Sensor element

Abstract

A sensor element (1) for measuring a temperature is described comprising - a carrier (2), - at least one functional layer (3) arranged on a top side (2a) of the carrier, the functional layer (3) comprising a material having a temperature dependent electrical resistance, - at least one bottom electrode (4), a contact area (c2) being established between the at least one bottom electrode (4) and the functional layer (3), - at least one top electrode (5), a contact area (c1) being established between the at least one top electrode (5) and the functional layer (3), wherein the functional layer (3) is at least partly sandwiched between the at least one bottom electrode (4) and the at least one top electrode (5) and wherein the functional layer (3), the at least one top electrode (5) and the at least one bottom electrode (4) are designed and arranged to achieve a specific electrical resistance of the sensor element (1). Furthermore a use of the sensor element (1) is described.

Description

[0001] Description

[0002] Sensor element

[0003] The present invention relates to a sensor element, preferably a temperature sensor.

[0004] To integrate passive components, such as sensors, capacitors, heaters, etc., the dimensions for modern packaging solutions must be adapted towards micrometer or even nanometer scale. To achieve such miniaturization thin film technologies must be used. For processing, thin film NTC structures are deposited on a substrate, e.g. Si-wafers and can be used in MEMS (Micro Electro Mechanical System) and SESUB (Semiconductor Embedded in Substrate) structures.

[0005] State of the art temperature monitoring and regulation uses ceramic thermistors (NTC) , Silicon-Temperature sensors (KYT) and Platinum temperature sensors (PRTD) or thermoelements (TC) . NTC-thermistors are widely used due to their cheap manufacturing costs. Additionally, they have an advantage compared to thermoelements and metallic resistors (e.g. Ptelements) due to their strong negative resistance- temperature-characteristic .

[0006] For the application in power modules mainly SMD (Surface Mounted Device) NTC temperature elements area used, which are mounted by soldering. For control modules with low power alternatively NTC Chips are used. They are mounted on the bottom side using Ag-sintering paste, soldering, or gluing and contacted on the top side using wire bonds. Therefore, to allow for electrical contacting, the NTC ceramic need metallic electrodes. Those are usually applied as thick film elec- trodes with screen printing using Ag- or Au-paste and following burn in.

[0007] For integration of electrical components in, for example, MEMS or SESUB structures very small, typically smaller than 1000 pm x 1000 pm x 100 pm, elements are needed. Additionally, a compatible contacting method is needed. Classic mounting technologies for SMD and NTC-chips are not suitable.

[0008] It is an object of the present invention to describe a sensor element with improved properties.

[0009] This object is solved by a sensor element and a use of the sensor element according to the independent claims.

[0010] According to one aspect, a sensor element is described. The sensor element is adapted for measuring a temperature. The sensor element is a temperature sensor element. Preferably, the sensor element is an NTC (Negative Temperature coefficient) thermistor. The sensor element is especially adapted for temperature monitoring and / or controlling in automotive applications .

[0011] The sensor element comprises a carrier. The carrier has a top side and a bottom side. The carrier may comprise silicon, silicon carbide or glass (silicates or borosilicates) . Alternatively, the carrier may comprise AIN or AI2O3, for example.

[0012] The top side of the carrier is electrically insulating. This implies, for example, that a carrier comprising silicon needs an insulating layer comprising e.g. SiCt. The carrier may comprise a rectangle or quadratic shape. The sensor element further comprises at least one functional layer. The functional layer is arranged on the top side of the carrier. The functional layer comprises a material having a temperature dependent electrical resistance. The functional layer may be a thin film with NTC properties.

[0013] A material of the functional layer may comprise: a) Oxides: For example Perowskites (based on mixed crystals of the CaMnOs material system where Ca is fully or partially substituted with either Or, Al or La) or Spinell (based on mixed crystals of the NiMn2O4 material system where Ni and / or Mn are partially substituted with Fe, Co, Al) ; b) Carbides, for example (Si,Ti)C, 2H, 4H or 6H, cubic SiC; c) Nitrides for example (Al,Ti)N, CrN.

[0014] The sensor element further comprises at least one top electrode. Of course, the sensor element can comprise more than one top electrode, e.g. two top electrodes or multiple top electrodes. The at least one top electrode may comprise single or multiple layers of thin film metals, with materials comprising Cu, Au, Ni, Or, Ag, Ti, W, Pd or Pt, for example.

[0015] The at least one top electrode is arranged directly above the functional layer. A contact area (i.e. the first contact area) is established between the at least one top electrode and the functional layer. In other words, there is an area of direct electrical and mechanical contact between the top electrode and the functional layer.

[0016] The sensor element further comprises at least one bottom electrode. Of course, the sensor element can comprise more than one bottom electrode, e.g. two bottom electrodes or multiple bottom electrodes. The at least one bottom electrode may comprise single or multiple layers of thin film metals, with materials comprising Cu, Au, Ni, Cr, Ag, Ti, W, Pd or Pt, for example.

[0017] The bottom electrode may be arranged directly on the top side of the carrier. The bottom electrode is arranged directly below the functional layer. A contact area (i.e. the second contact area) is established between the at least one bottom electrode and the functional layer. In other words, there is an area of direct electrical and mechanical contact between the bottom electrode and the functional layer.

[0018] The functional layer is at least partly sandwiched between the at least one bottom electrode and the at least one top electrode. In other words, as seen in a stacking direction of the sensor element, the functional layer is arranged between the bottom electrode the top electrode.

[0019] The sensor element comprises a specific nominal electrical resistance. The functional layer, the at least one top electrode and the at least one bottom electrode are designed and / or arranged and / or connected such that a specific nominal electrical resistance of the sensor element can be achieved. In other words, the functional layer, the bottom electrode and / or the top electrode comprise a specific material, specific contact area and / or a specific position relative to one another to control the resistance of the sensor element. In this way, a very precise sensor element is provided.

