In preferred embodiments, the base plate may be formed by a substantially homogeneous planar body. Likewise, it may be preferred that the base plate is not a homogeneous body, but may have interruptions, for example in the form of slots, openings or other topologies. The base plate may also be formed, for example, by a lattice structure that deforms in a characteristic (measurable) manner when a load is exerted on the force conductor. The term ‘base structure’ can therefore preferably be used synonymously with the term base plate.

In a preferred embodiment, the base plate has a thickness between 0.1 mm and 2 mm, preferably between 0.3 mm and 0.7 mm.

In a preferred embodiment, the base plate and/or the force conductor is formed from a metal preferably selected from the group consisting of iron, steel, stainless steel, spring steel, brass, copper, titanium, aluminum, lead, magnesium, beryllium copper and/or other alloys of the foregoing.

In further preferred embodiments, the base plate and/or the force conductor can be provided not only from metals but also from other materials of microsystems technology, such as semiconductors, ceramics or plastics.

Ceramic materials in particular are characterized by high resistance to high-temperature applications or harsh environmental conditions, especially for the provision of base plates and/or force conductors. For example, the apparatus is also suitable for media separation due to the attachment of the sensor chip on the rear side of the base plate. Thus, for application in a flow sensor, the force conductor can be located in a flowing fluid (liquid or gas), while the sensor chip is installed on the opposite side of the base plate.

In a preferred embodiment, the base plate and/or force conductor may be formed from a substrate, preferably selected from the group consisting of monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide, and glass.

These materials are easy and inexpensive to process in semiconductor and/or microsystem manufacturing and are suitable for large-scale production. In addition, this allows the possibility to provide the apparatus comprising spring body and sensor chip preferably in an integrated (semiconductor) process. This simplifies production such that a particularly compact multi-axis force sensor can be provided at low cost.

The aforementioned dimensioning and materials of the force conductor and base plate have proven to be advantageous in providing a particularly sensitive measuring apparatus.

In a preferred embodiment, the base plate and/or the force conductor has a relief groove, preferably in the form of a border around the area on which the force conductor is affixed to the base plate. A relief groove designates in particular a recess, cavity or notch which is present in the form of a border on the base plate and/or the force conductor.

Particularly advantageous in this respect is the provision of a central bore within the pin and/or a relief groove, preferably in the form of a border around the area on which the force conductor is affixed to the base plate.

Both features, independently of each other, but particularly distinctly in combination, lead to characteristic deformations of the base plate in the fixing area, which allow particularly sensitive measurements of multiaxial loads on the force conductor.

In preferred embodiments, the spring body can be monolithic. That is, the force conductor, preferably a pin, and the base plate are formed from one block of material. However, the spring body can also be formed as a composite body, in which case the force conductor, preferably a pin, is fixed to the base plate.

Within the meaning of the invention, a sensor chip preferably means a semiconductor component comprising at least one substrate with one or more sensor elements and preferably an electronic circuit.

In a preferred embodiment, the one or more sensor elements are configured for resistive, preferably piezoresistive, optical, magnetic, inductive, and/or capacitive measurement of deformations, stresses, forces, and/or torques of the substrate.

Resistive and piezoresistive sensor elements are usually based on a change in electrical resistance due to a change in length of the substrate on which they are mounted. The piezoresistive change in resistance due to a strain on the sensor elements is significantly stronger (k-factor), especially in the case of (doped) semiconductors, and preferably allows more sensitive and accurate strain measurements. A change in resistance can preferably be measured by a change in the stress applied to the sensor element in a Wheatstone bridge.

Piezoelectric sensor elements are preferably based on the generation of an electrical voltage inherent to the material by means of compressive and/or tensile forces acting on the arrangement.

An inductive measurement arrangement is preferably based on the strength of the current induced by a varying magnetic field.

An optical sensor element can preferably measure strain between different areas via a distance measurement (e.g. interferometric measurement) in which the superimposition of coherent optical signals provides information that can be read out regarding their phase difference. This phase difference in turn preferably contains information about the distance between the areas.

A magnetic sensor element can, for example, be based on a Hall sensor which generates a different voltage depending on the position within a magnetic field and thus depending on the experienced magnetic flux density. Thus, preferably with a fixed reference magnetic field, the measured voltage can be used to detect the relative position of the Hall sensor to this magnetic field. This measurement principle can be used in particular to realize a distance measurement (and thus stress or strain measurement) between different areas on the substrate.

