Patent Application: US-37683307-A

Abstract:
a miniature sensor for detecting acceleration and deceleration processes has at least one bar - like spring element which is formed by a nanowire , which is connected by one end to the detector substrate and projects from the latter and which preferably carries at its free end a coating emitting a permanent magnetic stray field , or a nanoparticle of this type , wherein the nanowire and magnetic stray field coating , or mass , together form the inertial mass . a magnetic field detection layer composed , for example , of magnetoresistive material , is disposed at least in the region near the connected end of the nanowire . the substrate is preferably provided with such a layer which preferably , for its part , as sensor component forms a constituent part of a magnetic field detection unit .

Description:
fig1 a to 1 c show three signal - generating acceleration sensors of simple design in accordance with the invention , said sensors being different but of substantially the same type , and moreover illustrate in a simple manner the underlying sensor principle of the interaction of magnetic components with the detector layer via magnetic stray fields ; fig2 a to 2 e show various arrangements of single crystals or nanowires with magnetic nanoparticles and magnetic field detection layer relative to one another ; and fig3 a to 3 c show more complicated embodiments of sensors of the novel type that are sensitive to one -, two - and three - dimensional acceleration and deceleration processes . the essential components of the invention and the principle underlying the invention are illustrated schematically in fig1 a to 1 d . a nanowire 2 functions as a flexible spring which can bend under the load of the inertial mass of nanowire 2 and magnetic nanoparticle 3 coupled thereto . in this case , the magnetic nanoparticle 3 is expediently fixed to the upper , free end 22 of the nanowire 2 , but can also be fixed at any other position along the nanowire 2 . the nanowire 2 and the magnetic particle 3 together form the inertial mass tm . the change in the position of the inertial mass tm is detected by means of a magnetic stray field mf emitted by it . said stray field is generated by magnetic materials used for the production of the nanowire 2 and / or of the nanoparticle 3 . the magnetic stray fields ms are detected by magnetoresistive detectors or by such a detector 4 which are or is situated in direct proximity to the nanowires 2 . said magnetoresistive detectors 4 are expediently produced by means of thin - film methods on the substrate 5 . if the position of the inertial mass tm , that is to say of the composite of nanowire 2 plus nanoparticle 3 , changes , the strength of the stray field signal in the detector 4 also changes . the intensity of the change depends on the relative movement direction of inertial mass tm and detector 4 . a change in distance along the direct connecting straight line generates the largest signal change and changes according to an exponential law with a power of between 2 and 3 . optimized design rules for the concrete construction of the novel sensor 1 can be derived from this . fig1 a shows how , from a detector substrate 5 which is coated with the magnetic field detection layer 4 and is concomitantly moved with an object , the single crystal or nanowire 2 , which is bound by an end 21 to the substrate 5 or to the detection layer 4 and grows therefrom obliquely upward , projects up at an acute angle α , said single crystal or nanowire carrying at its free end 22 the nanoparticle 3 generating the permanent magnetic stray field ms . upon the occurrence e . g . of an acceleration of the object and hence of the substrate 5 and of the detector layer 4 toward the left , the magnetic stray field ms of this system is displaced with slight curvature of the nanowire 2 toward the right and hence also movement of the magnetic nanoparticle 3 toward the right downward , and this small yet highly reproducible movement brings about in the magnetoresistive coating 4 a change in the electrical resistance thereof . this change in resistance is registered by the detection unit 7 and possibly amplified and finally forwarded to a storage , display and / or output unit 8 . the particular advantage of the novel acceleration sensors 1 is that they are present in extremely miniaturized form and can preferably indeed themselves be with their magnetoresistive layer 4 an integral part of detection electronics , in particular of a chip , which enables the nano - design thereof . fig1 b illustrates an acceleration sensor 1 with nanowire 2 with magnetic nanoparticle 3 , said nanowire growing obliquely from the substrate 5 and then curving upward toward the perpendicular , and represents its movement upon acceleration or deceleration by a double - headed arrow , from which relatively small signals should be expected upon acceleration , and in accordance with fig1 c a nanowire 2 growing steeply from the substrate 5 is provided , but said nanowire is curved downward toward the magnetoresistive layer 4 and can generate a relatively large or large signal upon acceleration . fig1 d shows an oblique single crystal or nanowire 2 without a separate mass at its end , although it is equipped there with a magnetic coating 3 ′. with reference symbol meanings otherwise remaining the same , fig2 a to 2 e show measurement principle and position on the basis of a nanowire 2 growing from the magnetic field coating 4 approximately “ centrally ” and at a right - angle , a nanowire 2 growing from said coating 4 in right - angled fashion at the edge thereof , and a nanowire 2 which likewise projects up in right - angle fashion and is surrounded by the magnetoresistive layer 4 with a spacing a being maintained , and furthermore a nanowire 2 which projects up from the substrate 5 at the acute angle α at a distance b alongside and finally in the magnetic field detection layer 4 . with reference symbol meanings otherwise remaining the same , fig3 a shows a substrate 5 configured with furrows 51 , for instance , wherein one flank 52 at the furrow 51 is coated with the magnetic field detection layer 4 , and the nanowire 2 with the nanoparticle 3 projects up from the other flank 52 , here without a detection layer ,— here