[0020] According to one embodiment, the sensor element comprises at least one insulating layer. The sensor element can comprise one, two or multiple insulating layers. Alternatively, the sensor element may be free of an insulating layer. The at least one insulating layer comprises a thin, nonconducting material, for example oxides, nitrides, ceramics, glasses and polymers. The insulating layer may comprise SiCt, for example.

[0021] There are the following possibilities, where an insulating layer may be deposited:

[0022] 1. Between carrier and bottom electrode and / or

[0023] 2. Between bottom electrode and functional layer and / or

[0024] 3. Between functional layer and top electrode and / or

[0025] 4. Between top electrode and a contact pad connected to the top electrode.

[0026] Accordingly, there can be between zero and four insulating layers .

[0027] In other words, the insulating layer may cover at least partly a top side of the sensor element. Additionally or alternatively, the insulating layer may cover at least partly a top side of the bottom electrode. Additionally or alternatively, the insulating layer may cover at least partly the top side of the carrier. The insulating layer may improve the longterm stability of the sensor element.

[0028] The insulating layer may comprise at least one window. The insulating layer can comprise more than one window, e.g. two or multiple windows. The at least one window constitutes a recess in the insulating layer. The window is adapted and arranged to enable an electrical contact between the top electrode / the bottom electrode and the functional layer.

[0029] According to one embodiment, the sensor element comprises at least two contact pads, i.e. at least one first (top electrode) contact pad and at least one second (bottom electrode) contact pad. The contact pads facilitate the electrical connection of the sensor element to an outside.

[0030] The at least one top electrode may function as a contact pad (i.e. the first contact pad) of the sensor element for electrically contacting the sensor element. In this case, an ad- ditional / separate contact pad connected to the top electrode is redundant. Top electrode and contact pad may constitute one single component of the sensor element.

[0031] Alternatively, the sensor element comprises at least one first contact pad, i.e. a separate contact pad, which is electrically connected to the at least one top electrode. In this case, top electrode and contact pad constitute different material layers of the sensor element.

[0032] Also, the at least one bottom electrode may function as a contact pad (i.e. the second contact pad) of the sensor element. In this case, an additional / separate contact pad connected to the bottom electrode is redundant. Bottom electrode and contact pad may constitute one single component of the sensor element. This case may be especially suitable for wire bonding. If an insulating layer is present on the top side of the bottom electrode, the bottom electrode can be connected to a wire via a window in the insulating layer.

[0033] Alternatively, the sensor element comprises at least one (second) contact pad which is electrically connected with the at least one bottom electrode. Again, if an insulating layer is present on the top side of the bottom electrode, the (second) contact pad is connected to the bottom electrode via a window in the insulating layer. According to one embodiment, a resistance of the sensor element is determined / controlled by a size of the contact area between top electrode and functional layer, i.e. by the size of the first contact area.

[0034] For this purpose, the contact area between the bottom electrode and the functional layer (second contact area) must comprise at least the same size as the contact area between the top electrode and the functional layer (first contact area) . Preferably, the second contact area is larger than the first contact area.

[0035] The larger contact area should be at least as large as the smaller one. Ideally, the larger contact area should have an additional length with >3 times a functional layer thickness. Ideally, the size / width of the second contact area c2 is greater than or equal to the size / width of the first contact area cl plus 3 times a thickness of the functional layer .

[0036] The size of the first contact area may be controlled by a size of a window arranged in the insulating layer on the top side of the sensor element.

[0037] According to one embodiment, the resistance of the sensor element is controlled by an area of the top electrode. This can be done if the window size in the insulating layer is larger than the top electrode area or if no insulating layer between top electrode and functional layer is provided, for example.

[0038] According to one embodiment, a resistance of the sensor element is determined / controlled by a size of the contact area between bottom electrode and the functional layer (i.e. the second contact area ) . For this case , the second contact area is smaller than the first contact area .

[0039] Ideally, the si ze / width of the first contact area cl is greater than or equal to the si ze of the second contact area c2 plus 3 times a thickness of the functional layer . In other words , the width of the first contact area should be larger than the width of the second contact area by 3 times the functional layer thickness .

[0040] The si ze of the second contact area may be controlled by a fabrication process of the bottom electrode , i . e . during manufacturing of the sensor element . Additionally or as an alternative , the si ze of the second contact area can be controlled by a si ze of a window arranged in an insulating layer deposited at least partly between bottom electrode and functional layer .

[0041] According to one embodiment , a resistance of the sensor element is controlled / determined by the top electrode and the bottom electrode together . The resistance may be limited by a si ze of the top electrode and a si ze of the bottom electrode .

[0042] In particular, resistance is controlled by a si ze of the first contact area and, at the same time , by a si ze of the second contact area . Additionally or as an alternative , the resistance of the sensor element can be controlled / determined by a position of top electrode and bottom electrode relative to one another, and, in particular, by an overlap area between top electrode and bottom electrode , more precisely by an overlap area between first contact area and second contact area . According to one embodiment , the sensor element comprises at least one bottom electrode and at least two top electrodes . A resistance of the sensor element may be determined / controlled by a si ze of the first contact areas .

[0043] Alternatively or in addition, the resistance of the sensor element may be determined / controlled by a si ze of the second contact area .

[0044] Alternatively or in addition, the resistance of the sensor element may be determined / controlled by a relative position of the top electrodes and the bottom electrode and, in particular, by a si ze of the overlap areas between the top electrodes and the bottom electrode , more precisely by the si ze of the overlap areas between first contact areas and second contact area .

