EP2092307A1

EP2092307A1 - Semiconductor sensor device, diagnostic instrument comprising such a device and method of manufacturing such a device

Info

Publication number: EP2092307A1
Application number: EP07849347A
Authority: EP
Inventors: Neriman N. Kahya; Erik P. A. M. Bakkers; Thomas Steffen; Lars M. Borgstrom
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2006-12-08
Filing date: 2007-12-06
Publication date: 2009-08-26
Also published as: JP2010511886A; WO2008068721A1; CN101558290A

Abstract

Semiconductor sensor device (10) for sensing a substance (30) comprising a mesa- shaped semiconductor region (11,11') which is formed on a surface of a semiconductor body (12) while a fluid (20) comprising the substance (30) to be sensed can flow along the mesa-shaped semiconductor region (11), wherein the mesa- shaped semiconductor region (11) comprises viewed in a longitudinal direction subsequently a first semiconductor subregion (1) comprising a first semiconductor material, a second semiconductor subregion (2) comprising a second semiconductor material different from the first semiconductor material and a third subregion (3) comprising a third semiconductor material different from the second semiconductor material. According to the invention the first and third semiconductor material comprise an optically passive material and the second semiconductor material comprises an optically active material, the substance (30) to be sensed can change a property of electromagnetic radiation (E) coming from the second subregion (2) and the semiconductor sensor device (10) is formed such that the electromagnetic radiation (E) of which the property has been changed can reach a detector (50). The sensor device (10) according to the invention can be very sensitive, relatively compact and easy to manufacture. The radiation (E) can originate from an external source (40) or can be generated in the device (10).

Description

Semiconductor sensor device, diagnostic instrument comprising such a device and method of manufacturing such a device

FIELD OF THE INVENTION

The invention relates to a semiconductor sensor device for sensing a substance comprising a mesa-shaped semiconductor region which is formed on a surface of a semiconductor body while a fluid comprising a substance to be sensed can flow along the mesa-shaped semiconductor region, wherein the mesa-shaped semiconductor region comprises, viewed in the longitudinal direction, subsequently a first semiconductor subregion comprising a first semiconductor material, a second semiconductor subregion comprising a second semiconductor material different from the first semiconductor material, and a third semiconductor subregion comprising a third semiconductor material different from the second semiconductor material. Mesa-shaped of a region here means that the region forms a protrusion on the surface of the semiconductor body. The protruding may either be in longitudinal or a lateral direction of the body. The invention also relates to a diagnostic instrument comprising such a sensor device and to a method of manufacturing such a semiconductor sensor device. Such a device is very suitable for detecting chemical and/or biochemical substances. In the latter case it can e.g. be used for detecting biomolecules like antigen/antibody bindings, biomolecules and others with a high sensitivity and reproducibility, and thus it can be used advantageously in protein and gene analysis, disease diagnostics and the like. The mesa-shaped semiconductor region may comprise a nano-wire. Here with a nano-wire a body is intended having at least one lateral dimension between 1 and 100 nm and more in particular between 10 and 50 nm. Preferably a nano-wire has dimensions in two lateral directions that are in the said ranges. Its longitudinal dimension may be e.g. between 100 and 1000 nm. With such a device the detection of molecules like chemical substances that are volatile or dissolved in a liquid is also possible, e.g. by introduction of the substance carrying a charge on or in a nano-wire of which the conductivity is thus changed.

BACKGROUND OF THE INVENTION

A device as mentioned in the opening paragraph is known from the United States Patent that has been published under number US 6,882,051 on April 19, 2005. In this document, heterojunction nano-wires are disclosed for use in a chemical sensor(see column 35 line 5). In an example of a heterojunction nano-wire, the latter comprises alternating subregions of Silicon (Si) and Germanium (Ge) (see Fig. 3 and the corresponding parts of the description). In other example of a heterojunction nano-wire, the latter comprises alternating layers of Galliumarsenide (GaAs) and Galliumantimonide (GaSb)(see Fig. 17 and the corresponding part of the description).

