Abstract:
Microsensors that include an integrated thermal energy source and an integrated temperature sensor are capable of providing localized heating and temperature control of individual sensing regions within the microsensor. Localized temperature control allows analyte detection to be carried out at the same temperatures or substantially the same temperatures at which the sensor is calibrated. By carrying out the sensing near the calibration temperature, more accurate results can be obtained. In addition, the temperature of the sensing region can be controlled so that chemical reactions involving the analyte in the sensing region occur near their peak reaction rate. Carrying out the sensing near the peak reaction rate improves the sensitivity of the sensor which is important as sensor dimensions decrease and the magnitude of the generated signals decreases.

Description:
BACKGROUND 
     1. Technical Field 
     The present application relates to an integrated semiconductor device including a sensor or sensors for sensing and identifying analytes in a sample under investigation. 
     2. Description of the Related Art 
     The demand for microsensors of small dimensions has led to the study of integrated solutions that use techniques and knowledge acquired in the manufacture of semiconductors. In particular, detection and diagnostic devices of a disposable type, which may be connected to external apparatuses for chemical and biochemical analyses, have been studied. 
     Detection and diagnostic devices, utilizing microsensors, comprise a solid substrate, generally of a flat type, bearing a chip, to which particular sensors are connected. These sensors may be sensitive to various analytes, including, for example biomolecules (DNA, RNA, proteins, antigens, antibodies, hormones, etc.), micro-organisms or parts thereof (bacteria, viruses, spores, cells, etc.), and chemicals (oxygen, carbon monoxide, carbon dioxide, glucose, etc.). These microsensors are generally of a type that have limited use, either in the number of times a particular microsensor is used, or in what the microsensor is designed to detect. 
     For example, a common limited use microsensor is used in a handheld blood glucose meter for diabetics. Checking a person&#39;s blood glucose level usually involves a painful prick of a finger to draw out a droplet of blood. The drawn blood is placed in contact with a testing strip, which has a transducer in the form of various electrodes that are sensitive to a chemical reaction between the glucose in the blood and glucose oxidase on one of the electrodes. Signals from the electrodes are detected and processed to determine a blood glucose number that is displayed on a screen to the user. 
     Miniaturization of microsensors translates into smaller sample volumes and requires smaller device dimensions. With the smaller sample volumes and smaller device dimensions, the electric signal produced by an electrochemical sensor can decrease to the order of nano- or pico amperes. With such small electric signals and the need for accurate and reproducible results, controlling the conditions at which the measurements are taken becomes increasingly important. 
     Conditions such as temperature are known to directly affect the rate of chemical reactions. For example, there is an optimum temperature above which the reaction rate between glucose and glucose oxidase does not increase. This temperature sensitivity results in an increasing current output from the transducer as the temperature approaches the optimum reaction temperature and a decreasing current response as the temperature increases beyond the optimum reaction temperature. By controlling the temperature of the microsensor in the local region where the chemical reaction occurs, the current output from the transducer can be maximized which will result in increased sensitivity and a reduction in the effect of interfering signals. 
     The temperature at which a microsensor is used can affect the accuracy of the sensor in other ways. For example, if the sensor is calibrated at a specific temperature and the testing is carried out at a different temperature, the accuracy of the measurement can be adversely affected. 
     In addition, in some bio- or chemical microsensors, the analyte is required to diffuse through a membrane to reach the transducer. The permeability of the membrane can depend on the identity of the diffusing species and the temperature. When the permeability of the membrane is affected by temperature, the accuracy of the measurement will decrease when the measurement is carried out at a temperature different from the calibration temperature. 
     BRIEF SUMMARY 
     Solutions to controlling the temperature at which analytes of interest are detected by a microsensor are described in the present disclosure. In certain embodiments, a semiconductor device including a microsensor capable of detecting a small amount of analyte in a sample is described. In such embodiments, the microsensor produces a signal, e.g., an electric or optical signal, in response to the concentration of analyte present in the sample. The disclosed microsensors include a sensing region formed over a semiconductor substrate. The sensing region includes a transducer that produces a signal in response to an interaction between the analyte and the sensing region. The microsensors include an integrated thermal energy source that produces thermal energy and an integrated temperature sensor that detects the temperature of the sensing region. The thermal energy source and temperature sensor are adjacent to the sensing region and cooperate to provide localized heating and temperature control of the sensing region. 