[0045] According to one embodiment , the sensor element comprises a plurality of top electrodes . Moreover, the sensor element comprises a plurality of bottom electrodes . The top electrode and the bottom electrodes are connected in series . This leads to the current passing through the functional layer multiple times in a way as i f multiple smaller resistances are connected in sequence leading to a larger overall resistance of the sensor element .

[0046] The final resistance of the sensor element (nominal resistance ) may be determined by a si ze of the first contact areas and / or by a si ze of the second contact areas . Additionally or alternatively, the resistance of the sensor element may be determined / controlled by a relative position of the top electrodes and the bottom electrodes and, in particular, by a si ze of overlap areas between the top electrodes and the bottom electrodes , more precisely by a si ze of overlap areas between first contact areas and second contact areas .

[0047] Additionally or alternatively, the resistance of the sensor element may be determined / controlled by a number of resistances connected in series . This means , resistance is controlled by controlling the number of times current passing through the functional layer .

[0048] According to one embodiment , the sensor element comprises a narrow resistance tolerance , i . e . a small deviation range from the nominal resistance . For achieving the narrow resistance tolerance , the sensor element further comprises at least one additional contact pad .

[0049] The additional contact pad is connected to at least one of the top electrodes for further adj usting the final resistance of the sensor element . In particular, the additional contact pad enables an additional / in-between connection of at least one of the top electrodes which are connected in series . Unwanted / too frequent current flow through the functional layer, which would increase the overall resistance of the sensor element , can thus be avoided .

[0050] Preferably, the additional contact pad extends beyond a surface of the functional layer . In particular, the additional contact pad is not arranged directly above the functional layer but may be of fset to the side .

[0051] According to one embodiment , the sensor element comprises a narrow resistance tolerance , i . e . a small deviation range from the nominal resistance . For achieving the narrow resistance tolerance , the sensor element further comprises trimming electrodes . The trimming electrodes constitute additional electrodes for enabling additional electrical connections of the top electrodes .

[0052] The trimming electrodes are connected to top electrodes ( in particular only to certain top electrodes ) . The trimming electrodes connect speci fic top electrodes connected in series while omitting other electrodes . Unwanted / too frequent current flow through the functional layer, which would increase the overall resistance of the sensor element 1 , can thus be avoided .

[0053] Preferably, the trimming electrodes are not arranged directly above the functional layer but are of fset to the side .

[0054] According to one embodiment , at least one of the trimming electrodes is trimmed, i . e . electrode material is at least partially removed by for example laser cutting, sawing or grinding, for fine-tuning the resistance of the final sensor element . Through this geometry change the resistance can be changed to better match the rated resistance .

[0055] According to one embodiment , the sensor element comprises a plurality of top electrodes and at least one bottom electrode . The top electrodes are connected in parallel . Alternatively, the sensor element may comprise at least one top electrode and a plurality of bottom electrodes . The bottom electrodes are connected in parallel . Alternatively, the sensor element may comprise a plurality of top electrodes and a plurality of top electrodes . The top electrodes and the bottom electrodes are connected in parallel . A resistance of the sensor element may be determined / controlled by a si ze of the respective first contact area and / or by a si ze of the respective second contact area . Additionally or alternatively, the resistance of the sensor element may be determined / controlled by a number of top electrodes and bottom electrodes connected in parallel .

[0056] According to one embodiment , the sensor element comprises a narrow resistance tolerance . This means that the sensor element has a very small deviation range from the nominal resistance . For achieving the narrow resistance tolerance , the sensor element further comprises trimming electrodes .

[0057] The trimming electrodes are connected to top electrodes ( in particular to all top electrodes ) in a row or circle or spiral . The trimming electrodes may also be connected to random top electrodes . Preferably, the trimming electrodes are not arranged directly above the functional layer but are of fset to the side . At least one of the trimming electrodes can be further trimmed, e . g . cut by a laser, thus omitting speci fic resistances , for fine-tuning the resistance of the final sensor element .

[0058] According to a further aspect , a use of a sensor element is described . The sensor element may be the sensor element described above . All features described in connection with the sensor element apply for the use of the sensor element , as well . The sensor element is used for temperature monitoring and / or temperature controlling, e . g . in automotive applications . As the sensor element comprises a speci fic nominal electrical resistance and a narrow resistance tolerance , a very precise monitoring and / or controlling is enabled . The drawings described below are not intended to be to scale . Rather, individual dimensions may be enlarged, reduced or even distorted for better representation .

[0059] Elements which are similar or which perform the same function are designated with the same reference signs .

[0060] It show :

[0061] Figure 1 an exploded view of a sensor element according to one embodiment ,

[0062] Figure 2 a sectional view of the sensor element according to Figure 1 ,

[0063] Figure 3 a sectional view of the sensor element of

[0064] Figure 2 according to a further embodiment ,

[0065] Figure 4 a sectional view of a sensor element according to a further embodiment ,

[0066] Figure 5 a sectional view of a sensor element according to a further embodiment ,

[0067] Figure 6 a sectional view of the sensor element of

[0068] Figure 5 according to a further embodiment ,

[0069] Figure 7 a sectional view of a sensor element according to a further embodiment , Figure 8 a sectional view of the sensor element of Figure 7 according to a further embodiment ,

[0070] Figure 9 a sectional view of a sensor element according to a further embodiment ,

[0071] Figure 10 a sectional view of a sensor element according to a further embodiment ,

[0072] Figure 11 a sectional view of a sensor element according to a further embodiment ,

[0073] Figure 12 a sectional view of the sensor element of Figure 11 according to a further embodiment ,

[0074] Figure 13 a sectional view of a sensor element according to a further embodiment ,

[0075] Figure 14 a sectional view of the sensor element of Figure 13 according to a further embodiment ,

[0076] Figure 15 a schematic top-down view of the sensor element according to Figures 13 , 14 ,

[0077] Figure 16 a schematic top-down view of a sensor element according to a further embodiment ,

[0078] Figure 17 a schematic top-down view of a sensor element according to a further embodiment , Figure 18 a sectional view of a sensor element according to a further embodiment ,

[0079] Figure 19 a sectional view of the sensor element of

[0080] Figure 18 according to a further embodiment ,

[0081] Figure 20 a schematic top-down view of a sensor element according to Figures 18 , 19 .

