WO2008089950A1

WO2008089950A1 - Mems sensor for in situ tem atomic force microscopy

Info

Publication number: WO2008089950A1
Application number: PCT/EP2008/000454
Authority: WO
Inventors: Alexandra Nafari; Krister Svensson; Håkan OLIN; Peter Enoksson; Cristina Rusu; David KARLÉN
Original assignee: Nanofactory Instruments Ab
Priority date: 2007-01-22
Filing date: 2008-01-22
Publication date: 2008-07-31

Abstract

A force sensor (200) for atomic force microscopy comprising a MBMS or NEMS produced force sensor with a cantilever with a piezo resistive layer on the cantilever (300), wherein the sensor further comprises contact areas (304), a dummy cantilever (301) with a resistive layer, and where the piezoresistive layers are connected to a Wheatstone bridge located on the sensor. The sensor is to be positioned in a TBM apparatus for performing in situ TEM atomic force microscopy.

Description

MEMS SENSOR FOR IN SITU TEM ATOMIC FORCE MICROSCOPY

Field of the invention

The present invention relates to an atomic force sensor device and in particular a micro electro mechanical system (MEMS) device for AFM studies in situ of a transmission electron microscope (TEM).

Background of the invention

Tremendous efforts are on going within the nanotechnology field of research in order to both develop new products and understand the behavior of materials at the nano scale. This is a truly cross disciplinary field, involving mechanical, electrical, chemical, and biological areas of interest. One of these fields is the material field studying the behavior of materials at the nano scale, developing new materials, and enhancing material characteristics. In order to be able to work within these new fields new instrumentation is currently being developed.

An interesting and growing research field within the nanotechnology field is mechanical indentation and atomic force studies (using an atomic force microscope, AFM) of materials in order to characterize material properties and to understand mechanisms involved in mechanical processes of materials. This is a research field that now is evolving towards the nano area where materials subject to nanoindentation will give answers to many important questions about material properties at the nano scale. Also today many materials or their applications are only available at the nano scale, such as thin films, nanotubes, fullerenes etc. Instrumentation are available that enable such experiments where an object of interest is tested on the nano scale; however, the available instrumentation is quite large in volume and can only perform one type of measurement at a time due to this. For instance, the instrument can perform a nanoindentation on the object and then the object needs to be transferred to another instrument for analysis of the resulting indentation.

Due to this some instruments have been developed that can view the indentation process with for instance an optical microscope during the indentation process or an atomic force microscope (AFM) after the process. It is not an easy task with the current state of the art to do nanoindentation measurements on very small structures such as nanotubes, as these types of objects can not be localized in a normal microscope. Instead an electron microscope is one of the best suited tools for observing these structures and objects. However, it is very difficult to do nanoindentation experiments in situ of an electron microscope.

There is a need for a small footprint AFM device that may be used for these types of combined measurements, especially in combination with a transmission electron microscope (TEM). In this type of combination a powerful tool for the materials researcher is provided, where the instrumentation provides the possibility to indent the object of interest at the nano scale while simultaneously observing the result using the transmission electron microscope. This enables the observation of the dynamic processes involved during the experiment.

MEMS stands for Micro electro mechanical Systems, a manufacturing technology used to produce electromechanical systems using batch fabrication techniques similar to those in IC manufacturing (Integrated Circuits). MEMS integrate mechanical structures, such as sensors and actuators, and electronics on a substrate (e.g. silicon) using micromachining. The idea of using silicon for fabrication of mechanical structures has been done since 1980's due to its outstanding mechanical properties in miniaturized systems. Thanks to the IC industry silicon is produced with very few defects at a low cost. A combination of silicon based microelectronics and micromachining allows the fabrication of devices that can gather and process information all in the same chip. This introduces powerful solutions within for instance automobile production, scientific applications and medical industries.

It is the object of this invention to provide such a nanoindentation or atomic force microscope device that is small and versatile enough to be implemented inside a TEM or any other electron microscope device, e.g. scanning electron microscope (SEM).