     By controlling the temperature of the sensing region to be at or near the temperature at which the sensor was calibrated, the accuracy of the measurements can be improved. In addition, the sensitivity of the microsensor can be increased by controlling the temperature of the sensing region to approach the temperature at which an interaction between the analyte and the sensing region is near its peak. For example, in embodiments where the transducer is an electrochemical transducer and the interaction is a chemical reaction, the temperature of the sensing region is controlled to a temperature where the chemical reaction rate is at its maximum. 
     In some embodiments, the thermal energy source is provided below the transducer. In some embodiments, the thermal energy source is also provided below the temperature sensor. In yet other embodiments, both the thermal energy source and the temperature sensor are provided below the transducer. In yet other embodiments, the thermal energy source and temperature sensor do not underlie the transducer. In certain embodiments, the transducer and temperature sensor are formed from the same material. In other embodiments, the transducer and the temperature sensor are formed from different materials. 
     The present disclosure describes that the thermal energy source generates thermal energy that provides localized heating of the sensing region. The integrated temperature sensor detects the temperature of the sensing region and produces a signal indicative of that temperature. That signal can be used by a control unit to control the thermal energy produced by the thermal energy source. Through this feedback loop, localized heating of the sensing region can be adjusted and controlled to achieve the desired temperature. 
     The microsensors described by the present disclosure can be formed as a semiconductor device through a sequence of growing, deposition, patterning, and etching steps. In one embodiment, such a method involves providing a silicon substrate that includes a thermal insulation layer. A thermal energy source layer of a refractory material is formed over the thermal insulation layer. The resulting thermal energy source layer is patterned to form a thermal energy source. A thermal conducting layer is formed over the thermal energy source. After the thermal conducting layer is formed, a working electrode, a counter electrode, and a temperature sensor are formed over the thermal conducting layer. A passivation layer is then formed over the temperature sensor. The passivation layer is patterned to define a sensing region and expose at least a portion of the working electrode and counter electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic view of a cross-section for a microsensor according to one embodiment of the present disclosure; 
         FIG. 2  shows a top plan view of a layout for a microsensor according to one embodiment; 
         FIG. 3  shows a cross-section view taken along line  3 - 3  in  FIG. 2 ; 
         FIGS. 4A-4G  show a cross-section view of different steps in the process flow for making a microsensor in accordance with one embodiment of  FIG. 2 ; 
         FIG. 5  shows a schematic of an alternative embodiment of a microsensor according to the present disclosure; 
         FIG. 6  shows a schematic view of another alternative embodiment of a microsensor of the present disclosure; 
         FIG. 7  shows a schematic view of another alternative embodiment of a microsensor of the present disclosure; and 
         FIG. 8  shows a temperature profile model for a portion of a semiconductor die including a sensing region and thermal energy source in accordance with the embodiment of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the disclosed subject matter. However, the disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and methods of forming the structures associated with semiconductor devices have not been described in detail to avoid obscuring the descriptions of other aspects of the present disclosure. 
     Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising,” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more aspects of the present disclosure. 
     Reference throughout the specification to “chemical or biological element” or “chemical” includes all chemical atoms, parts of atoms, molecules, particulates, biological material, etc. that are sensed and interact with the sensors described herein. The term “chemical” should not be construed narrowly to limit a chemical element solely to an atom or a molecule, but rather, the term “chemical” is broadly construed to cover chemical and biological elements or components thereof. 
     Throughout the following description a transducer is described in terms of an electrochemical transducer that includes a working electrode, a counter electrode and an optional reference electrode. It is noted that the reference to an electrochemical transducer and its electrodes is for illustrative purposes only and is not to be construed as limiting the scope of the described embodiments and appended claims. For example, the transducer may be an electrical transducer that measures surface or electrolyte conductivity. Other examples of transducers include optical (measures fluorescence, reflection, or adsorption) transducers, mass sensitive or heat sensitive transducers. 
     In the drawings, identical reference numbers identify similar features or elements. The sizes and relative positions of the features in the drawings are not necessarily drawn to scale. 