[0082] Figures 1 to 3 show a sensor element 1 according to a first embodiment . The sensor element 1 is a temperature sensor . The sensor element 1 is an NTC thermistor .

[0083] The sensor element 1 has a top side la and a bottom side lb . A thickness T of the sensor element 1 is < 100 pm, preferably < 80 pm and ideally < 50 pm . In this regard, the thickness T denotes an extension of the sensor element 1 in a stacking direction, i . e . the extension perpendicular to a main direction of extension of the sensor element 1 .

[0084] The sensor element 1 comprises a carrier 2 having a top side 2a and a bottom side 2b . The carrier 2 preferably comprises silicon, silicon carbide or glass ( silicates or borosilicates ) . Alternatively, AIN or AI2O3 are also possible materials of the carrier 2 .

[0085] The top side 2a of the carrier 2 is electrically insulating . This implies , for example , that a carrier 2 comprising silicon needs an insulating layer 6 comprising e . g . SiCt ( see , for example , Figure 3 ) . A thickness of the insulating layer 6 arranged on the top side 2a of the carrier 2 may be between 50 nm and 1 pm, preferably between 250 nm and 600 nm . Ideal- ly, the thickness is 500 nm. The carrier 2 is preferably a rectangle and may be quadratic. An edge length of the carrier 2 is < 1000 pm, preferably < 800 pm and ideally < 500 pm.

[0086] The sensor element 1 further comprises a functional layer 3. The functional layer 3 comprises a material with special electrical characteristics (temperature dependent electrical resistance) . The functional layer 3 is a thin film with NTC properties .

[0087] Possible materials for the functional layer 3 are: a) Oxides: For example Perowskites (based on mixed crystals of the CaMnOs material system where Ca is fully or partially substituted with either Or, Alor La) or Spinell (based on mixed crystals of the NiMn2O4 material system where Ni and / or Mn are partially substituted with Fe, Co, Al) ; b) Carbides, for example (Si,Ti)C, 2H, 4H or 6H, cubic SiC; c) Nitrides for example (Al,Ti)N, CrN.

[0088] A layer thickness t of the functional layer 3 is between 1 nm and 1 pm, preferably between 100 nm and 500 nm and ideally between 250 nm and 400 nm.

[0089] Moreover, the sensor element 1 comprises a top electrode 5 and a bottom electrode 4. Of course, the sensor element can comprise more than one top electrode 5 / bottom electrode 4 as described in the embodiments in connection with Figures 9 to 20. The top electrode 5 / the bottom electrode 4 may comprise single or multiple layers of thin film metals, with materials being Cu, Au, Ni, Or, Ag, Ti, W, Pd or Pt.

[0090] The bottom electrode 4 is arranged directly on the top side 2a of the carrier 2 (Figures 1 and 2) or on the insulating layer 6 disposed on the top side 2a of the carrier 2 (see Figure 3 ) . The bottom electrode 4 is arranged between the carrier 2 and the functional layer 3 . The bottom electrode 4 is arranged directly under the functional layer 3 . In other words , the bottom electrode 4 is at least partly in direct electrical and mechanical contact with the functional layer 3 . A contact area c2 ( second contact area c2 ) is established between the bottom electrode 4 and the functional layer 3 . The second contact area c2 is that area in which the functional layer 3 directly rests on the bottom electrode 4 .

[0091] The top electrode 5 is arranged on a top side of the functional layer 3 , i . e . above the functional layer 3 . In other words , the functional layer 3 is sandwiched between top electrode 5 and bottom electrode 4 . The top electrode 5 is at least partly in direct electrical and mechanical contact with the functional layer 3 . A contact area cl ( first contact area cl ) is established between the top electrode 5 and the functional layer 3 . The first contact area cl is the area in which the top electrode 5 directly rests on the functional layer 3 .

[0092] As previously mentioned, there can be multiple insulating layers 6 . In the embodiment according to Figures 1 to 3 , the sensor element 1 further comprises an insulating or protection layer 6 which is arranged on a top side la of the sensor element 1 . This insulating layer 6 covers the top side la at least partly, as can be gathered from Figure 2 , for example . An insulating layer 6 further covers a top side of the bottom electrode 4 except for the contact area c2 between bottom electrode 4 and functional layer 3 . An insulating layer 6 also covers a top side of the functional layer 3 expect for the contact area cl between top electrode 5 and functional layer 3 . The respective insulating layer 6 comprises windows or recesses 7 . As there can be multiple insulating layers 6 , there can also be multiple windows 7 . Between bottom electrode 4 and functional layer 3 , there is a window 7 ( Figure 3 ) . Between bottom electrode 4 and contact pad 4a may be another window ( see Figure 1 ) . Between top electrode 5 and functional layer 3 there can be one more window . Between top electrode 5 and contact pad 5a can be a window, as well ( see Figures 1 and 2 ) . And theoretically they can all be present at the same time . Just because one insulating layer 6 has a window 7 it does not mean another insulating layer 6 cannot have one or more windows 7 anymore .

