Patent Description:
Internal combustion engines such as, but not limited to, diesel and gasoline engines, may include one or more temperature sensors at least partially disposed within the exhaust system. These temperature sensors sense the temperature of the exhaust gas and may be used by an engine control system to adjust one or more properties of the engine such as air/fuel ratio, boost pressure, timing or the like. These temperature sensors typically operate under thermodynamically and chemically aggressive ambient conditions at temperatures above <NUM>° C.

<CIT> discloses a method of making a temperature sensor. A trimming process is employed to obtain a sensing element having a desired resistance value. Following the trimming, the assembly may be refired. After refiring, the assembly may then be subjected to a fine trimming process in order to obtain the desired resistance value to enhance the first trimming. Following the refiring and fine trimming processes, a cover plate is attached over the sensing element.

<CIT> discloses a thin film resistance element temperature sensor. Trimming is performed to adjust a resistance value of the resistance element before or after formation of the barrier layer.

<CIT> discloses a temperature sensor comprising: a substrate having a calibration portion and a cover layer, wherein at least a portion of the calibration structure is free of contact with the cover layer and at least a portion of the calibration structure is in contact with the cover layer, wherein the calibration structure has been modified by adjusting a first calibration portion being in contact with the cover layer before placement of the cover layer in contact with at least a portion of the calibration structure and wherein the calibration structure has been modified to a nominal resistance value by adjusting a second calibration portion subsequent to placement of the cover layer in contact with at least a portion of the calibration structure.

<CIT> discloses a method for manufacturing a planar sensor comprising: disposing a film of a material (platinum, rhodium, palladium and mixtures and alloys comprising at least one of the foregoing materials) on a substrate; annealing the material; measuring a resistance value of the material; laser trimming the annealed material; heat treating the laser trimmed material; and laser trimming the heat treated material to form the sensor.

For the production of high temperature sensors, usually a Platinum resistive layer is applied on a metal oxide ceramic substrate during their production. The calibration of the sensor is realized by adjustment of the Platinum meander resistance and is performed during the production process but before the passivation completion and protective envelope placement. After the completion of the production of the sensor, the Platinum passivation layer(s) and the protective envelopes may include glass and/or ceramic and/or composite layer(s) resulting in a less accurate sensing element.

What is needed is a temperature sensor with improved accuracy.

According to various embodiments, a method of manufacturing a sensor is provided. The method can include depositing a metal layer on a substrate and fabricating a calibration structure having a first calibration portion and a second calibration portion on the metal layer. The method can further include performing a first calibration of the sensor by modifying the first calibration portion. Further, the method can include placing a cover layer on a portion of the first calibration portion and performing a second calibration of the sensor by modifying the second calibration portion after placing the cover on the first calibration portion.

In some embodiments, modifying the first calibration portion can be performed by modifying a meander structure by removing material. In some embodiments, modifying the second calibration portion can be performed by removing material.

In some embodiments, fabricating the second calibration portion can include fabricating, on the metal layer, at least one of: a structure having a rectangular shape, a structure having a ladder shape, or a structure having a spherical shape.

According to various embodiments, a sensor is provided. The sensor can include a substrate having a calibration structure including a first calibration portion and a second calibration portion. The sensor can further comprise a cover layer in contact with the first calibration portion; wherein at least a portion of the second calibration portion is free of contact with the cover layer and wherein the second calibration portion has been modified subsequent to placement of the cover layer in contact with the first calibration portion.

In some embodiments, the first calibration portion can include a meander structure. In some embodiments, the second calibration portion can include a structure having a rectangular shape, a structure having a ladder shape, or a structure having a spherical shape. In some embodiments, at least one of the first and second calibration portions has been modified by the removal of material. In other embodiments, the first calibration portion can be electrically connected in series with the second calibration portion.

According to various embodiments, a sensor is provided. The sensor includes a substrate, a meander structure provided on the substrate, and a calibration portion provided on the substrate and coupled to the meander portion. The sensor can further include a first cover layer in contact with the meander portion and not in contact with the calibration portion, wherein the calibration portion can be modified subsequent to placement of the first cover layer in contact with the meander portion.