A disadvantage of such a device is that its sensitivity is not high enough for certain application. In particular in the medical field, detection of a biochemical compound, in particular a bio molecule, is desired at a very low concentration of such a compound or molecule. It is desirable that the detection can be done, e.g. for detecting a disease, like an infection, at a very early stage in order to act in a prophylactic manner as much as possible. This requires a sensor device with an extremely high sensitivity.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to avoid the above drawback and to provide a semiconductor sensor device, which is suitable for use in the medical field and which possesses a very high sensitivity for the substance to be detected.

To achieve this, a semiconductor sensor device of the type described in the opening paragraph is characterized in that the first and third semiconductor material comprise an optically passive material and the second semiconductor material comprises an optically active material, the substance to be sensed can change a property of electromagnetic radiation coming from the second subregion and the semiconductor sensor device is formed such that the electromagnetic radiation of which the property has been changed can reach a detector. The present invention is based on the following recognitions. Firstly, the invention is based on the recognition that the surface of the first and third region comprising an optically inactive semiconductor material like a IV element and the surface of the second subregion comprising an optically active semiconductor material like a III-V material, have a different surface chemistry. The latter includes a possible surface reconstruction and/or the involvement of oxygen atoms that may be present as a native oxide, e.g. on the surface of silicon. Such a different surface chemistry is particularly suitable for increasing the sensitivity of a sensor device according to the invention. In this way, a substance to be detected can more readily stick to the free outer surface of the III-V subregion than to the free outer surface of the IV-element subregion. In this way the sensitivity of the sensor can be increased. The latter may be effected by the native outer surfaces of the subregions themselves but said surfaces can also be treated differently using said different surface chemistry in order to increase the sensitivity. Thus, the surface of the IV element subregion may be treated such that its sticking capability is decreased and/or the surface of the III- V compound subregion may be treated such that its sticking capability is increased. Secondly, the invention is based on the recognition that the use of a second subregion comprising an optically active semiconductor material, like a III-V material, allows for an optical detection of the substance to be detected in a simple manner since a property of electro-magnetic radiation coming from said optically active second subregion will be changed if said substance is adsorbed to the surface of said second subregion. Said property may be in particular the intensity or the wavelength of said electro -magnetic radiation but a change in other properties like the polarization could be used for the purpose of detecting the substance. Electro-magnetic radiation coming from said second subregion can be generated in several manners. If the mesa-shaped semiconductor region comprises a pn-junction in or close to the second subregion and its ends are connected to electrical connection regions, said radiation may be generated like in a laser or LED (= Light Emitting Diode) device by making an electric current flow between said electrical connection regions.

According to the invention the sensor device is formed such that such radiation of which a property has been changed by the substance to be detected can reach a detector. This can be realized e.g. by integrating a detector into the sensor device close to the mesa-shaped semiconductor region. Such a detector may be e.g. a pn-diode functioning as a photodiode with which e.g. the intensity of the radiation can be measure or a CCD (= Charge Coupled Device) image sensor.

Another attractive way of using a semiconductor sensor device according to the invention is to use an external radiation source, e.g. a laser or a LED of which the emitted radiation is directed towards the second subregion. In particular in case of such an external radiation source, the sensor device should be formed such that said radiation can reach the second subregion. This can be realized if the mesa- shaped semiconductor region is freely admissible (e.g. open) at the side where the radiation source is positioned. If the semiconductor sensor device forms a closed space in which the mesa-shaped semiconductor region is locked, this can be obtained by closing the sensor device at the side where the radiation source is to be positioned by means of a radiation transparent substrate. In the latter case, also the detector of the electromagnetic radiation after its property has been changed can be positioned outside the sensor device at the side where the latter is open or provided with the transparent substrate. In a preferred embodiment the second subregion forms a quantum dot. By limiting the thickness of the optical second subregion between the two passive other subregions, the wavelength of emission/absorption of the second subregion can be adjusted. Moreover, in this way the sensitivity of the sensor can be increased. By choosing also the lateral dimensions of the mesa- shaped semiconductor region in the sub 100 nm domain, a quantum dot is formed with optimal properties.