A capacitive sensor element is preferably based on the principle of a measurable change in the capacitance of a capacitor with a variation in the distance between the capacitor plates (electrodes). A variety of different implementations are conceivable, for example in the form of capacitor plates on the substrate, as (MEMS) comb structures, in which the comb coverage and/or the comb spacing can be varied depending on the embodiment.

A person skilled in the art knows various sensor elements as well as materials which can preferably be used to enable resistive, preferably piezoresistive, optical, magnetic, inductive and/or capacitive measurement of deformations, stresses, forces and/or torques.

Preferably MEMS sensors are used, i.e. a component based on MEMS technology. MEMS stands for the English term microelectromechanical system, i.e. a microsystem, whereby a compact design (in the range of micrometers) is achieved with simultaneously excellent functionality with ever lower manufacturing costs. In particular, the entire sensor chip comprising the sensor elements and the electronics is preferably fully integrated into CMOS technology.

Preferably, the sensor elements are arranged on a substrate together with an electronic circuit for evaluating and/or controlling the sensor elements and are in contact with this circuit via electrical connections, which are made, for example, by wire bonding and/or are laid out in the substrate, e.g. by conductor tracks. The substrate functions in particular as a mechanical carrier, but can also realize electrical functions, e.g. providing electrical connections for the individual components.

Preferred electronic circuits comprise, but are not limited to, an integrated circuit (IC), an application-specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), a microprocessor, a microcomputer, a programmable logic controller, and/or other electronic, preferably programmable, circuitry.

By means of an electronic circuit and/or further electronic components on the sensor chip, it is preferably already possible to read out and/or (pre-)process the measured data of the sensor elements. For this purpose, a multiplexer (MUX, for reading out the signals of multiple sensor elements), an operational amplifier (e.g. differential difference amplifier (DDA) with variable gain) or analog-to-digital converter (ADC) can be present on the sensor chip or a circuit carrier for converting the signals into digital data.

In a particularly preferred embodiment, the one or more sensor elements comprise piezoresistive structures, preferably piezoresistive sensor bridges.

Preferably, the piezoresistive sensor bridges can be designed as Wheatstone bridges, preferably as full bridges. Advantageously, four piezoresistive structures forming the full bridge can be positioned very close to each other. Sources of interference such as temperature drift are compensated for, since the temperature drift preferably affects all piezoresistive structures equally.

Particularly preferably, the sensor chip comprises more than 3, 5, 10, 15, 20 or more sensor elements, wherein the sensor elements are distributed at various positions on the substrate.

Due to the large number of sensor elements, a particularly precise measurement of a two-dimensional distribution of deformations, stresses, forces and/or torques on the substrate can be carried out. Unlike semiconductor strain gauge sensors, for example, the sensor chip does not integrate the local load on the substrate over its entire surface, but enables a spatially resolved measurement of the stress or strain in the relevant area below the base surface by means of the large number of sensor elements on the substrate.

In a preferred embodiment, one or more of the sensing elements is used to measure differential stress σ_xx−σ_yy—on the substrate. The stresses σ_xxand σ_yycorrespond to orthogonal normal stresses in the xy-plane.

In a preferred embodiment, one or more sensor elements measure a shear stress σ_xyso that shear forces acting on the substrate can also be detected.

In a preferred embodiment, the sensor elements are designed as piezoresistive sensor bridges, which are arranged in a square as Wheatstone bridges, whereby a shear stress is detected by n-channel-based transistors and whereby the sensor bridge is rotated by 45° to an (x,y) coordinate system, while p-channel-based transistors are arranged as a sensor bridge parallel to the coordinate system and measure the normal differential stress.

Particularly preferably, the piezoresistive sensor bridges are designed as square field-effect transistors (FET, preferably MOSFET) with four source/drain contacts (piezo FETs) that exploit the piezoresistive shear effect in n-type (NMOS) or p-type (PMOS) inversion layers. Preferably, NMOS sensor elements are used for measuring the shear stress σ_xyand PMOS sensor elements are used for measuring the normal differential stress (σ_xx−σ_yy). Examples of preferred sensor chips with piezoresistive sensor bridges as sensor elements are disclosed in Gieschke et al. 2009 and Kuhl et al. 2013, among others. Advantageously, particularly compact sensor elements can be realized with dimensions of 10 μm×10 μm or smaller.