In some embodiments, the calibration portion can be modified by removal of material subsequent to the placement of the first cover layer. In some embodiments, the calibration portion can include at least one of: a structure having a rectangular shape, a structure having a ladder shape, or a structure having a spherical shape. In some embodiments, at least one of the meander portion and the calibration portions can be modified by the removal of material. In some embodiments, the sensor can further include first and second contact pads provided adjacent to one another on the substrate and electrically connected in series with the meander portion and the calibration portion. In some embodiments, the calibration portion can be provided on the substrate between the first and second contact pads. In some embodiments, each of the calibration portion and the meander portion can include a respective amount of resistance for selective reduction, wherein the respective amount of resistance is a function of a respective size, shape, width and thickness.

Various aspects of at least one embodiment of the present disclosure are discussed below with reference to the accompanying figures. It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components may be included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. The figures are provided for the purposes of illustration and explanation and are not intended as a definition of the limits of the aspects of the disclosure.

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. It will be understood by those of ordinary skill in the art that these embodiments may be practiced without some of these specific details. In other instances, well-known methods, procedures, components and structures may not have been described in detail so as not to obscure the described embodiments.

The present disclosure describes a sensor having a specific design to improve its sensing accuracy. The design allows for an additional calibration step during the manufacturing process, therefore, achieving more accurate sensing results.

The calibration process with an additional calibration zone described in the present disclosure can improve the sensor accuracy at <NUM> hour (<NUM>), thus making its performance much better than the known commercial sensors being used in the industry. Further, aspects of the present disclosure reduces the sensor production cost.

For sensors, especially high-temperature sensors, it is desirable to perform fine calibration in order to get accurate sensing results. <FIG> illustrates a known temperature sensor <NUM>. During the production of the high temperature sensors, e.g., sensor <NUM>, a substrate <NUM>, e.g., of metal oxide ceramic, is provided with a Platinum meander <NUM> and contact pads <NUM> and <NUM>. A first passivation layer <NUM> is deposited over the Platinum meander <NUM>.

The calibration of the sensor <NUM> is realized by adjustment of the Platinum meander <NUM> resistance per known techniques, e.g., laser trimming, before wires <NUM>, a second passivation layer <NUM>, cover layer <NUM>, and a cover layer <NUM> are positioned on the substrate <NUM>. The cover layer <NUM> can include two covers, a ceramic cover and a glass cover on top of the ceramic cover. The cover layer <NUM> can be a glass cover. The metal passivation layer(s) <NUM>, <NUM>, and the cover layer <NUM> may include glass and/or ceramic and/or composite layer(s).

As is known, the calibration of the sensor is realized by adjusting the resistance of the Platinum meander <NUM> by increasing the conductor length. The resistance of each sensing element can be adjusted to a nominal value to comply with the desired accuracy specification. The resistance adjustment may be done by laser trimming as explained below.

Referring now to <FIG>, the Platinum meander <NUM> contains resistance loops with different resistances. The loops are connected in parallel with circuit bridges <NUM>.

The first adjustment is by digital trimming. In digital trimming, the resistance of each sensing element is adjusted to a value close to the nominal +/- <NUM> Ohms by adding resistance loops which increases the Platinum meander <NUM> length.

<FIG> shows that during trimming the laser trimmer cuts connecting bridges <NUM> and alters a corresponding loop resistance to the total sensing element resistance.

Further, as is also known, analog trimming is a fine calibration process which adjusts the resistance to the nominal value with accuracy around +/-<NUM> Ohm. This step is performed after the digital trim by cutting. The laser cutting is performed while measuring the resistance value until the nominal value is reached.

<FIG> represents a resistance distribution of the known sensor <NUM>, i.e., the Platinum meander <NUM>, before and after calibration. As <FIG> illustrates with line <NUM>, the resistance distribution is not uniform before the calibration process. However, the resistance distribution is uniform, per line <NUM>, after the calibration process.

As stated above, the calibration of the sensor, e.g., by laser trimming, is implemented during the production process. <FIG> illustrates a known method <NUM> of sensor production with calibration. As <FIG> illustrates, for production of a temperature sensor, a Platinum layer is deposited <NUM> on a substrate and sintered. Then, the sensing element structure is fabricated on the Platinum layer <NUM> followed by a passivation layer <NUM> and then sintered. Passivation is a process of depositing a thin film onto the surface of a micro device in order to modify its electrical characteristics.