perpendicularly and approximately parallel to the flank 51 —, whereby a highly sensitive , at least 1 - dimensional acceleration sensor 1 is provided . in the case of the sensor 1 in accordance with fig3 b , a plurality of upright nanowires 2 in a for example regular arrangement project up perpendicularly from the substrate 5 or from the magnetic field detection layer 4 thereof , whereby a very sensitive 2 - dimensional acceleration sensor is provided . in the case of the sensor 1 in accordance with fig3 c , the substrate 5 is embodied with a plurality of here e . g . three “ hills ” 55 arranged in linearly structured fashion , from the highest locations 551 of which a respective nanowire 2 projects away perpendicularly . in the case of the first hill 55 on the left , no further nanowire is provided ; in the case of the hill 55 in the center , both hill flanks 552 , 553 are embodied with nanowires 2 projecting up in each case perpendicularly therefrom ; and , finally , the right - hand hill 55 carries only a nanowire 2 with the nanoparticle 3 projecting up from said hill from a right - hand flank 553 . this sensor shown in fig3 c is suitable , in particular , for very effective detection and determination of acceleration and deceleration processes in all three spatial dimensions . fig1 and 2 thus demonstrate the effect of perpendicular and oblique nanowires 2 assuming that the detector 4 runs parallel to the surface of the substrate 5 as a thin layer . oblique nanowires 2 have an oscillation component perpendicular to the detector 4 , and thus generate a distinct change in the stray field components under an oscillation period . fig2 a to 2 e show a series of positioning possibilities for the nanowire 2 together with magnetic particle 3 relative to the detector 4 . the magnetic particle 3 can be composed of ferromagnetic or paramagnetic material . magnetized ferromagnetic nanoparticles 3 independently generate a magnetic stray field ms . an external constant and homogeneous magnetic field can be added in order to amplify said stray field . such a magnetic field is certainly favorable or necessary for paramagnetic or superparamagnetic particles . in accordance with the invention three preferred possibilities should be mentioned for fitting the magnetic nanoparticle 3 , where it should be emphasized that there are by all means further possibilities : the nanowire 2 is grown using a seed of ferromagnetic or paramagnetic material which is ultimately situated at the tip of the nanowire 2 and can itself generate a magnetic stray field ms . magnetic material can be fitted to the nanowire 2 subsequently and in a targeted manner by means of conventional lithography and coating processes . the disadvantage here consists in the additional process steps which become necessary . magnetic particles can be coupled via suitable binding sites to the nanowire or seed . this can occur in solution , for example : dissolved magnetic nanoparticles 3 having specific binding sites on the outer skin bind to the surfaces of the nanowire 2 or seed upon contact . a typical binding of the magnetic particle 3 would be for example via a thiol binding to a gold surface of the seed . the production of the magnetoresistive detectors on the substrate surface is preferably effected by means of the methods of layer production and lithography . in this case , relatively recent magnetoresistive effects such as , for example , giant magnetoresistance gmr and tunneling magnetoresistance tmr are preferred since they supply significantly higher signal amplitudes . different dimensionalities of the novel acceleration sensor 1 arise depending on the positioning and orientation of nanowires 2 and magnetoresistive detectors 4 . by skillfully setting the growth conditions of the nanowires 2 and the predetermined substrate topographies 5 , it is possible to produce both 1 - dimensional and 2 - and 3 - dimensionally sensitive acceleration sensors 1 . the combination of nanowires 2 and magnetic detection as provided in accordance with the present invention permits a unique access to these highly desirable sensor concepts . examples of embodiments of 1 -, 2 - and 3 - dimensional sensors 1 are illustrated in fig3 a to 3 c . the configuration in fig3 a shows an example of a possible arrangement for a 1 - dimensional sensor 1 . forces parallel to the nanowire 2 have no effect since the nanowire 2 is too stiff . forces parallel to the sensor layer 4 , that is to say in the plane of the paper , do not yield a signal change , since the stray field effect on the sensor 4 remains unchanged . only movement and forces perpendicular to the sensor layer 4 are detected with maximum signal amplitude . nanowires 2 projecting away perpendicularly from the detector layer 4 , as shown in fig3 b , can move in two dimensions . this means that only forces in a plane can be determined . such a sensor in accordance with fig3 b is isotropically two - dimensional . fig3 c shows one of the possible variants , specifically a very simple variant , of a 3 - dimensional sensor 1 . here all forces in all three spatial directions lead to a detector reaction . this sensor 1 is non - specific to the respective direction . however , any acceleration in an arbitrary direction finds a matching nanowire 2 which it can move vertically with respect to the sensor layer 4 and thus trigger a signal . as far as the advantages of the invention are concerned , the following should finally be noted in this respect : cost factor : the production of the novel acceleration sensors comprises simple process steps which are significantly more cost - effective in comparison with the production of traditional sensors of this type . consequently , the novel product has a crucial cost advantage . sensor variability : by simply changing the geometries of the nanowires , the properties of the sensors can be precisely adapted to the respective tasks and be set in a targeted manner without changing the production procedures . the basic layout remains unchanged . in particular , resonant frequencies and frequency responses can be preset , and can also be combined with one another . combination : the sensors according to the invention can be combined with other electronic or sensor - 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