Summary of the invention The present invention relates to a MEMS (micro electro mechanical system) or NEMS (nano electro mechanical system) sensor structure used as a force sensing device in a nanoindenter or in an atomic force microscope.

This is provided for in a number of aspect in which a first is a force sensor fabricated in a micro or nano machined process, wherein said force sensor comprise: a holding structure arranged to be held in a sensor holder; contact areas located on the holding structure; a cantilever; a peizoresistive area located on the cantilever; a tip formed on the cantilever at a distal end on the cantilever away from the holding structure and located on a side of the cantilever coinciding with the contact areas;

The force sensor may further comprise an alignment marker located in relation to the tip.

The force sensor may further comprise a dummy cantilever with a piezoresistive area used for temperature compensation.

The piezoresistive area may be coated with a protective coating.

The sensor holder may arranged to be located in a sample holder arrangement for an electron microscope.

The electron microscope may be one of a transmission electron microscope and a scanning electron microscope.

The outer dimensions of the sensor may be less than 2.4 mm x 1.3 mm in one plan, or the outer dimensions of the sensor may be equal to or less than 1.2 mm x 1.3 mm or more preferably equal to or less than 0.9 mm x 1.3 mm in one plane.

The force sensor may further comprise a Wheatstone bridge in connection with the piezoresistive area of the cantilever. The force sensor may further comprise a Wheatstone bridge in connection with the piezoresistive area of the cantilever and the dummy cantilever.

The holding structure may be faceted with an angle of 20 degrees at an end where the cantilever is located.

Another aspect of the present invention is provided, a method for producing a force sensor, comprising the steps of: providing a silicon on insulator wafer with an n-type device layer substrate; fabricating a tip using silicon oxide as mask; shaping the tip; removing the silicon oxide; fabrication of a Wheatstone bridge; forming ohmic contacts with the substrate using diffusion doping of the substrate; forming resistive areas using ion implantation of boron; forming substrate contact areas by doping an n+ area; depositing metal contacts on insulating oxide with via holes to the doped n+ areas; shaping the cantilever using shallow etching with protection on the tip.

The step of fabricating the tip may comprise using an isotropic silicon etch.

The step of shaping the tip may comprise using a thermal oxidation process.

The piezoresistive area may be formed in a U-shape.

The dimensions of the piezoresistive area may be optimized depending on desired resonance frequency of the cantilever.

The step of providing a mask may use plasma enhanced chemical-vapor deposition of silicon oxide.

The step of forming resistive areas may be performed using doped p-types areas.

The metal contacts may be formed using Ti/Au. Yet another aspect of the present invention is provided, a system for measuring atomic force interactions in a TEM, comprising a sensor as described in claims 1 to 12; measurement and control electronics; a sample holder arrangement comprising sample holder, sensor holder and optionally pre conditioning electronics, arranged to hold the sensor, further arranged to fit in situ of a transmission electron microscope; and means for analyzing data obtained from the sensor.

The sensor may be wire bonded to a printed circuit board.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Brief description of the drawings

In the following the invention will be described in a non-limiting way and in more detail with reference to exemplary embodiments illustrated in the enclosed drawings, in which:

Fig. 1 illustrates an experimental setup according to the present invention;

Fig. 2 illustrates a side view of a specimen holder according to the present invention;

Fig. 3 illustrates a sketch of the sensor according to the present invention;

Fig. 4a to 4j illustrates a schematic production process according to the present invention;

Fig. 5 illustrates some results from measurements using the present invention.

Fig. 6 illustrates a schematic block diagram of a close up a sample region in a TEM with a sensor according to the present invention;

Fig. 7 illustrates a schematic block diagram of a processing device according to the present invention; Fig. 8 illustrates in a schematic perspective view part of a sensor according to the present invention;

Detailed description of the invention

Fig. 1 illustrates a schematic view of an experimental setup system according to the present invention. In a preferred embodiment of the present invention a nanoindenter 105 is provided for a transmission electron microscope (TEM) 101. The nanoindenter is mounted on a TEM sample holder 104, and movement and measurement data is acquired using a measurement system comprising control electronics 107 and a computational system 108 comprising e.g. a personal computer, display unit and interface peripherals (such as a keyboard and mouse).