The next step <NUM> is the calibration process using laser trimming as described above and which is known to those of ordinary skill in the art. After the sensor is calibrated then a second passivation is performed <NUM> followed by sintering. In the following step, a ceramic layer is placed <NUM> on the second passivation layer and then sintered. Subsequently, the resistance of the sensor is measured <NUM> and then the sensor is diced into rows <NUM>. For production of sensors, it is common to produce multiple sensors on a substrate, e.g., silicon wafer, and then dice the substrate to obtain individual sensors. In dicing process, the substrate is diced into rows and then each row will be diced to obtain a single sensor. The next step of the production is wire welding and attaching or fixing glass dispensing <NUM> followed by sintering. In the wire welding process, the wires <NUM> are welded on to the conductive pads <NUM>, <NUM> and connected to the sensing structure, e.g., meander structure <NUM>, providing electrical connection to the sensing structure. The wires can be metal or metal/ceramic. For example, Platinum, Platinum Rhodium (Pt Rh), Copper, Nickel or any other suitable metal or metal alloy. The next process is depositing glass paste on the welded wires <NUM> followed by sintering. The glass provides mechanical strength and electrical isolation of the conductive structures. In step <NUM>, a glass can seal, or fix, any welded wires and the second calibration portion <NUM> to the substrate <NUM> to make a uniform structure, i.e., the sensor <NUM>. Then the rows will be diced individually <NUM> and the resistance will be checked for the second time, R check <NUM>, <NUM>.

<FIG> illustrate the changes to resistance distribution of the sensor at various steps of the known production process. As <FIG> illustrates, the sensor resistance (R0) distribution <NUM> at the end of the trimming process <NUM> is uniform. Subsequently, however, after step <NUM>, the distribution <NUM> has lost uniformity, and after step <NUM>, the distribution <NUM> has changed even more. This is due to the high temperature exposures (sintering steps) and coefficient of thermal expansion (CTE) mismatches. <FIG> illustrates the resistance distributions measured at steps <NUM> and <NUM>.

The existing designs on a meander structures including calibration loops do not offer a possibility for mitigating, i.e., correcting for the influence of the sintering processes. The known R0 distribution <NUM> requires <NUM>% sorting at the chip level in order to meet the customer specification, causing a financial loss.

As explained above, in known sensors, the Platinum meander design allows a calibration only before completion of the passivation layer(s) and placement of the protective or cover layer. Therefore, the negative impact of the sintering processes to resistance distribution is reflected in the sensor accuracy at the end of the manufacturing process.

Advantageously, the present sensor design in accordance with aspects of the present disclosure includes an additional calibration zone in the sensor structure, i.e., an improved meander structure, to achieve this goal.

As shown in <FIG>, a sensor design <NUM> according to aspects of the present disclosure, can include a substrate <NUM> made of any suitable material, e.g., metal oxide ceramic, alumina oxide ceramic, zirconia oxide ceramic, or a mixture of any of these materials. The sensor <NUM> can include a calibration structure <NUM> fabricated on the substrate <NUM>. The calibration structure <NUM> can be made of any suitable metal, e.g., Platinum, Copper, Nickel, Rhodium, Palladium, or Platinum/Rhodium alloy. The suitable metal or metal alloy can depend on the temperature range and the accuracy of the device and its application. For example, Platinum has a very stable resistance-temperature relationship over the largest temperature range. The calibration structure <NUM> include a first calibration portion <NUM> and a second calibration portion <NUM>. As <FIG> illustrate, the first calibration portion <NUM> can be a meander structure made of, e.g., Platinum. Both, the first calibration portion <NUM> and the second calibration portion <NUM> can be the sensing elements of the sensor <NUM>. The sensor <NUM> can further include wires <NUM> in contact with contact pads <NUM>. In some embodiments, the sensor <NUM> can further include contact pads <NUM> in contact with the wires <NUM> and the contact pads <NUM>. The sensor <NUM> can be exposed to the exhaust gas which causes the resistance between the contact pads <NUM> to change accordingly and the change in resistance is proportional to the temperature of the exhaust gas. In some embodiments, the calibration structure <NUM>, contact pads <NUM> and <NUM>, and wires <NUM> are exposed to the exhaust gas.