In a further embodiment the first and third subregions comprise a IV element, preferably silicon or germanium or a mixed crystal of these elements, and the second subregion comprises a III-V compound. In this way, on the one hand the manufacturing technology is most compatible with today's advanced silicon technology while on the other hand the optical properties of the second subregion can be most easily used for sensing the substance since many III-V compounds (and II-VI compounds) have the desired properties, e.g. a direct bandgap structure.

Preferably, the III-V compound has an effective bandgap in the visible part of the spectrum. Taking into account the bandgap increase caused by using a quantum dot for the second subregion, suitable materials for the second subregion may be a material having a bandgap which is just outside the visible spectrum a the IR side thereof. Examples of suitable materials are GaP, GaAs or InP and more preferably materials having a lower (bulk) bandgap like InAs and mixed crystals like InGaAs or InAsP. Mixed crystals offer the additional advantage that the structure of the semiconductor region can be made such that the strain induced in case of passive regions of silicon is made minimal.

In another favorable embodiment of a semiconductor sensor device according the invention the device comprises a mesa-shaped semiconductor region with between optically inactive other subregions a further optical active subregion with different optically properties than the second subregion such that two different substances can be detected by the sensor device. E.g. a double dot device where the dots have different bandgap energies allows for multiplexed detection. In one modification, the two different quantum dots are present in one single mesa-shaped semiconductor region. However, forming different quantum dots in different mesa-shaped semiconductor regions forms another attractive modification.

In an another embodiment the mesa-shaped semiconductor region is connected at a first end to a first electrically conducting connection region and at a second end to a second electrically conducting connection region. In combination with a pn-junction being present in the mesa-shaped semiconductor region, this allows for an internal source of radiation in the sensor device. Optical properties of the radiation emitted can be changed by the substance after it has been adsorbed to a free surface of the second subregion, e.g. the wavelength or intensity of such radiation.

In case the first and third subregions comprise a group IV element of the periodic system like silicon, the latter may be advantageously partly or completely oxidized, to form a SiO₂ barrier. In this way the leakage of charges from the second subregion, e.g. created by the adsorption of the substance to be detected can be prevented.

In yet another modification a free outer surface of the second subregion is functionalized so as to increase the probability that the substance to be detected sticks to said free outer surface. In this way the sensitivity of the sensor can be increased. Such an increase of the sensitivity can also be obtained by functionalizing a free outer surface of the first and third subregions so as to decrease the probability that the substance to be detected sticks to said free outer surface.

Preferably, the mesa-shaped semiconductor region comprises a nano-wire and preferably the device comprises a plurality of mutually parallel nano-wires. In this way a very high sensitivity and/or the use of multiplexing is possible. At the same time the manufacturing can be relatively simple, e.g. by using the VLS (= Vapor Liquid Solid) epitaxy technique. If the latter is used a plurality of nano-wires can be easily obtained while they are positioned on the surface of the semiconductor body with their length direction running perpendicular to said surface.

The semiconductor device according to the invention is preferably suitable for detecting a bio molecule such as a protein binding to an antibody. An antibody that is specific for the protein in question can be attached to a free surface of the second subregion before the fluid containing the substance to be detected passes along said second subregion. The invention further comprises a diagnostic instrument comprising a semiconductor sensor device according to the invention. Such instrument may comprise further a source for electro -magnetic radiation used in detecting the substance to be detected and a detector for detecting the electro -magnetic radiation after one of its properties has been changed by the substance to be detected. Since such a source and detector can be solid-state compounds, the instrument can be relatively compact and cheap. The semiconductor part may be insertably connected to the instrument such that it can be easily replaced with a new or other semiconductor sensor device e.g. after failure of the original semiconductor sensor device or in case multiplexing is desired in order to detect different substances. A method of manufacturing a semiconductor sensor device for sensing a substance comprising a mesa-shaped semiconductor region which is formed at a surface of a semiconductor body, while a fluid comprising a substance to be sensed can flow along the mesa-shaped semiconductor region, wherein the mesa-shaped semiconductor region is formed with viewed in a longitudinal direction subsequently a first semiconductor subregion comprising a first semiconductor material and a second semiconductor subregion comprising a second semiconductor material different from the first semiconductor material, is according to the invention characterized in that the first and third semiconductor material are formed of an optically passive material and the second semiconductor material is formed of an optically active material, the substance to be sensed can change a property of electromagnetic radiation coming from the second subregion and the semiconductor sensor device is formed such that the electromagnetic radiation of which the property has been changed can reach a detector.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, to be read in conjunction with the drawing, in which