       FIG. 1  shows a microsensor  100  formed as part of a semiconductor device in accordance with the present disclosure.  FIG. 1  is a schematic view that does not show elements such as metal interconnect lines, vias, contact pads, and other conventional features. These features can be provided using known structures and processing techniques. As an overview, in  FIG. 1  sensor  100  includes a sensing region  102  into which a sample (not shown) containing an analyte of interest is received. Sensing region  102  includes a transducer  104  that produces a signal in response to an interaction between the analyte and the sensing region. The sensor also includes a temperature sensor  108 , a thermal energy source  106 , and an underlying thermal insulating layer  202  (e.g., silicon dioxide). Thermal insulating layer  202  is formed on an underlying semiconductor substrate  200 , e.g., silicon substrate. 
     This underlying semiconductor substrate  200  may include various conductive and non-conductive features needed to operate the sensor. For example, semiconductor substrate  200  may include metal interconnect features, vias, contact pads and the like to provide electric power to thermal energy source  106  and process signals from transducer  104  and temperature sensor  108 . These components can be provided using known structures and processing techniques and are not described in detail. 
     Thermal insulating layer  202  thermally insulates underlying semiconductor substrate  200  from thermal energy source  106 . Layer  202  can be formed from silicon dioxide using conventional thermal growth or deposition processes. Other dielectric materials with a similar or lower coefficient of thermal conductivity can be used in place of silicon dioxide. 
     As shown in  FIG. 1 , a thermal energy source  106  is formed on thermal insulating layer  202  adjacent sensing region  102 . The thermal energy source  106  is formed from a refractory material, such as co-sputtered tantalum aluminum, and generates thermal energy in response to the flow of electric current. Materials for forming thermal energy source  106  are not limited to tantalum aluminum. Other refractory materials such tantalum nitride can be used. A layer  204  that preferably has high thermal conductivity is between the thermal energy source  106  and the transducer  104 . 
     Positioned above thermal energy source  106  and forming a part of sensing region  102  is a transducer  104 . Though not shown in  FIG. 1 , transducer  104  includes a plurality of electrodes, for example, a working electrode, counter electrode, and an optional reference electrode formed from inert polarizable metals that are suitable for electrochemistry, including gold, platinum, palladium, and silver. While working electrode, counter electrode, and optional reference electrode are illustrated schematically as a single structure  104  in  FIG. 1 ; it should be understood that transducer  104  comprises multiple electrodes. These electrodes cooperate to detect a change in electrical properties resulting from an interaction between an analyte of interest and the sensing region  102 . For example, when microsensor  100  functions as an electrochemical sensor, the working electrode of transducer  104  may have a chemical receptor (not shown) formed on its surface. For example, the receptors may be biologic cells, antibodies, enzymes, DNA/RNA sequences or customized molecules that chemically react with the analyte of interest in a manner that can be detected by the electrodes. While the present disclosure describes embodiments that employ an electrochemical sensor, other responses to the interaction of the analyte with the sensing region, such as optical, capacitive, frequency, gravimetric and the like can also be used to detect the analyte of interest. 
     In the embodiment illustrated in  FIG. 1 , temperature sensor  108  is adjacent heater  106  and transducer  104 . More specifically, in  FIG. 1 , sensor  108  is above heater  106 . Like transducer  104 , temperature sensor  108  is located within sensing region  102  where it can readily detect a temperature of sensing region  102 . Like transducer  104 , a portion of temperature sensor  108  is exposed and not covered by passivation layer  212 . Temperature sensor  108  can be a thermistor made from a material that exhibits an electrical resistance that changes with temperature, such as platinum or chromium silicide. Temperature sensor  108  can be formed from suitable metals other than platinum or chromium silicide. 
     As shown in  FIG. 1 , portions of transducer  104  and temperature sensor  108  are covered by a passivation layer  212 , formed from a material such as polyimide. Other portions of the transducer  104  and temperature sensor  108  are exposed and not covered by passivation layer  212 . These uncovered portions of transducer  104  and temperature sensor  108  define a sensing region  102  where a sample containing the analyte of interest is received. Once received in the sensing region  102 , the analyte interacts with the sensing region  102 , for example, by undergoing a chemical reaction at the working electrode this chemical reaction is detected as an electric signal by the electrodes of the transducer. 