[0093] These window 7 are adapted and arranged to enable direct contact between the top electrode 5 and the functional layer 3 and / or between the bottom electrode 4 and the functional layer 3 and / or between the bottom electrode 4 and the contact pad 4a, etc . In particular, in Figures 1 to 3 , one window 7 is arranged directly below the top electrode 5 to enable electrical contact between the top electrode 5 and the functional layer 3 in the first contact area cl . A further window 7 is arranged directly above the bottom electrode 4 to enable electrical contact between the bottom electrode 4 and a contact pad 4a, which is described later on in detail .

[0094] The respective insulating layer 6 can improve the long-term stability of the sensor element 1 , especially when the insulating layer 6 is arranged on an outer surface of the sensor element 1 . An insulating layer thickness is between 50 nm to 1 pm, preferably 200 nm to 600 nm and is ideally between 400 nm to 500 nm . The respective insulating layer 6 comprises a thin, nonconducting material , for example oxides , nitrides , ceramics , glasses and polymers .

[0095] As mentioned above , one insulating layer 6 covers the top side la of the sensor element 1 with the exception of contact pads 4a, 5a, i . e . first contact 5a and second contact pad 4a . The contact pads 4a, 5a make it easier to electrically contact the sensor element 1 and have a thickness of > 100 nm, preferably > 1 pm and ideally > 5 pm . The contact pads 4a, 5a comprise single or multiple layers of thin film metals with materials being Cu, Au, Ni , Cr, Ag, Ti , W, Pd or Pt , for examp 1 e .

[0096] For integration in SESUB structures , contact pads 4a, 5a comprising Cu are necessary . The thickness of the Cu pads is designed to be the highest points of the sensor element 1 . They reach at least > 1 pm preferably > 3 pm and ideally > 6 pm over the remaining surface of the sensor element 1 . Those Cu- thicknesses are necessary for the processing and reliable contacting in SESUB structures .

[0097] The contact pads 4a, 5a are directly connected with the electrodes 4 , 5 . In the embodiment according to Figures 1 to 3 , the contact pad 4a is connected directly to the bottom electrode 4 via window / recess 7 . Moreover, in this embodiment , the top electrode 5 directly functions as contact pad 5a . In other words , there is no additional first contact pad 5a connected with the top electrode 5 as can be seen from Figures 1 to 3 .

[0098] In an alternative embodiment (not explicitly shown) also the bottom electrode 4 can directly function as contact pad 4a . In other words, in this case, there is no additional second contact pad 4a connected with the bottom electrode 4.

[0099] In an alternative embodiment (see Figure 4) a specific electrode material can be used to contact to the functional layer 3 and to contact the top electrode 5 to improve adhesion (see Fig. 4) . In other words, in the embodiment according to Figure 4, a separate first contact pad 5a is provided which electrically and mechanically contacts the top electrode 5. The materials of top electrode 5 and first contact pad 5a may be different.

[0100] In each case (Figures 1 to 4) , the top electrode 5 is connected directly via the window 7 in the insulating layer 6 to the top side of the functional layer 3 to establish the contact area cl .

[0101] As can be gathered from Figures 2 to 4, the current flow F is from second contact pad 4a to the bottom electrode 4 further to the functional layer 3 and via the functional layer 3 to the top electrode 5, 5a.

[0102] The sensor element 1 comprises a specific resistance (nominal resistance) . In the embodiment according to Figures 1 to 4, the resistance is determined and, in particular limited, by a size of the first contact area cl, i.e. the contact area between top electrode 5 and functional layer 3.

[0103] For limiting the resistance by means of the first contact area cl, the second contact area c2 must comprise at least the same size as the first contact area cl. Preferably, the second contact area c2 is larger than the first contact area cl, as shown in Figures 1 to 4. In particular, a width of the second contact area c2 ( extension of the second contact area c2 perpendicular to the stacking direction) is equal to or larger than a width of the first contact area cl plus three times the thickness t of the functional layer 3 : c2 > cl + 3t .

[0104] The si ze / width of the first contact area cl is controlled by a si ze of the window 7 arranged in the insulating layer 6 directly beneath the top electrode 5 . The larger the window 7 , the larger the first contact area cl . The larger the first contact area cl , the smaller the resistance of the sensor element 1 .

[0105] I f the window si ze is larger than the si ze of the area of the first contact pad 5a and / or in the absence of an insulating layer 6 (not explicitly shown) , the resistance of the sensor element 1 can also be controlled by the area of the top electrode 5 . , In the embodiment according to Figures 1 to 3 the resistance is also controlled by an area of the top electrode 5 as the top electrode 5 functions as first contact pad 5a .

[0106] Figures 5 and 6 show a sectional view of the sensor element 1 according to a further embodiment . In this embodiment , the electrical resistance is controlled using the bottom electrode 4 . In particular, the resistance is determined by the si ze / the width of the second contact area c2 . The larger the second contact area c2 , the smaller the resistance of the sensor element 1 .

[0107] For determining / controlling the resistance by means of the second contact area c2 , the first contact area cl must comprise at least the same si ze as the second contact area c2 . Preferably, the first contact area cl is larger than the sec- ond contact area c2 ( see Figures 5 and 6 ) . In particular, a width of the first contact area cl ( extension of the first contact area cl perpendicular to the stacking direction) is equal to or larger than a width of the second contact area c2 plus three times the thickness t of the functional layer 3 : cl 1 c2 + 3t .

[0108] In this embodiment , the si ze of the second contact area c2 is controlled during manufacturing the sensor element 1 , in particular in the fabrication process of the bottom electrode 4 .