The TEM 101 operates by forming a beam of electrons directed towards a sample and after interaction with the sample, the electron beam is directed towards an image viewing or collecting device 110 using magnetic lenses 102 and 103 respectively. The electron beam is produced using an electron emitting device 109. The TEM 101 is controlled by a TEM control system 106 as understood by the person skilled in the art. However, it is possible to combine the nanoindentation control system 108 with the TEM control system 106. The present invention may be used in any type of standard or non-standard TEM solution, e.g. standard TEM's such as TEM instruments from the FEI Tecnai series or JEOL JEM 2010 series. FEI and JEOL are two of the largest TEM manufacturers in the world.

The present invention presents a MEMS (or NEMS) Atomic Force Microscope (AFM) sensor for use inside a Transmission Electron Microscope (TEM). This enables direct in situ TEM force measurements in the nano N range. The main design challenges of the sensor are high sensitivity and narrow dimensions of the pole gap inside the TEM. Fabrication of the sensor was done using standard micro (or nano) machining techniques, such as ion implantation, oxide growth and deep reactive ion etch. We also present in situ TEM force measurements on nanotubes, which demonstrate the ability to measure spring constants of nanoscale systems.

Design of MEMS Atomic Force Microscope (AFM) sensor There are several considerations when making the force sensor TEM compatible. First of all it must be small enough to fit in the confined space of the TEM pole gap, which is typically around 4 mm. The TEM specimen holder used here is about 2.4 mm thick and the Printed Circuit Board (PCB) onto which the sensor is mounted has the dimensions of 4x2.4 mm². Including margins for wire bonding, this leaves 2.4x1.3 mm² for the base of the sensor. Another requirement to consider is that the tip of the AFM cantilever is preferably centered in respect of the electron beam direction 201. as sketched in Fig. 2, which shows a side view image of the specimen holder and a zoom in sketch showing a top view (i.e. a view in the direction of the e-beam) of the mounting of the sample 204 and sensor_200. This sets the final sensor dimension to 1.2x1.3 mm². To miniaturize the sensing device, an integrated detection with piezo resistive elements arranged in a full Wheatstone bridge was chosen. For additional temperature compensation one of the bridge resistors was placed on a dummy cantilever 301, as seen in the sketch of the sensor in Fig. 3a. The TEM specimen holder 202 can be rotated up to 35° (in the α-direction as shown in Fig. 2 and 3a) and in order to avoid shadowing of the cantilever tip during rotation, the sensor was faceted 20°.

Furthermore, the system with a TEM sample holder comprises a connectivity unit, e.g. a pogo block 205 and a sample positioning device 206. All is arranged in the TEM specimen holder frame 202.

The steps for the fabrication of the MEMS force sensor are schematically drawn in Figs. 4a - 4j and Fig. 8. The starting material is a SOI (Silicon On Insulator) wafer with device layer thickness of 10 μm with a buried oxide layer 2 μm thick, having a resistivity of 1-10 Ω-cm. The device layer is n-type (Fig. 4a).

The tip 800 is fabricated in the first step using isotropic SF₆ (an isotropic silicon etch) plasma etch with silicon oxide (SiO₂) as mask. The tip is shaped by the etching and sharpened using an additional thermal oxidation step (Fig. 4b and 4c). This method is excellent for fabrication of AFM tips with high yield over an entire 6" wafer. The SiO₂ is removed completely after the tip fabrication. Next follows the fabrication of the Wheatstone bridge (Fig. 4d - 4h). To form ohmic contacts to the substrate and resistors, N and P-contacts were made with diffusion doping in the n- type substrate (Fig. 4d). Plasma Enhanced Chemical Vapor Deposition (PECVD) SiO₂ was used as mask material during diffusion. The resistor is constituted by a doped p-type area. The resistors were ion implanted with boron. The energy of the implanted ions was 50 keV and the implanted dose was in the range of 1.5xlO¹⁴ - 1.5xlO¹⁵ cm^"2. The resistor doping is patterned in a U form (see Fig. 4f for a perspective view). This design is optimized for different measurement frequencies (resonant frequencies) and then the ratio between the piezo resistor length and the cantilever length will give different results.