Fig. 1 shows a cross-section perpendicular to the thickness direction of a first embodiment of a semiconductor sensor device according to the invention, Fig. 2 shows a perspective view of a second embodiment of a semiconductor sensor device according to the invention,

Fig. 3 shows a perspective view of a third embodiment of a semiconductor sensor device according to the invention,

Fig. 4 shows a perspective view of a fourth embodiment of a semiconductor sensor device according to the invention and

The Figures are diagrammatic and not drawn to scale, the dimensions in the thickness direction being particularly exaggerated for greater clarity. Corresponding parts are generally given the same reference numerals and the same hatching in the various Figures.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a cross-section perpendicular to the thickness direction of a first embodiment of a semiconductor sensor device according to the invention. The device 10 comprises in this example a silicon substrate 15 that is provided with a silicon dioxide layer 16. Thereon a nano-wire 11 is positioned with its length direction parallel to the surface of the semiconductor body 12. The nano-wire 11 comprises three sections 1,2,3 with different compositions. A first section 1 comprises lowly doped p-type silicon forming, a second section 2 comprising a quantum dot region 2 comprising GaAs and a third section 3 comprising again silicon but now of the p-type conductivity. These sections 2,3 are provided with (semi)conducting regions 13,14 of respectively highly p-type doped and highly n-type doped poly crystalline silicon forming the electrical connection regions of a radiation emitting diode formed within the nano-wire 11. An antibody 80 coupled to a protein 30 signaling a certain disease and flowing in a blood sample 20 along the nano-wire 11 will after landing on and sticking to the GaAs region 1 induce a charge into the channel region of the radiation - emitting diode. Said charge increases a large change in the optical properties of in particular the central section 2 of the diode, which can be signaled by a detector 50. Said property of the radiation E coming from the radiation-emitting subregion 2 can be e.g. the emission wavelength or the intensity. Both can be signalized by a different/changing response from the detector 50. The latter may be e.g. a (silicon) photodiode or a CCD image sensor. In this example the relevant radiation E is obtained by emission induced by an electrical current through the nano-wire 11.

However, an attractive alternative is formed by using an external source 40 for radiation R that is directed towards the surface of subregion 2. Such external source 40 can be a radiation-emitting source like a LED (= Light Emitting Diode) or a LASER (= Light Amplification by Stimulated Emission of Radiation). After being absorbed by optical active subregion 2, a property like intensity or wavelength can be changed by the presence of a substance 30 to be detected which is present on the surface of subregion 2.

The devices 10 of this example may be manufactured by positioning nano- wire(s) 11 obtained by VLS (= Vapor Liquid Solid) epitaxy on the surface of the desired substrate. Subsequently, a part of the nano-wire 11 is masked and polycrystalline regions 13,14 are formed by deposition and patterning. Hereinafter the mask used on the nano-wire 11 is again removed. Another way of manufacturing such a sensor device is by using (selective) epitaxial processes to form the various subregions followed by photolithography and etching to form the mesa / nanowire. Fig. 2 shows a perspective view of a second embodiment of a semiconductor sensor device according to the invention. In this example the nanowire 11 is the same as in the previous example but it does not contain any doping, i.e. no intentionally doped regions. Moreover, a second nanowire 11' comprises in its second subregion 2', a different optical active material, e.g. InAs. In this way the device 10 can be sensitive to two different substances 30. Of both types of nano wires 11,11' a plurality is present on the surface of a substrate 15 which in this example comprises a quartz or glass substrate 15. The nanowires 11,11 ' are sticked to the surface of the substrate 15 by an optically passive and transparent glue. Below the substrate 15 a detector 50 is present which in this example comprises a CCD image sensor. Above the substrate 15 a radiation-emitting source 40 is present to provide for radiation, which is directed towards subregions 2,2' of nanowires 11,11'. The nanowires 11,11' may be formed in the same as indicated in the previous example.