[0109] As for the embodiment in Figure 6 , starting from the carrier

[0110] 2 the bottom electrode 4 is deposited . The contact area c2 can now be either defined by the structure of the bottom electrode 4 or, as in the Figure using a window 7 in an insulating layer 6 . To create this window 7 , a SiCt layer is deposited and for example a hole is etched into the SiCt . Then, over the hole the functional layer 3 is deposited . Therefore , the bottom electrode 4 is an even layer and the functional layer 3 is filling out the window 7 . Then an additional SiCt layer / insulating layer 6 is deposited and another window 7 is created for the top electrode / contact pad 5a, 5a .

[0111] It should be noted that the Figures shown are a very rough description of the layer structure and in truth the windows will lead to a step in the layers on top as well as the thickness of the layer is the same independent of the position .

[0112] Figures 7 and 8 show a sectional view of the sensor element 1 according to a further embodiment . In this embodiment , the resistance is controlled by both the top electrode 5 and the bottom electrode 4 . More precisely, the resistance is con- trolled by a si ze of the first contact area cl established between top electrode 5 and functional layer 3 and by the si ze of the second contact area c2 established between bottom electrode 4 and functional layer 3 .

[0113] Here , the resistance is controlled analogous to the embodiments according to Figures 1 to 6 , i . e . by the si ze of the contact areas cl , c2 . Moreover, the resistance can be controlled by the position of the first contact area cl and the second contact area c2 relative to each other, in particular, by an overlap area o perpendicular to the stacking direction between first and second contact area cl , c2 as indicated in Figures 7 and 8 . The larger the overlap area o , the smaller the resistance .

[0114] Again, there are multiple insulating layers 6 and windows 7 as already described in connection with Figures 1 to 3 . As already described above , the insulating layer 6 between bottom electrode 4 and functional layer 3 can be present to control the si ze of the second contact area c2 via a window 7 in the insulating layer 6 .

[0115] By means of controlling the si ze of the contact areas cl , c2 and / or the position of the contact areas cl , c2 relative to each other, the nominal resistance of the sensor element 1 can be precisely controlled .

[0116] Also in this embodiment , the top electrode 5 can function as first contact pad 5a as shown in Figures 7 and 8 . Alternatively, top electrode 5 and first contact pad 5a can be separate material layers analogous to Figure 4 . Figures 9 to 12 show a sectional view of the sensor element 1 according to a further embodiment . In this embodiment , the functional layer 3 is sandwiched between two top electrodes 5 and one bottom electrode 4 . This causes the current to pass through the NTC multiple times ( see current Flow F) . The current passes through the first top electrode 5 ( left in Figure 9 ) through the functional layer 3 to the bottom electrode 4 . From the bottom electrode 4 the electrical current passes along the bottom electrode 4 to below the second top electrode 5 ( right in Figure 9 ) . There , the current passes through the functional layer 3 to the top electrode 5 .

[0117] The resistance of the sensor element 1 can be controlled in the same way as in the embodiments described above , either by changing / controlling the first contact area cl , the second contact area c2 or by varying the position and si zes of the contact areas cl , c2 . Again, the top electrode 5 can be an additional layer ( see Figures 11 , 12 ) or can be simultaneously with the first contact pad 5a, i . e . the top electrode 5 functions as first contact pad 5a, as shown in Figures 9 , 10 .

[0118] Figures 13 and 14 show a sectional view of the sensor element 1 according to a further embodiment . In this embodiment , multiple top electrodes 5 and multiple bottom electrodes 4 are used and connected in series . A plurality of top electrodes 5 and bottom electrodes 4 are present and thus , a plurality of first contact areas cl and second contact areas 2 are provided which may also be di f ferent in dimensions .

[0119] The speci fic structure leads to the current passing through the functional layer 3 multiple times in a way as i f multiple smaller resistances are connected in sequence leading to a larger overall resistance ( see current flow F in Figures 13 , 14 ) .

[0120] In this embodiment , two factors influence the final resistance of the sensor element :

[0121] First , the first and second contact areas cl , c2 , like the ones mentioned in the embodiments described above . For example , controlling resistance with the si ze of the first contact areas cl using top electrode design or window si ze in the insulating layer 6 , or by using the second contact areas c2 , or by using the si ze and position of both t first and second contact areas cl , c2 simultaneously, as described above . The top electrodes 5 may again be either an additional layer (not explicitly shown) or function as first contact pads 5a simultaneously .

[0122] The other factor for controlling the resistance is how many resistances are connected in sequence . By limiting the resistances connected in sequence , the overall resistance of the sensor element 1 can be determined .

[0123] This also allows for options to fine tune resistance after finished production . With the fine tuning it can be achieved that the final sensor element 1 has a very small deviation range from the nominal resistance .

[0124] For fine tuning, there are two options :

[0125] One option includes the provision of trimming electrodes 8 as shown in Figure 15 . The trimming electrodes 8 are separate / additional electrodes which are connected to certain top electrodes 5 arranged in a row ( Figure 15 ) . Alternatively, the trimming electrodes 8 can be connected to certain top electrodes arranged in a circle or spiral or to random top electrodes (not explicitly shown) . The trimming electrodes 8 are further connected to a contact pad 5a as can be seen in Figure 15 . The trimming electrodes 8 act like short-circuit electrodes . They connect certain / some top electrodes and omit other top electrodes 5 which are arranged in between the connected top electrodes 5 .

[0126] The more often the current flows through the functional layer 3 ( current flow F, Figure 15 ) , the higher the final resistance of the sensor element 1 . By introducing the trimming electrodes 8 , it is possible to prevent the current from flowing through the functional layer 3 more often than intended . Speci fically for the design shown in Figure 15 , this means that in the upper row of top electrodes 5a it can be j umped further to the right with the help of the trimming electrodes 8 such that current flow F through the functional layer 3 and the top electrodes 5a arranged in-between can be avoided . In this case the overall resistance can be reduced .