The substrate contact is thereafter formed by doping a n+ area (Fig. 4g).

The metal (Ti/Au) contacts are deposited on insulating oxide with via holes to the highly doped areas (Fig. 4h).

Thereafter the cantilever 300 is shaped using a shallow etch, while protecting the tip with thick photo resist (Fig. 4i). The release is done using DRIE (Deep Reactive Ion Etch). The Bosh process is used to have anisotropic etch (straight walls). This technique is required to miniaturize the device down to 0.9x1.3 mm2. The buried oxide acts as material etch stop and is removed using wet etch (buffered oxide HF acid etch). Fig 4j shows a perspective view of the cantilever with contacts and resistor. Only one resistor is shown in this Fig. 4j but there are four such resistors connected in a Wheatstone bridge on the sensor.

It should be also noted that the tip is placed as far out on the cantilever as possible in order to avoid or limit shadowing effects in the TEM (transmission electron microscope). The angle alpha illustrated in Fig. 2a is close to 90° which will yield a smaller overall structure and therefore the sensor is more easily adapted to TEM applications.

The sensor is glued and wire bonded to a ceramic PCB as shown in Fig. 3 b. The complete chip is then mounted in the TEM specimen holder. The ceramic PCB has via-hole connections to the back side where a pogo-block 205 construction leads the electrical connection to the signal amplifying electronics on the holder shaft. The hole in the PCB 305 is an alignment mark 302 to center the cantilever tip. The TEM specimen holder used here was a modified TEM-STM single tilt holder developed at Nanofactory Instruments. The positioning system utilizes piezoelectric movements and inertial sliding coarse motions in three dimensions. This combines the long range movement of the inertial sliding and the sub-nanometer accuracy of the piezotube. The MEMS force sensor is placed on the non-moving side to simplify electrical connections and to keep the sensor as mechanically stable as possible. The sample was glued onto a wire and placed on the moving part as illustrated in Fig. 2.

Sensor characterization The tip radius of the fabricated sensors was about 100 nm (however, other dimensions may be provided depending on fabrication parameters). The tip radius can be optimized further by better protection during the process. Sensors with cantilever thickness of 2.5-5 μm displayed linear IV-curves and a resistor value of around 10 kΩ for the lower doping doses. The balance of the Wheatstone bridge was within 5%. There were however problems with current leakage and it is suspected that this was caused by uneven boron distribution close to the buried oxide. For even thinner cantilevers the IV-curves were no longer resistive. The noise for a 10 kΩ resistor bridge sensor with a bridge voltage of ±2.5 V was measured to 30 μV peak to peak. The theoretical Johnson noise can be calculated using:

where k_B is Boltzmann's constant, T the temperature (in Kelvin), R the resistor value and Δf the bandwidth of the electronics. The noise at room temperature with a resistance value of 10 kΩ and a bandwidth of 1 kHz was calculated to 0.4 μVrms. The peak to peak noise was calculated to 2.5 μV using information about the electronics components. The calculation gives a minimum noise level. We believe that the higher measured noise value is related to the uneven boron distribution. Other noise components such as 1/f noise also contribute to the total noise figure. The force applied (F) on the sensor can be obtained using Hooke's law:

Where U, Δz , S and k_s are the bridge output, the distance the cantilever is deflected, the sensor electrical sensitivity and the spring constant of the sensor, respectively. S was measured in the TEM by pressing the cantilever against a hard surface while monitoring the displacement Δz. k_s was calculated using measured dimensions and simple beam deflection theory. The cantilever dimensions of the sensor used for the presented measurements were estimated using SEM. The length and width of the cantilever was measured to 300 μm and 30 μm respectively and the thickness to 4 μm, giving a spring constant of 3.4 N/m