Particularly preferably, there can be multiple sensor elements on the sensor which detect a differential stress of the normal stresses σ_xx−σ_yyas well as multiple sensor elements which detect a shear stress σ_xy. This provides a particularly precise image of a two-dimensional stress distribution in the substrate and thus indirectly of the area of the base plate on which the force conductor is fixed.

In a preferred embodiment, the substrate of the sensor chip comprises a semiconductor material, preferably silicon, monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride and/or indium phosphide. These materials are easy and inexpensive to process in semiconductor and/or microsystem production and are also well suited for bulk production. Likewise, these materials are particularly suitable for doping and/or coating to achieve the desired electrical, mechanical thermal and/or optical properties in specific areas.

The sensor elements for measuring a mechanical deformation and/or stress acting on the sensor chip are integrated onto or into the substrate. Materials and/or production techniques known from the semiconductor industry can be used here, which are characterized by their efficiency, simplicity, low production costs and suitability for the production of large quantities.

For example, masking (preferably photolithography) on the substrate can be used to define areas for forming the sensor elements and/or an electronic circuit, on which further semiconductor processes such as etching, doping and/or deposition can be carried out. The substrate can also be a multilayer substrate comprising two or more layers which are individually processed and joined together (bonding).

An etching and/or patterning can preferably be selected from the group comprising dry etching, wet chemical etching and/or plasma etching, in particular reactive ion etching, deep reactive ion etching (Bosch process).

An application or deposition can preferably be selected from the group comprising physical vapor deposition (PVD), in particular thermal evaporation, laser beam evaporation, arc evaporation, molecular beam epitaxy, sputtering, chemical vapor deposition (CVD) and/or atomic layer deposition (ALD).

Doping can be performed, for example, by known processes such as alloying, diffusion, and/or ion implantation.

In a preferred embodiment, the substrate of the sensor chip has a thickness between 100 μm and 600 μm, preferably 200 μm and 400 μm. The dimensioning of the substrate is particularly suitable for ensuring a good transfer function between deformations from stresses or deformations of the area of the base plate and the sensor elements.

Preferably, the sensor chip is attached to the rear of the base plate on one side of the substrate. For this purpose, for example, an adhesive can be used which creates a direct connection between the substrate and the base plate.

In addition to the connection by means of an adhesive, a variety of techniques from integrated circuit packaging technology (ICP) can be used for a mechanical coupling of the sensor chip to the base plate. These include without limitation the use of an adhesive film, soldering, brazing (welding), reactive joining (preferably with thermally reactive films, in particular nanometer multilayers or reactive multilayer systems RMS joining) or also bonding, for example anodic bonding, direct bonding, bonding processes with intermediate layers (e.g. eutectic bonding), glass frit bonding, adhesive bonding and/or selective bonding.

Mechanical deformations are preferably transferred directly to the thin-film substrate via mechanical coupling using ICP technology (for example, adhesive bonding, soldering, reactive joining, bonding, etc.), with the sensor elements on the opposite side of the substrate picking up a two-dimensional stress or deformation image.

The sensor elements are therefore preferably used to detect deformations or stresses of the sensor chip itself or of the substrate. Due to the mechanical coupling with the force conductor, the measured data provide direct conclusions about stresses, forces, deformations or torques that act on the force conductor or on the object in which the force conductor is integrated.

By means of various calibrations, it is possible to obtain not only relative information about the changes in the mechanical loads in the force conductor or object, but also absolute information about the stresses, forces, deformations or torques acting in the component. For example, mechanical properties of the sensor chip or the substrate as well as of the force conductor can be included in the calibration.

Due to the finite thickness of the substrate, the two-dimensional stress or deformation image produced by the sensor elements on the free side of the substrate may differ from the actual stress or deformation distribution on the base plate. However, the differences are constant for a given sensor chip and substrate, so these are included in a calibration.

In another preferred embodiment, the apparatus comprises one or more inductive interfaces, preferably coils, for a transmission of measured values and/or for the supply of energy.

Such a telemetric interface allows a particularly flexible use of an energy-autonomous apparatus.

Via the inductive interface, the electrical power required for operation can be coupled in by an external reader. The integrated sensor elements can then measure the stress or deformation distribution and then transmit the measured data wirelessly to the reader. For data transmission by means of the telemetric interface, it may also be preferable, for example, to use NFC (near field communication) standard.