[0127] For further fine-tuning and depending on the measured resistance one can additionally cut of f the trimming electrodes 8 connected to the top electrode 5 by means of a laser, for example . This means that electrode material of the trimming electrodes 8 is at least partially removed by e . g . laser cutting, sawing, or grinding, for fine-tuning the resistance of the final sensor element 1 .

[0128] In Figure 15 as one example , cutting the one furthers to the left would increase the resistance the smallest increment and each additional cut connection would further increase re- sistance . This allows for very good fine tuning towards the rated resistance of the sensor element 1 .

[0129] Ideally, the trimming electrodes 8 are not arranged directly over the functional layer 3 but to the side as indicated in Figure 15 . In other words , the trimming electrodes 8 are not arranged directly above the top side of the functional layer 3 .

[0130] The embodiment in Figure 15 further shows all top electrodes 5 contacting the bottom electrode 4 through the functional layer 3 . This , however, is not necessary and only a part of the top electrodes 5 may be arranged on the functional layer 3 and may contact the bottom electrode 4 , as it is shown for example in Figure 16 . This would be especially interesting for trimming electrodes by laser cutting, as that allows for even smaller increments in resistance fine tuning .

[0131] The second option for fine-tuning the resistance of the sensor element 1 is to include additional contact pads 9 connecting to top electrodes 5 at other positions . This is shown in Figure 17 . The additional contact pads 9 are an additional way of directly contacting ( certain) top electrodes 5a without the introduction of trimming electrodes 8 .

[0132] Depending on the additional contact pads 9 used for the second connection the resistance can be fine-tuned to achieve the target / nominal resistances . In the shown embodiment , the first contact pad 5a would be the left electrode and the second contact pad would be either the top left contact pad 9 ( lowest resistance ) , the top right contact pad 9 ( slightly higher resistance ) or the right contact pad 9 (highest resistance ) to fine tune to target resistances . Ideally, the contact pads 5a, 9 intended for the electrical contacting of the sensor element 1 to an outside source are not fully above the functional layer 3 but are extending beyond the functional layer 3 , as indicated in Figure 17 .

[0133] Figures 18 , 19 show a sectional view of the sensor element 1 according to a further embodiment . In this embodiment , multiple top electrodes 5 and one bottom electrode 4 are provided and connected in parallel . This allows the current to pass through the functional layer 3 at multiple positions simultaneously as shown in Figures 18 , 19 ( see current flow F) .

[0134] Here , as well two factors influence the total resistance of the sensor element :

[0135] First , as described in the previous embodiments , the si ze and relative positions of the contact areas cl , c2 .

[0136] The second factor is the number of electrodes 4 , 5 which are connected in parallel . This embodiment also allows for trimming in the electrodes and fine-tuning the resistance after producing the sensor element 1 . One fine-tuning example is shown in Figure 20 .

[0137] The sensor element 1 shown in Figure 20 comprises one bottom electrode 4 with multiple top electrodes 5 . Also in this embodiment , trimming electrodes 8 are introduced which are connected with all top electrodes 5 in a row . The trimming electrodes 8 can be trimmed by laser cutting for adj usting the final resistance of the sensor element 1 and, thus , for providing a sensor element 1 having a small deviation range from the nominal resistance . Individual resistances can be removed by laser-cutting the trimming electrodes 8 , thereby increasing the overall resistance of the sensor element 1 .

[0138] Preferably, the trimming is done in an area not directly above the functional layer 3 . The bottom electrode 4 can also be split into multiple electrodes , while still maintaining the parallel circuit . Alternatively, the structure can also be mirrored with multiple bottom electrodes 4 and one large top electrode 5 (not explicitly shown) . In this case also the top electrode 5 can be split into multiple electrodes while maintaining the parallel circuit .

[0139] The description of the obj ects disclosed herein is not limited to the individual speci fic embodiments . Rather, the fea- tures of the individual embodiments can be combined with each other in any way - as far as this makes technical sense .

[0140] List of reference signs

[0141] 1 Sensor element la Top side of sensor element lb Bottom side of sensor element

[0142] 2 Carrier

[0143] 2a Top side of the carrier

[0144] 2b Bottom side of the carrier

[0145] 3 Functional layer

[0146] 4 Bottom electrode

[0147] 4a Contact pad / Second contact pad

[0148] 5 Top electrode

[0149] 5a Contact pad / First contact pad

[0150] 6 Insulating layer

[0151] 7 Window

[0152] 8 Trimming electrode

[0153] 9 Additional contact pad

[0154] T Thickness of the sensor element t Thickness of the functional layer o Overlap area between top electrode and bottom electrode cl Contact area between top electrode and functional layer / first contact area c2 Contact area between bottom electrode and functional layer / second contact area

[0155] F Current flow

Claims

Claims1. Sensor element (1) for measuring a temperature comprising- a carrier ( 2 ) ,- at least one functional layer (3) arranged on a top side (2a) of the carrier, the functional layer (3) comprising a material having a temperature dependent electrical resistance,- at least one top electrode (5) , a first contact area (cl) being established between the at least one top electrode (5) and the functional layer (3) ,- at least one bottom electrode (4) , a second contact area (c2) being established between the at least one bottom electrode (4) and the functional layer (3) , wherein the functional layer (3) is at least partly sandwiched between the at least one bottom electrode (4) and the at least one top electrode (5) and wherein the functional layer (3) , the at least one top electrode (5) and the at least one bottom electrode (4) are designed and arranged to achieve a specific electrical resistance of the sensor element ( 1 ) .