Fig. 5a and 5b shows an enlarged view of a TEM sample holder with a MEMS force sensor 506 and sample holder 504. In these figures the force sensing device is mounted on the TEM sample holder and the support structure 509 of the sensor is fixed with respect to the frame 501 of the TEM sample holder 500 and the sample holder 504 is mounted on a piezo 502 driven motor mechanism. The piezo driven mechanism operates with an inertial slider principle, wherein an object 504 is mounted on a ball 503 with a plurality of spring legs 508. The ball 503 is rigidly mounted on a piezoelectric device 502 with one or several possible directions of movement depending on electrodes present on the piezoelectric device 502. When a voltage is applied to an electrode on the piezoelectric device 502 it is made to deflect in a certain direction. The ball 503 may thus be made to extend forward and then quickly made to be retracted by rapidly changing the voltage applied to the electrode on the piezoelectric device 502, by inertial forces the sample holder 504 may thus be made to move relative the ball 503. By repeating this movement it is possible to move the sample holder 504 forward, backwards, or to different directions depending on the applied voltage to the piezoelectric device 502, this inertial slider movement principle induces "large" translations up to several micrometers in range. Smaller movements may be produced only by applying voltages to one or several electrodes on the piezoelectric device 502; this may give movements with an accuracy of the order sub Angstrom. In the case of the present invention the sample under observation is mounted on the piezo driven motor mechanism and the force sensor support structure is fixated rigidly on the frame 501 of the TEM sample holder 500.

The force sensor support structure may be mounted on the TEM sample holder in many suitable ways, for instance glued, mounted on a pin, screwed, or mounted in a clamping mechanism for rapid change of force sensor. The invention is not limited to the above described design; it is also possible to switch places between the sample and the force sensor, i.e. to mount the force sensor on the piezo 502 driven motor mechanism and the sample on the frame 501 of the TEM sample holder 500. It should also be understood by the person skilled in the art that other solutions are possible regarding the ball 503 wherein other geometrical structures may be utilized, for instance if only movement in two directions are needed, a cylinder shaped form may be used. The end part of the TEM sample holder wherein, as exemplified in Fig. 3, the force sensor 506 and probe 505 resides may be electrically shielded using a Faradays cage in order to reduce unwanted electrostatic build up due to the electron beam. Such a shield has an opening through which the probe 505 protrudes.

In situ TEM measurements

The sensor was evaluated using an aluminum sample; Fig. 6a shows a measured force-displacement curve measured on an aluminum surface. During retraction the common hysteresis in the force curve is observed. This is usually due to surface forces but the high magnitude of the force observed here suggests that additional adhesion forces were present, such as welding caused by a high e-beam exposure. The TEM-AFM system versatility was tested using iron filled carbon nanotubes. The nanotubes were pressed into the cantilever tip while imaging and monitoring the force in real time by TEM (Fig. 6b). Fig 6c shows the corresponding force-distance plot. The system noise in the TEM was about 100 nN, which is about the same level as obtained in air. The shielding from 50 Hz noise was however better in the TEM, presumably due to shielding by the TEM column. The offset level could be affected by the TEM illumination, possibly caused by secondary electrons and/or X-ray radiation. From the force plot it is possible to extract the force, displacement and the spring constant of the complete system (k_tot) which are related according to Hooke's law, Δz = F/ k_tot. However the force situation is a bit more complicated. To extract the spring constant of the nanoscale system of interest we have to consider that the cantilever is also flexible. The total spring constant, k_tot, can be expressed in terms of the spring constants of the silicon cantilever and the nanotubes.

* "ttnott — (3) k_s + k_nt

Where k_s and k_nt are the spring constants of the sensor and nanotubes respectively. The total spring constant is estimated from the force-distance plot in Fig. 6c to be 1 N/m, giving a spring constant of the twisted nanotubes of 1.4 N/m. These measurements demonstrate the ability of the system to measure spring constants of nanoscale systems.

Fig. 7 illustrates a measurement device 700 for use in a measurement setup according to the present invention. The measurement device 700 may comprise a processing unit 701, such as a microprocessor, FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), or DSP (Digital Signal Processor), one or several memory units 702 (volatile (e.g. RAM) or non-volatile (e.g. hard drive)), and a data sampling unit 703 obtaining data either directly or indirectly from the experimental setup. Data may be obtained through direct sampling with an A/D converter (analog to digital) or collected from another preprocessing device (not shown) and obtained through a communication link (not shown) such as Ethernet or a serial link. The measurement device 700 may further optionally comprise a communication unit 706 for communicating measurement data sampled, analyzed, and/or processed to another device for display or storage purposes for instance. Also the measurement device 700 may further comprise a pre-processing unit 704 and a measurement control unit 705.

