conventional DIELER diode 800. A buried oxide layer 802 is shown. An n.sup.−-external drain region 804 is provided thereon. A first n.sup.+ source/drain region 806 and a second n.sup.+ source/drain region 808 are shown. Furthermore, a gate 810 is shown. Trenches 812 are formed having a dielectric layer 814 and an electrically conductive field plate 816. Furthermore, a p-well 818 is shown.

(41) FIG. 9 shows a conventional FET sensor 900. A counter electrode 902 is coupled to a voltage source V.sub.CE 904, which voltage source is further coupled to a transistor 906 having a gate being coupled to a detection electrode 908. A further voltage source 910 V.sub.ds is shown as well.

(42) A lot of the FET sensors are built in the same way like shown in FIG. 9. The liquid containing the species to detect is in contact with the counter electrode 902 (sometimes called reference electrode) and a detection electrode 908. The detection electrode 908 is connected to the gate of the transistor 906. Several detection systems exist to detect different events, like pH changes in the solution, or attachment of biological particles, but all have in common that they result in a change in the gate potential of the transistor. This change in the gate potential induces a change in the source/drain current of the transistor.

(43) To summarize, the detection of an event resulting in a change in the gate potential is made by a measurement in a change of the source/drain current.

(44) In the following, an embodiment of the invention having a DIELER diode with field plates will be explained.

(45) FIG. 10 shows a sensor device 1100 according to an exemplary embodiment of the invention.

(46) The sensor device 1100 comprises a plurality of trenches 1102 filled partially with dielectric material 1104 and extending from the first doped region 104 via the lowly-doped region 108 to the second doped region 106. The sensor device 1100 comprises an electrically conductive inlay 1106 in the dielectric material 1104 of the plurality of trenches 1102. The trenches 1102 are part of the sensor active region 110.

(47) FIG. 10 shows a scenario in which particles to be detected 1120 are provided functionally coupled to the field plates 1106.

(48) In the sensor device 1200 according to another exemplary embodiment of the invention shown in FIG. 11, the particles 1120 are provided within the trenches 1102.

(49) The charged particles 1120 to detect can either be on top of fields plates 1106 (FIG. 10) or the STI 1104 can be empty and the charged particles 1120 come in the place of the field plates 1106 (see FIG. 11). There, the area coverage by the external potential induced by the charge attached will even be larger than with the “basic” diode. Thus a higher difference in the breakdown voltage may be possible.

(50) The embodiment of FIG. 1 (simple diode) is very easy to build with doping a piece of monocrystalline silicon or by using the technology of high-voltage CMOS.

(51) Taking into account the fact that the liquid should not be in contact with the electrical connections, several solutions for this problem are possible. It is possible to give to the liquid a direct access to the detection electrode or to build the interconnect structure of the circuit and to have the electrode included in this interconnect structure.

(52) Alternatively, back grinding of the wafer is possible, see FIG. 12 to FIG. 14, in which the embedded p-region 1402 can be there or not.

(53) FIG. 12 shows a cross-sectional view 1400 of a layer sequence according to an exemplary embodiment of the invention.

(54) The layer sequence 1400 includes a further p-conductive layer 1402 below an interconnect structure 1404 which includes contacts 1406, 1408 to the first and second doped regions 104, 106, respectively. Thus, FIG. 12 shows a wafer with an interconnect structure.

(55) FIG. 13 shows a layer sequence 1500, in which the wafer 102 is grinded to provide liquid access.

(56) FIG. 14 shows a layer sequence 1600, in which an oxide layer 1602 is created, and charged particles 1604 are deposited thereon.

(57) Further alternatively, “silicon on nothing” vias may be implemented. This embodiment may use a silicon-on-nothing method, like the one shown in FIG. 15 to FIG. 17.

(58) FIG. 15 shows an image 1700 regarding spherical ESS.

(59) An image 1800 shown in FIG. 16 relates to pipe shaped ESS.

(60) An image 1900 shown in FIG. 17 relates to plate shaped ESS.

(61) Regarding FIG. 15 to FIG. 17, reference is made to T. Sato et al., Japanese Journal of Applied Physics Part 1—Regular Papers Short Notes & Review Papers 43, 12 (2004), for a more detailed explanation.

(62) FIG. 18 to FIG. 21 illustrate the use of a silicon-on-nothing system to bring the liquid close to the detection electrode. Thus, FIG. 18 to FIG. 21 show the fabrication of a silicon-on-nothing device 2300.