Advantageously, the apparatus can also be used, for example, to monitor rotating objects, such as tool spindles, which is otherwise not easily possible by means of cable-based contacting.

The inductive interface or (transponder) coils can be installed on the sensor chip itself, or separately, for example on a printed circuit board.

In a preferred embodiment, the sensor chip is in contact with a circuit carrier. A circuit carrier is preferably a component comprising an electrically insulating material on which electrically conductive connections (conductor tracks) and/or electronic components or assemblies are present.

In preferred embodiments, the circuit carrier is a printed circuit board, whereby both conventional (rigid) printed circuit boards and flexible printed circuits can be used.

In a preferred embodiment, the sensor chip can also be in contact with a circuit carrier by means of a chip-on-board method, with electrical contact preferably being made by means of a flip-chip assembly or chip-and-wire technique, preferably by means of wire bonding.

In chip-and-wire technology, the sensor chip is preferably bonded directly to the circuit carrier (e.g. a printed circuit board) and electrically connected to the circuit carrier by means of wire bonding (bridges made of fine wire).

Preferably, for example, the sensor chip can be attached to the rear of the base plate by means of ICP technology (for example, adhesive bonding, soldering, reactive joining, etc.) and connected via an electrical connection, for example a wire bond, to a printed circuit board that is also attached to the base plate. Alternatively, a flip-chip assembly can also preferably be used, in which case the sensor chip is preferably attached to the circuit carrier (e.g. printed circuit board) with an active contacting side on which the sensor technology (sensor elements) and/or electronics are located. The contacting is preferably carried out by means of contacting bumps, for example by means of an anisotropic conductive film. In flip-chip assembly, too, it is preferred to attach the sensor chip directly to the base surface by means of an adhesive for the best possible force transfer with the substrate, with the printed circuit board on the accessible side facing away from the base plate.

Contact can be established between the sensor chip and an external data processing unit in a wired or wireless manner, preferably via an interface on the circuit carrier.

Contact can be established between the sensor chip and an external data processing unit in a wired or wireless manner, preferably via an interface on the circuit carrier (e.g. a printed circuit board).

Different shapes may be preferred for the sensor chip, for example a circular shape, rectangular shape or other polygonal shape, the shape of a rectangle, especially a square, is particularly preferred.

In a preferred embodiment, the sensor chip has a width and/or length between 0.5 mm and 10 mm, preferably 1 mm and 5 mm, preferably 1 mm to 3 mm. The thickness of the sensor chip is preferably less than 1 mm, preferably less than 700 μm, or less than 500 μm.

Thus, in the preferred embodiment, the sensor chip is substantially flat, i.e., the sensor chip is characterized by a greater width and/or length in one plane (xy-plane) compared to a dimension orthogonal thereto (z-axis, thickness). The factor may be, for example, 2, 3, 5 or more.

In a preferred embodiment, the sensor chip has an area from 0.25 mm²to 100 mm², preferably 1 mm²to 25 mm², more preferably 1 mm²to 9 mm².

In another aspect, the invention preferably relates to a system comprising.

- a) a described apparatus and
- b) a data processing unit
  
  wherein the data processing unit is configured for reading out measured data detected by the sensor chip.

The average person skilled in the art will recognize that technical features, definitions and advantages of preferred embodiments disclosed for the apparatus according to the invention apply equally to the system comprising such apparatus, and vice versa.

Preferably, the data processing unit is configured to detect the forces and/or torques acting on the force conductor by means of the measured data relating to deformations, stresses, forces and/or torques of the substrate detected by the sensor chip.

The data processing unit thus preferably permits evaluation of the measured data from the sensor chip in order to detect the actual loads on the force conductor or an object connected to it.

The electronic circuit on the sensor chip itself can also already perform a (pre-)evaluation of the measured data. However, it may also be preferred that the electronic circuit essentially forwards the measured data unprocessed to the (external) data processing unit for further processing and/or evaluation.

The (external) data processing unit is preferably a unit which is suitable and configured for receiving, transmitting, storing and/or processing data, preferably measured data. The data processing unit preferably comprises an integrated circuit, a processor, a processor chip, microprocessor or microcontroller for processing data, as well as a data memory, for example a hard disk, a random access memory (RAM), a read-only memory (ROM) or also a flash memory for storing the data.