The three components 15, 40,50 of the device 10 of this example are attached to a housing, which is not shown in the drawing. The substrate 15 can be releasably attached into said housing in order to be replaced in case of failure or if a different sensor device is desired for detecting other substances.

Fig. 3 shows a perspective view of a third embodiment of a semiconductor sensor device according to the invention. The sensor device 10 of this example comprises a plurality of nano-wires 11,11' which are grown by the above mentioned VLS epitaxy technique on an SOI substrate as the substrate used in the first example. In order to obtain different nanowires 11,11' two different growth cycles can be used, the spots for nanowires 11 ' being masked during the growth of nanowires 11 and the nanowires 11 being masked during growth of the nanowires 11'. After the growth has been completed the silicon part below the BOX layer is removed using a substrate transfer technique resulting in a substrate 25 comprising again a transparent substrate like quartz or glass. The thin silicon layer above the BOX layer may be selectively removed or either be so thin that it transmits most of the radiation E coming from the second subregion 2,2' of the nanowires 11,11'. In this way, again a detector 50 can be positioned above the semiconductor body 12 while a radiation-emitting source 40 is positioned above the latter. Fig. 4 shows a perspective view of a fourth embodiment of a semiconductor sensor device according to the invention. The sensor device 10 of this example is similar to the third example. The difference being as follows: the nanowires 11,11' are grown on a silicon substrate 15 that it is highly doped and forms an electrical connection region 13 contacting the nanowires 11,11' which are provided with a radiation-emitting pn-junction as in the first example. The free end of the pluralities of nanowires 11,11' are attached on their other end with a further substrate 17 comprising glass or quartz which is covered by a transparent electrically conducting layer like an Indium-Tin oxide. In this way, the substrate 17 forms another electrical connection region 14 for the pn-diodes formed in the nanowires 11,11'. The transparent substrate 17 allows again that a detector 50 is positioned at that side of the sensor device 10.

For all examples it is to be noted that the sensitivity of a sensor device according to the invention can be increased by a surface modification of the second subregion 2 which results in an increased sticking probability of the substance 30 to be detected on the surface of the second subregion 2. Similarly, the sensitivity of a sensor device according to the invention can be increased by a surface modification of the first and third subregions 1,3 which results in an decreased sticking probability of the substance 30 to be detected on the surface of said subregions 1,3. Both surface treatments can also be combined to increase the sensitivity.

It will be obvious that the invention is not limited to the examples described herein, and that within the scope of the invention many variations and modifications are possible to those skilled in the art.

For example it is to be noted that instead of antibodies also ssDNA (= Single Strand Desoxyribo Nucleic Acid) molecules may advantageously be attached to a surface of the first subregion provided with a monolayer of a suitable compound to enhance selective attachment. A specific complimentary DNA chain that is to be detected, can selectively be bonded to said ssDNA. As in the case of a protein binding to an antibody, the binding of said complimentary DNA to the ssDNA will result in charge redistribution near the surface of the sensor device that then will be detected with high sensitivity.

Furthermore it is noted that various modifications are possible with respect to individual manufacturing steps. For example other deposition techniques can be selected instead of those used in the example.

Also other optical active materials can be used such as II-VI semiconductor materials like e.g. ZnS, ZnSe or ZnTe. It is further to be noted that the effective bandgap of the optical active material can also be in the UV (= Ultra Violet) or IR (= InfraRed) part of the spectrum.