(63) As can be taken from FIG. 18, a hole 2000 is formed in the substrate 102.

(64) An interconnect structure 1404 is then formed, as can be taken from FIG. 19. As can be taken from FIG. 20, vias 2200 are etched, and a silicon oxide layer 1602 is created in the hole 2000. FIG. 21 then shows a liquid motion direction 2302.

(65) A sensor according to an exemplary embodiment of the invention is capable to measure the difference between two situations: a reference situation and detection itself.

(66) 1) In the reference situation, no liquid or a reference liquid is put on the dielectric, the reference curve I.sup.0(V) of the reversed diode is measured and the breakdown potential V.sub.BD0 is determined. The manufacturer may do such a reference measurement and the result may be provided to the customer.

(67) 2) The detection itself may be performed after the deposition of the liquid to test on the detection electrode. The measurement can either be a scan that provides a curve I(V) to compare to the reference curve I.sup.0(V), or just a measurement of the current at a potential close to V.sub.BD0.

(68) Because the potential with the highest difference of current is between breakdown potentials of the situations with no particles and with a lot of particles (see FIG. 2) it is also possible to do a pre-test to get an idea of this ideal potential and then do the real measurement. The currents obtained in the simulations are so low (for instance <10.sup.−5A) that the breakdown should not destroy the diode.

(69) The measurement protocol may be the following:

(70) a) Measurement of the curve I(V) with a reference liquid, determination of V.sub.BD0. b) Measurement with a solution highly concentrated in particles, determination of V.sub.BD1.

(71) c) Measurement of the current with a probe particle at a potential in the middle of V.sub.BD0 and V.sub.BD1. With this measurement, one may know which electrode in the array is functionalized by the probe particle. The point of the whole experiment is actually to detect the presence or absence of the target particle complementary of this one.

(72) d) Measurement with the target particle. If it is not complementary to the other, it will not attach it and measurement c) and d) will give the same result. If it attaches, its presence may modify the current at the voltage.

(73) FIG. 22 to FIG. 25 illustrate an exemplary embodiment of particles sensing, these particles being DNA.

(74) In FIG. 23, a solution with highly concentrated DNA 2500 is measured. In FIG. 24, a measurement with known strand of DNA 2600 is performed. In FIG. 25, attachment between the strands 2600 and test DNA 2700 occurs.

(75) Referring to FIG. 28, a sensor device 2800 for detecting biological particles according to a preferred embodiment of the invention will be explained.

(76) FIG. 26, FIG. 27, FIG. 29 and FIG. 30 illustrate layer sequences used for explaining a working principle of the sensor device 2800, which is shown in FIG. 28.

(77) The embodiment of FIG. 28 omits the central lowly-doped region n.sup.− 150 of FIG. 1.

(78) As can be taken from FIG. 26 and FIG. 27, a diode is formed of a p-doped region 104 and an n-doped region 106. The fact that these regions 104, 106 are in contact with each other creates at their junction a depletion region 108. The breakdown voltage of the diode depends on the size of this depletion region 108.

(79) The principle of the embodiment of FIG. 28 can work with such a diode (i.e, a diode without lowly-doped region 150 in the middle, compare FIG. 1) since the presence of particles may influence the size of the depletion region 108 and thus the breakdown voltage of the diode. FIG. 28 shows that the central lowly-doped region 150 is not needed.

(80) The breakdown voltage depends on the size of the depletion region 108 which in turn depends on the doping concentration. Therefore, a way to increase the breakdown voltage of a diode is to add a lowly doped region 150 (n.sup.− for example but it can be p.sup.−) between the p and n regions 104, 106, see FIG. 1, FIG. 29, FIG. 30. In that case, the depletion region 108 will be localized at the junction between the p and n regions 104, 150 and it may extend more in the n.sup.− region 150 than in the p region 104 (see FIG. 30). It may sometimes be so large that it extends to the n region 106.

(81) Advantages of the embodiment of FIG. 1 with a central lowly-doped region 150 are:

(82) the depletion region 108 size and thus the breakdown voltage can be tuned more easily by changing the doping and size of the middle region 150, and

(83) since the depletion region 108 is larger, the particles have more place to attach, so more particles can attach and the detection may be easier. Finally, it should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The words “comprising” and “comprises”, and the like, do not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.