The sensor <NUM> can include a first passivation layer <NUM>. The first passivation layer <NUM> is in contact with the substrate <NUM> and at least a portion of the calibration structure <NUM>. In some embodiments, the first passivation layer <NUM> is in contact with the substrate <NUM> and the first calibration portion <NUM>. In some embodiments, the first passivation layer <NUM> is in contact with just the first calibration portion <NUM>. In some embodiments, the first passivation layer <NUM> does not contact the second calibration portion <NUM>. In other embodiments, the first passivation layer <NUM> contacts only a portion of the second calibration portion <NUM>.

The sensor <NUM> can further include a second passivation layer <NUM>. In some embodiments the second passivation layer <NUM> is in contact with the first passivation layer <NUM>. The sensor <NUM> can further include cover layers <NUM> and <NUM>'. The cover layers <NUM> and <NUM>' can be made of any suitable material to protect the sensor <NUM>. For example, the cover layers <NUM> and <NUM>' can be made of glass, ceramic, or composite materials.

<FIG> illustrates a close-up view of the calibration structure <NUM> according to aspects of the present disclosure. The second calibration portion <NUM> can be used for a second calibration step in making the sensor. The first calibration portion <NUM> is electrically connected in series with the second calibration portion <NUM>. As stated above, it is known for sensors to be calibrated once during the production process. Advantageously, the second calibration portion <NUM> enables a second calibration step of the sensor <NUM> further down in the production process, as will be described below.

As <FIG> illustrates, the calibration structure <NUM> can be made of the first calibration portion <NUM>, the second calibration portion <NUM>, and contact pads <NUM>. In some embodiments, the calibration structure <NUM> includes two contact pads <NUM>. In some embodiments, the calibration structure <NUM> includes at least one contact pad <NUM>. In some embodiments, the first calibration portion <NUM> the second calibration portion <NUM>, and the contact pads <NUM> are connected in series. As stated above, the calibration structure <NUM> can be fabricated on a substrate <NUM> by depositing a layer of a metal, e.g., Platinum, followed by a fabrication process. In some embodiments, the contact pads <NUM> are made of a same material as the first calibration portion <NUM> and the second calibration portion <NUM>. In some embodiments, the contact pad <NUM> can be a metal, e.g., Platinum.

The second calibration portion <NUM> can be fabricated and located on any location on the substrate <NUM> as long as it has electrical contact with the first calibration portion <NUM>. In some embodiments, second calibration portion <NUM> is located between the contact pads <NUM>. In some embodiments, the second calibration portion <NUM> is not in contact with the passivation layers <NUM>, <NUM>. In some embodiments, the second calibration portion <NUM> does not contact the passivation layers <NUM>, <NUM> and the cover layer <NUM>. According to the invention, at least a portion of the second calibration portion <NUM> is not in contact with the passivation layers <NUM>, <NUM> and/or the cover layer <NUM>. Having at least a portion of the second calibration portion <NUM> contact free from the passivation layers <NUM>, <NUM> and/or the cover layer <NUM>, enables the second calibration step further down along in the manufacturing process.

The second calibration portion <NUM> can be made in any shape. In some embodiments, the second calibration portion <NUM> has a rectangular shape. <FIG> illustrates some embodiments of the second calibration portion <NUM>. For example, the second calibration portion <NUM> can be made in a rectangle A, round loop B, or ladder design C. Having the second calibration portion <NUM> in the designs as shown in <FIG>, allows the trimmer to cut sections of the second calibration portion <NUM> to modify the resistance of the sensor <NUM> into the desired range.

<FIG> illustrates the sensor <NUM> in an assembled arrangement.

A process (method) <NUM> of manufacturing a sensor according to aspects of the present disclosure is presented in <FIG>. The method <NUM> can include depositing <NUM> a metal layer on a substrate and then sintering. The metal can be any suitable metal, e.g., Platinum. Then, the structure, e.g., sensing element, can be fabricated <NUM> on the metal layer followed by applying <NUM> a passivation layer <NUM>. The next step can be a sintering step.