Claims

CLAIMS:

1. Semiconductor sensor device (10) for sensing a substance (30) comprising a mesa- shaped semiconductor region (11,11') which is formed on a surface of a semiconductor body (12) while a fluid (20) comprising the substance (30) to be sensed can flow along the mesa-shaped semiconductor region (11), wherein the mesa- shaped semiconductor region (11) comprises, viewed in a longitudinal direction, subsequently a first semiconductor subregion (1) comprising a first semiconductor material, a second semiconductor subregion (2) comprising a second semiconductor material different from the first semiconductor material and a third subregion (3) comprising a third semiconductor material different from the second semiconductor material, characterized in that the first and third semiconductor material comprise an optically passive material and the second semiconductor material comprises an optically active material, the substance (30) to be sensed can change a property of electromagnetic radiation (E) coming from the second subregion (2) and the semiconductor sensor device (10) is formed such that the electromagnetic radiation (E) of which the property has been changed can reach a detector (50).

2. Semiconductor sensor device (10) according to claim 1, characterized in that the second subregion (2) forms a quantum dot.

3. Semiconductor sensor device (10) according to claim 1 or 2, characterized in that first and third subregions (1,3) comprise a group IV element of the periodic system, preferably silicon or germanium or a mixed crystal of these elements, and the second subregion (2) comprises a III-V compound.

4. Semiconductor sensor device (10) according to claim 3, characterized in that the III-V compound has an effective bandgap in the visible part of the spectrum.

5. Semiconductor sensor device (10) according to claim 4, characterized in that the sensor device (10) comprises a mesa-shaped semiconductor (11,11') region with between optically inactive other subregions a further optical active subregion with different optically properties than the second subregion such that two different substances (30) can be detected by the sensor device (10).

6. Semiconductor sensor device (10) according to any of the preceding claims, characterized in that the mesa- shaped semiconductor region (11) comprises a pn-junction close to the second subregion (2) and is connected at a first end to a first electrically conducting connection region (13) and at a second end to a second electrically conducting connection region (14).

7. Semiconductor sensor device according to claim 3, 4 or 5, characterized in that the group IV element material of the first and third semiconductor regions (1,3) is selectively oxidized to form optically passive material comprising a group IV element oxide.

8. Semiconductor sensor device (10) according to any of the preceding claims, characterized in that a free outer surface of the second subregion (2) is functionalized so as to increase the probability that the substance (30) to be detected sticks to said free outer surface.

9. Semiconductor sensor device (10) according to any of the preceding claims, characterized in that a free outer surface of the first and third subregions (1,3) is functionalized so as to decrease the probability that the substance (30) to be detected sticks to said free outer surface.

10. Semiconductor sensor device (10) according to any of the preceding claims, characterized in that the mesa-shaped semiconductor region (11) comprises a nano-wire (11), preferably a plurality of mutually parallel nano-wires (11,11').

11. Semiconductor sensor device (10) according to claim 10, characterized in that the nano-wire(s) (11,11') are positioned on the surface of the semiconductor body (12) with their length direction running perpendicular to said surface.

12. Semiconductor sensor device (10) according to any of the preceding claims, characterized in that the device (10) is suitable for detecting a bio molecule such as a protein binding to an antibody.

13. Diagnostic instrument comprising a semiconductor sensor device (10) according to any of the preceding claims.

14. Diagnostic instrument according to claim 13, characterized in that the instrument comprises a source (40) for directing electromagnetic radiation to the second subregion (2) and a detector (50) for detecting electromagnetic radiation coming from the second subregion (2).

15. Method of manufacturing a semiconductor sensor device (10) for sensing a substance (30) comprising at least one mesa- shaped semiconductor region (11,11') which is formed at a surface of a semiconductor body (12), while a fluid (20) comprising a substance (30) to be sensed can flow along the mesa-shaped semiconductor region (11), wherein the mesa- shaped semiconductor region (11) is formed with, viewed in a longitudinal direction, subsequently a first semiconductor subregion (1) comprising a first semiconductor material and a second semiconductor subregion (2) comprising a second semiconductor material different from the first semiconductor material, characterized in that the first and third semiconductor material are formed of an optically passive material and the second semiconductor material is formed of an optically active material, the substance (30) to be sensed can change a property of electromagnetic radiation (E) coming from the second subregion (2) and the semiconductor sensor device (10) is formed such that the electromagnetic radiation (E) of which the property has been changed can reach a detector (50).