The electronics setup may comprise a pre-amplifier or pre conditioning electronics for enhancing the signal and increasing the stability of the signal, the signal may be converted to a voltage signal and amplified to a suitable level in the pre-amplifier in order to reduce problems with disturbance effects often present when using long electrical wiring. Amplification or pre conditioning may for instance be provided close to the sensor or even on the sensor chip itself in order to reduce noise problems. The signal may then further be connected to a complete control and sampling electronics setup or may be connected independently to a measurement system or a sampling circuitry depending on the experimental setup.

The control and sampling electronics setup may comprise control electronics for controlling the piezo driven motor and applying feedback for different applications. In order to retain a certain force on a sample a feedback system is convenient to use. This is especially important in a system where small distances or forces are in action. For a nanoindentation system already minute vibrations and/or temperature differences may cause the system to change any parameters under control relatively large. This may be counteracted by a feedback system measuring a desired feedback parameter and trying to keep this parameter constant. A nanoindenter system may comprise different measurement setup and experimental setup functions controllable from a control system in software or in hardware. These types of functions may include, but is not limited to, different ways of applying force and making indentations on a sample, ramping of force curves, time limited indentations, repeated indentations, and depth limited indentations.

Due to the geometrical configuration of the TEM and nanoindenter/AFM special requirements are set on a sample or the sensor. The sample need to arranged so as to allow the electron beam to pass through the sample or pass close to the sample in such a way that a shadow is formed and the interaction area can be viewed. The sensor needs to be arranged and/or designed in such a way as to decrease the shadowing effect, for instance with the tip formed close to a distal end of the cantilever.

In another embodiment of the present invention, the AFM (Atomic Force Microscope) behaves in much the same way as the nanoindenter where a force sensor is used for measuring forces between the tip and the surface of interest. However, in the indenter case a force is applied, whereas in an AFM case a force is measured for a certain distance between the probe and the surface. For an AFM in so called contact mode, the AFM is not made to press into the object but rather only scan the surface of the object much as a vinyl record player scans a record and measures the topographic profile on the surface. An AFM may be operated in several different modes:

1. Contact mode, wherein the tip has direct physical contact with the surface;

2. Non-contact mode, wherein the tip is vibrated above the surface and changes in the vibration amplitude and/or vibration frequency is measured and these parameters are dependant on the force between the tip and the surface; and

3. Intermittent mode, wherein the tip is vibrating above the surface and just barely touches the surface (this is sometimes called tapping mode) and changes in the amplitude, frequency, and/or phase is measured.

It is possible with careful design of the force sensor according to the present invention to achieve suitable range of force sensitivity for it to operate in an AFM application. By letting the piezo 502 vibrate with suitable frequency depending on the application it may be used in both non-contact mode and intermittent mode. It is also possible to use in normal contact mode. The piezo motor may provide scanning control of the tip. However, in order to keep a correct distance to the surface or maintaining a certain force setting, a feedback system for controlling the tip location may be provided.

A system for doing nanoindentation and/or AFM measurements may comprise not only a force sensor, but also control electronics and analysis hardware and software. The control electronics is used for controlling the movement of the sample or sensor and the movement may be performed by a piezo driven motor such as an inertial slider solution.

To summarize, an in situ TEM AFM system has been developed and evaluated. The sensing device is a custom designed MEMS force sensor manufactured using micromachining methods. The pk-pk noise (peak to peak) of the signal is estimated to 100 nN in the TEM. The versatility of sensor and system was shown by obtaining the spring constant for a nanoscale system inside a TEM.

The force sensor may be used within other application areas apart from in situ of a TEM, for instance in a standard indentation measurement setup in a so called bench top setup. The present invention may find application in both a standalone nanoindentation measurement device or in a combined nanoindentation device and image obtaining device (e.g. an optical microscope or an AFM) or a stand alone AFM.