The following step can be a first calibrating step <NUM> of the sensor <NUM>. The calibration can be digital and/or analog calibration as described above. After the sensor <NUM> is calibrated then the second passivation <NUM> can be performed and the passivation layer <NUM> can be sintered. In the following step <NUM>, a cover layer <NUM> can be placed on the second passivation layer <NUM> and then sintered. The cover layer <NUM> can be made of any suitable material, e.g., glass or ceramic. In some embodiments, the method <NUM> can include placing the cover layer <NUM> on portions of the substrate <NUM> and the second passivation layer <NUM>. In some embodiments, the method <NUM> can include placing the cover layer <NUM> on portions of the substrate <NUM>, the second passivation layer <NUM> and at least a portion of the calibration structure <NUM>. At this step <NUM>, the resistance of the sensor <NUM> (R Check <NUM>) can be measured and the second calibration step can be performed.

The second calibration step can be performed on the second calibration portion <NUM> of the calibration structure <NUM> that is not covered by the first passivation layer <NUM> and/or second passivation layer <NUM>, and/or the cover layer <NUM>. The next step <NUM> can be dicing the sensor <NUM> in rows. The next step <NUM> of the production can be wire welding and attaching or fixing glass followed by sintering. Then the device can be diced individually and the resistance can be checked for the second time <NUM>, R check <NUM>.

As stated above, the second calibration step <NUM> can be performed as part of the first resistance check, e.g., R check <NUM>. According to the invention, 2Ω-6Ω of resistance (depends on contour design) is added to the main structure to compensate the resistance distribution slope. As described above, the method of manufacturing can include two calibration steps in order to reach the nominal value. The nominal value by itself can be chosen depending on the application of the sensor and the desired resistance. In the first calibration step, digital and analog trimming, the resistance value is adjusted to a low value close to the nominal value but not lower than a maximum resistance of the additional contour. For example, adjusting to a nominal value between <NUM>. 00Ω - <NUM>. The second calibration step then can be adjusting all elements to the nominal resistance by modifying the second calibration portion <NUM>, e.g., adjusting to the nominal value of, for example, <NUM>Ω. The amount of resistance to be added can depend on the design of the second calibration portion <NUM>, the width of the first calibration portion <NUM>, a meander width, a thickness of the calibration structure <NUM>, etc. The second calibration portion <NUM> can be protected by the glass or glass ceramic cover together with the wires fixation step of the production process of <FIG>.

<FIG> illustrate the resistance distribution of the resulting sensors, per the method <NUM>, at various steps of the production process according to aspects of the present disclosure. As <FIG> illustrates, the sensor <NUM> resistance <NUM> is relatively constant after the first calibration step <NUM>. The resistance distribution <NUM> of the sensor <NUM> changes after the two passivation processes <NUM>, <NUM> and placement <NUM> of the cover layer. At the first resistance check <NUM>, R check <NUM>, the sensor <NUM> is calibrated again, i.e., the second calibration step as shown in <NUM>. As <FIG> illustrates, the resistance distribution <NUM> measured at the end of the process (R check <NUM>) <NUM> is similar to the resistance <NUM> measured at the second calibration step <NUM>. <FIG> represents a resistance distribution of the sensor <NUM> after the two step calibrations steps <NUM>, <NUM>.

Claim 1:
A method of manufacturing a temperature sensor (<NUM>), comprising:
depositing a metal layer on a substrate (<NUM>, <NUM>);
fabricating a calibration structure (<NUM>) having a first calibration portion (<NUM>) and a second calibration portion (<NUM>) on the metal layer;
performing a first calibration of the temperature sensor (<NUM>) by modifying the first calibration portion, wherein the first calibration includes additional resistance within the range of 2Ω-6Ω;
placing a cover layer (<NUM>, <NUM>) on a portion of the first calibration portion (<NUM>);
placing at least one passivation layer (<NUM>) between the cover layer (<NUM>, <NUM>) and the first calibration portion (<NUM>); and
performing a second calibration of the temperature sensor (<NUM>) by modifying the second calibration portion (<NUM>) to a nominal resistance value after placing the cover layer (<NUM>, <NUM>) on the portion of the first calibration portion (<NUM>).