Multiple Heaters in a MEMS Device for Drift-Free HREM with High Temperature Changes

Abstract

The use of MEMS-based micro heaters for heating experiments in electron microscopy is known. Heating of a sample typically relates to a temperature increase or decrease of at least 50 K, and often at least 200 K. The present invention provides an improved heating system for use in an observation tool requiring low drift of <0.2 nm/sec, such as an electron microscope, comprising two cooperating and integrated MEMS-based micro heaters (21,22) spaced apart at a mutual distance of less than 10 mm. A first heater is a master heater (21) and capable of receiving a first amount of power, a second heater is a slave heater (22) and capable of receiving a second amount of power, wherein the first and second amounts of power are in a range from 0 mW to the total amount of power. A thermometer is measuring the temperature of the master heater in use with an accuracy of better than 10 mK, and a power controller prevents variation in the total amount of power received by keeping the total amount of power constant with an accuracy of better than 5 pW and divides the total amount of power over the at least two heaters.

Claims

1-15. (canceled)

16. Heating system for use in an observation tool requiring low drift of <0.2 nm/sec, comprising (1) a MEMS heater chip (100), the MEMS heater chip comprising (1a) at least two cooperating and integrated MEMS-based micro heaters (21,22) for receiving a total amount of power, the MEMS heaters spaced apart at a mutual distance of less than 10 mm, (1b) a supporting structure (81) for supporting the micro heaters, the supporting structure having at least one window (71), (2) a temperature controller, the temperature controller comprising a thermometer, characterized in that a first heater is a master heater (21) and capable of receiving a first amount of power, a second heater is a slave heater (22) and capable of receiving a second amount of power, wherein the first and second amounts of power are in a range from 0 mW to the total amount of power, wherein the thermometer measuring the temperature of the master heater in use with an accuracy of better than 10 mK, and (3) a power controller, wherein the power controller prevents variation in the total amount of power received by keeping the total amount of power constant with an accuracy of better than 5 W and divides the total amount of power over the at least two heaters.

17. Heating system according to claim 16, wherein the master heater and slave heater have at least one characteristics that varies less than 10% relative between first heater and second heater, selected from a maximum power, power control, a size, a material of which the heater is constructed, a supporting structure for the heater, a 2- or 3-dimensional layout of the heater, and an Ohmic resistance.

18. Heating system according to claim 16, wherein the master and slave heater are both embedded in silicon nitride.

19. Heating system according to claim 16, wherein at least one MEMS based heater comprise a membrane (21a,22a), the membrane having a thickness of 100 nm-2 m, a length of 10-2000 m, and a width of 10-2000 m.

20. Heating system according to claim 16, wherein a maximum power provision of each of the master and slave heater is from 1-100 mW.

21. Heating system according to claim 16, wherein the MEMS based heaters are selected from a one or two-dimensional structure, a spiral, an ellipsoid, a grid, a branched structure, and a circle.

22. Heating system according to claim 16, wherein the MEMS based heaters are one of free-standing, or partially or fully supported by a membrane.

23. Heating system according to claim 16, wherein the at least two heaters are made of a similar material, selected from Si, SiC, Pt, W and Mo.

24. Experimental set-up for use in an electron microscope comprising a tip (91), a cup in the tip, a sample device in the cup, and the heating system (100) of claim 16.

25. Method of operating an experimental set-up according to claim 24 in an in-situ electron microscope experiment, comprising the steps of providing power only to the slave heater, thermally stabilizing the experimental set-up, and reducing power provision to the slave heater with a first amount, and at the same time increasing power to the master heater with the first amount, and keeping a total power constant.

26. Method according to claim 25, wherein power provision and power division are controlled within 1000 nW, drift is controlled within 0.2 nm/sec, and wherein temperature is controlled within 10 mK.

27. Method according to claim 25, wherein the power of the slave heater is increased to a predetermined value resulting in a temperature from 283-1800 K, and wherein thereafter the power of the master heater is increased to a predetermined value resulting in a temperature from 283-1800 K, and simultaneously the power to the slave heater is decreased.

28. Method according to claim 25, wherein a sample in the sample device is studied at the predetermined temperature.

29. Method according to claim 25, wherein a sample in the sample device is studied during the increase of temperature.

30. Method according to claim 25, wherein the MEMS heater chip is calibrated, and wherein calibration results are used for fine tuning power provision and power division, in view of heat radiation.

Description

FIGURES

[0057] The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying figures.

[0058] FIG. 1 shows a top view of the present device.

[0059] FIG. 2 shows a side view of the present device.

[0060] FIG. 3 shows a side view of a prior art device.

[0061] FIG. 4a-d show HREM images.

[0062] FIG. 5 shows an illustration of drift behaviour when changing the temperature.