The TEM-AFM system has been evaluated by performing in situ force measurements on carbon nanotubes where the spring constant of a nanotube pair was measured. Such data in combination with structural dimensions measured in TEM, can be used for extracting material properties such as Young's modulus.

It should be noted that the word "comprising" does not exclude the presence of other elements or steps than those listed and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, and that several "means" may be represented by the same item of hardware. The above mentioned and described embodiments are only given as examples and should not be limiting to the present invention. Other solutions, uses, objectives, and functions within the scope of the invention as claimed in the below described patent claims should be apparent for the person skilled in the art.

Claims

1. A force sensor fabricated in a micro or nano machined process, wherein said force sensor comprise: - a holding structure (303) arranged to be held in a sensor holder; contact areas (304) located on the holding structure; - a cantilever (300); a peizoresistive area (401) located on the cantilever; a tip (800) formed on the cantilever at a distal end on the cantilever away from the holding structure and located on a side of the cantilever coinciding with the contact areas (304);

2. The force sensor according to claim 1, further comprising an alignment marker located in relation to the tip.

3. The force sensor according to claim 1, further comprising a dummy cantilever with a piezoresistive area used for temperature compensation.

4. The force sensor according to claim 1, wherein the piezoresistive area is coated with a protective coating.

5. The force sensor according to claim 1, wherein the sensor holder is arranged to be located in a sample holder arrangement for an electron microscope.

6. The force sensor according to claim 5, wherein the electron microscope is one of a transmission electron microscope and a scanning electron microscope.

7. The force sensor according to claim 1, wherein the outer dimensions of the sensor is less than 2.4 mm x 1.3 mm in one plane.

8. The force sensor according to claim 1, wherein the outer dimensions of the sensor is equal to or less than 1.2 mm x 1.3 mm or more preferably equal to or less than 0.9 mm x 1.3 mm in one plane.

9. The force sensor according to claim 1, further comprising a Wheatstone bridge in connection with the piezoresistive area of the cantilever.

10. The force sensor according to claim 3, further comprising a Wheatstone bridge in connection with the piezoresistive area of the cantilever and the dummy cantilever.

11. The force sensor according to claim 1, wherein the holding structure (303) is faceted with an angle at an end where the cantilever is located.

12. The force sensor according to claim 11, wherein the angle is 20 degrees.

13. A method for producing a force sensor (200), comprising the steps of: providing a silicon on insulator wafer with an n-type device layer substrate; fabricating a tip using silicon oxide as mask; - shaping the tip; removing the silicon oxide; fabrication of a Wheatstone bridge; forming ohmic contacts with the substrate using diffusion doping of the substrate; - forming resistive areas using ion implantation of boron; forming substrate contact areas by doping an n+ area; depositing metal contacts on insulating oxide with via holes to the doped n+ areas; shaping the cantilever using shallow etching with protection on the tip.

14. The method according to claim 12, wherein the step of fabricating the tip comprise using an isotropic silicon etch.

15. The method according to claim 12, wherein the step of shaping the tip comprise using a thermal oxidation process.

16. The method according to claim 12, wherein the piezoresistive area is formed in a U-shape.

17. The method according to claim 12, wherein the dimensions of the piezoresistive area is optimized depending on desired resonance frequency.

18. The method according to claim 12, wherein the step of providing a mask uses plasma enhanced chemical-vapor deposition of silicon oxide.

19. The method according to claim 12, wherein the step of forming resistive areas is performed using doped p-types areas.

20. The method according to claim 12, wherein the metal contacts are formed using Ti/Au.

21. A system for measuring force interactions in a TEM, comprising a sensor according to any of claims 1 to 12; measurement and control electronics; a sample holder arrangement comprising sample holder, sensor holder and optionally pre conditioning electronics, arranged to hold the sensor, further arranged to fit in situ of a transmission electron microscope; and means for analyzing data obtained from the sensor.

22. The system according to claim 21, wherein the sensor is wire bonded to a printed circuit board (305).