2. Sensor element (1) according to claim 1, comprising at least one insulating layer (6) , wherein the insulating layer (6) covers at least partly a top side (la) of the sensor element (1) and / or at least partly a top side of the bottom electrode (4) and / or at least partly a top side (2a) of the carrier (2) .

3. Sensor element (1) according to claim 2, comprising at least one window (7) , the at least one window (7) being a recess in the at least one insulating layer (6) , wherein the at least one window (7) is adapted and arrangedto enable an electrical connection between the bottom electrode (4) and the functional layer (3) and / or between the top electrode (5) and the functional layer (3) .

4. Sensor element (1) according to any one of the previous claims , wherein the at least one top electrode (5) functions as a first contact pad (5a) of the sensor element (1) for electrically contacting the sensor element (1) or wherein the sensor element (1) comprises at least one first contact pad (5a) which is electrically connected with the at least one top electrode (5) .

5. Sensor element (1) according to any one of the previous claims , wherein the at least one bottom electrode (4) functions as a second contact pad (4a) of the sensor element (1) or wherein the sensor element (1) comprises at least one second contact pad (4a) which is electrically connected with the at least one bottom electrode (4) .

6. Sensor element (1) according to claim 4, wherein a resistance of the sensor element (1) is determined by an area of the first contact pad (5a) .

7. Sensor element (1) according to any one of the previous claims , wherein a resistance of the sensor element (1) is determined by a size of the first contact area (cl) established between top electrode (5) and functional layer (3) .

8. Sensor element (1) according to claim 7,wherein the second contact area (c2) comprises at least the same size as the first contact area (cl) .

9. Sensor element (1) according to claim 7 or claim 8, wherein a width of the second contact area (c2) is equal to or larger than a width of the first contact area (cl) plus 3 times a functional layer thickness (t) : c2 > cl + 3t.

10. Sensor element (1) according to any one of claims 7 to 9, wherein the size of the first contact area (cl) is controlled by a size of a window (7) arranged in an insulating layer (6) on the top side (la) of the sensor element (1) .

11. Sensor element (1) according to any one of claims 1 to 5, wherein a resistance of the sensor element (1) is determined by a size of the second contact area (c2) and wherein the second contact area (c2) is smaller than the first contact area ( cl ) .

12. Sensor element (1) according to claim 11, wherein a width of the first contact area (cl) is equal to or larger than a width of the second contact area (c2) plus 3 times a functional layer thickness (t) : cl 1 c2 + 3t.

13. Sensor element (1) according to claim 11 or claim 12, wherein the size of the second contact area (c2) is controlled by a fabrication process of the bottom electrode (4) and / or by a size of a window (7) arranged in an insulating layer (6) disposed at least partly on the top side of the bottom electrode (4) .

14. Sensor element (1) according to any one of claims 1 to 5,wherein a resistance of the sensor element (1) is determined by a size of the first contact area (cl) and by a size of the second contact area (c2) and / or by a position of first contact area (cl) and second contact area (c2) relative to one another .

15. Sensor element (1) according to claim 14, wherein the resistance of the sensor element (1) is determined by a size of an overlap area (o) between first contact area (cl) and second contact area (c2) .

16. Sensor element (1) according to any one of claims 1 to 5, comprising at least two top electrodes (5) , wherein a resistance of the sensor element (1) is controlled by a size of the respective first contact area (cl) and / or by a size of the second contact area (c2) and / or by a relative position of first contact area (cl) and second contact area (c2) and / or by a size of overlap areas (o) between first contact area (cl) and second contact area (c2) ) .

17. Sensor element (1) according to any one of claims 1 to 5, comprising a plurality of top electrodes (5) and a plurality of bottom electrodes (4) connected in series, wherein a resistance is determined- by a size of the respective first contact area (cl) and / or- by a size of the respective second contact area (c2) and / or- by a relative position of the first contact areas (cl) and the second contact areas (c2) and / or- by a size of overlap areas (o) between first contact areas (cl) and second contact areas (c2) and / or- by a number of resistances connected in series.

18. Sensor element (1) according to claim 17,comprising a narrow resistance tolerance, wherein the sensor element (1) further comprises at least one additional contact pad (9) connected to at least one of the top electrodes (5) for fine-tuning the resistance of the sensor element (1) , wherein the additional contact pad (9) extends beyond a surface of the functional layer (3) .

19. Sensor element (1) according to claim 17, comprising a narrow resistance tolerance, wherein the sensor element (1) further comprises trimming electrodes (8) connected to certain top electrodes (5) .

20. Sensor element (1) according to claim 19, wherein at least one of the trimming electrodes (8) is cut by a laser for fine-tuning the resistance of the final sensor element ( 1 ) .

21. Sensor element (1) according to any one of claims 1 to 5, comprising a plurality of top electrodes (5) connected in parallel and at least one bottom electrode (4) or comprising at least one top electrode (5) and a plurality of bottom electrodes (4) connected in parallel or comprising a plurality of top electrodes (5) and a plurality of bottom electrodes (4) connected in parallel, wherein a resistance of the sensor element (1) is determined- by a size of the first contact areas (cl) and / or- by a size of the second contact areas (c2) and / or- by a number of top electrodes (5) and bottom electrodes (4) connected in parallel.

22. Sensor element (1) according to claim 21, comprising a narrow resistance tolerance,wherein the sensor element (1) further comprises trimming electrodes (8) connected to the top electrodes (5) in a row and wherein at least one of the trimming electrodes (8) is cut by a laser for fine-tuning the resistance of the final sensor element (1) .

23. Use of a sensor element (1) according to any one of the previous claims for temperature monitoring and / or temperature controlling .

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