DETAILED DESCRIPTION OF THE FIGURES

[0063] In the figures: [0064] 100 MEMS heater chip [0065] 21 master heater [0066] 21a membrane [0067] 22 slave heater [0068] 22a membrane [0069] 25 prior art MEMS heater [0070] 31 electrical contacts [0071] 33 prior art electrical contacts [0072] 51 fixation means [0073] 52 fixing block [0074] 53 prior art fixing block [0075] 56 clamp plate [0076] 56a screw [0077] 57 prior art clamp [0078] 71 window [0079] 75 cut-out section [0080] 81 support [0081] 91 tip

[0082] FIG. 1 shows a top view of the present device. The MEMS heater chip 100 is typically used in combination with a tip 91. At a right hand side the tip is attached and fixed to a microscope using fixation means 51 typically for fixing in an x-direction. The x-direction is indicated with an arrow in the figure. The present device comprises a master heater 21 and a slave heater 22, being at a mutual distance of 0.2 mm. The heating device is fixed to the tip. For fixing the device to the tip, e.g. a clamp plate 56 is used including a screw 56a. The clamp plate may be a separate entity, may be part of the tip, or may be part of the present heating device.

[0083] FIG. 2 shows a side view of the present device. In addition to the elements identified in FIG. 1 also the following details are indicated. The master heater is located above a window 71, allowing inspection of a sample with an electron microscope. A sample (not shown) is typically placed above the window as well. The slave heater is typically placed on a membrane with a cut-out section 75 in the device; the cut out section 75 and the window 71 have similar dimensions. The cut-out section and window may partially or fully overlap, or may be separate. Typically the master heater is placed on a membrane 21a, and the slave heater is also placed on a membrane 22a. Present in the tip is a block 52 for fixing one or more electrical contacts 31. The block and contacts can in principle also be present in the present heating device.

[0084] FIG. 3 shows a side view of a prior art device. Therein a MEMS heater 25 is provided. Further electrical contacts 33, a block 53 for fixing electrical contacts, and a clamp 57 are provided.

[0085] FIG. 4a shows a HREM (TEM) (300 keV) image of typical test sample comprising small and crystalline Au particles deposited on an amorphous SiN substrate with an exposure time of 0.5 sec and a drift of approximately 0.5 A/sec; such a drift is typically acceptable as the resolution is not hampered by specimen drift. In case of drift lattice planes (planes of Au atoms) being more or less perpendicular to the drift direction will be blurred or even absent on the image. In FIG. 4a the drift is so low that the image is almost clear and lattice planes (as present in the specimen) can be observed in all directions.

[0086] FIG. 4b shows a HREM image of the same area As in FIG. 4a with an exposure time of 0.5 sec and a drift of approximately 5 A/sec; such a drift is typically not acceptable as the resolution is severely hampered by specimen drift. As a result of drift the image is almost not clear and details of the image of the individual particles are lost. The arrow indicates the drift direction.

[0087] FIG. 4c shows a Fourier Transform substantially of the image of FIG. 4a. A Fourier Transform may be used to determine the loss of resolution. The image shows a largely regular pattern, reflecting the underlying regular pattern of the image. As some domains can be observed in the image of FIG. 4a, also domains in this decomposed image reflected as a series of points, are visible. The arrows indicate so-called 1.1 A fringes, indicative for the regular pattern in at least two substantially perpendicular directions.

[0088] Likewise FIG. 4d shows a Fourier Transform substantially of the image of FIG. 4b; especially in the drift direction no clear points are observed any more, hence no crystal-lographic information in that direction is apparently present in the image of FIG. 4b. Perpendicular to the drift direction the resolution of FIG. 4b is comparable to that of FIG. 4a as can be observed.

[0089] FIG. 5 shows an illustration of drift behaviour when changing the temperature. On the y-axis the drift in terms of pixels is given. The size of a pixel is about 1 nm. On the horizontal axis time is given, wherein each point represents 5 seconds.

[0090] The figure represents experiments with two heaters on one chip, one indicated with H2, for TEM imaging, and one, indicated with H1, for keeping a total power into the sample device (or chip) the same. In a first stage the heater for imaging is powered. The result thereof is a drift. Over time the drift levels out. At a certain point in time all power is transferred to the other heater (H1). As a result a sudden jump in position of the sample can be observed in the figure. However, the drift itself, so not taking into account the jump, continues along a same line (similar slope and levelling out). Such is indicated in the figure by a second line, wherein the jump is subtracted from the drift observed.

[0091] The figure shows that by first heating the slave heater until the drift is low enough (substantially horizontal in the figure) it is now possible to start providing power (heating) of the heater that is intended to actually heat the sample, without having a drift. Heating can be done at any speed (temperature increase), as long as the total amount of power as received is kept constant, as is the case with the present device.

[0092] Possibly a slight drift may remain, at an order of magnitude smaller than without the present device. The remaining drift can be compensated for, e.g. by control, by calibrating, or a combination thereof.

[0093] A further advantage with the present device is that a larger heat flux towards the sample is now possible with a further advantage that smaller membranes can be used and less bulging occurs.

[0094] The figures have been detailed throughout the description.