     While reference is made to a sensing region that relies upon electrochemical principles to detect an analyte, the present invention is not limited to sensing regions that rely on electrochemical principles. For example, the sensing region can rely on other types of interactions between the analyte and the sensing region such as those that produce other types of measurable signals such as optical signals, changes in mass, changes in acoustic properties, changes in thermal conductivity properties or changes in thermal diffusivity properties. 
     Referring to  FIGS. 2 and 3 ,  FIG. 2  shows a top plan view of a microsensor including sensing region  102 , metal features forming thermal energy source  106 , electrodes  206 ,  208  and  210 , and temperature sensor  108  according to a specific embodiment. In this embodiment, the transducer  104  is composed of electrodes  206 ,  208  and  210 .  FIG. 3  shows a cross-sectional view taken along line  3 - 3  in  FIG. 2 . 
     Sensing region  102  includes a counter electrode  206 , a working electrode  208 , and a reference electrode  210 . Counter electrode  206 , working electrode  208 , and reference electrode  210  are electrically connected to contact pads  214  by conventional metal interconnect lines  216  formed as interlayer metallization components. Counter electrode  206 , working electrode  208 , and reference electrode  210  can be connected via contact pads  214  and lines  216  to other devices which might be part of the transducer  104  such as a potentiostat (not shown), and also to an analog-to-digital (ND) converter (not shown), and a microprocessor (not shown) for operating the electrodes, collecting signals, and processing the signals. 
     Temperature sensor  108  extends around three sides of the sensing region  102 . Each end of temperature sensor  108  is connected to a contact pad  218  through a combination of an interlayer via  220  and interlayer metallization lines  222 . Temperature sensor  108  may be connected to additional devices such as an analog/digital converter and a microprocessor to collect electric signals that are related to the temperature of sensing region  102 . The microprocessor is preferably capable of receiving signals from the temperature sensor  108  and controlling the thermal output by thermal energy source  106  based on the signals received from temperature sensor  108 . In this manner, controlled localized heating is provided to the sensing region  102 . 
     As best illustrated in  FIG. 3 , temperature sensor  108  is covered by a passivation layer  212 . In this embodiment, the temperature sensor  108  is covered by layer  212  at all locations and not exposed to the open environment as shown in  FIG. 1 . Portions of counter electrode  206 , working electrode  208 , and reference electrode  210  remain exposed through an opening in passivation layer  212 . This opening defines a well for receiving a sample. When the temperature of sensing region  102  changes, the temperature as sensed by temperature sensor  108  will change, resulting in a change in the resistance of temperature sensor  108 . This change in resistance can be detected and converted into a temperature reading using known components and techniques. Accordingly, temperature sensor  108  is able to sense the temperature of the sensing region  102 . As described above, the temperature sensed by temperature sensor  108  can be utilized by a microprocessor to control the thermal output of thermal energy source  106 . 
     In the embodiment of  FIGS. 2 and 3 , located below counter electrode  206 , working electrode  208 , reference electrode  210 , and temperature sensor  108  is a thermal energy source  106 . Thermal energy source  106  is separated from temperature sensor  108  and electrodes  206 ,  208 ,  210  by a thermal conducting layer  204 . Thermal energy source  106  is a serpentine element with each end electrically connected to separate contact pads  224  by interconnect metallization lines  226 . Thermal energy source  106  is separated from underlying silicon substrate  200  by thermal insulating layer  202  formed from a material having a thermal conductivity similar to silicon dioxide. 
     By providing the thermal energy source  106  directly adjacent to, e.g., below, the sensing region  102 , localized heating can be provided to the sensing region. Localized heating has the advantage of not affecting the temperature of adjacent sensing regions where different interactions would be sensed. In addition, localized heating heats the regions of interest, i.e., sensing region, while minimizing heating of regions outside the sensing region that may contain components adversely affected if they were heated to the same temperatures as the sensing region. 
     In addition to the arrangement of thermal energy source  106  and temperature sensor  108  shown in  FIGS. 1-3 , other arrangements can provide localized heating as described below with reference to  FIGS. 5-7 . 
       FIGS. 4A-4G  show one method for forming a semiconductor device that includes a microsensor in accordance with the present disclosure. As shown in  FIG. 4A , the microsensor is formed on a silicon substrate  200  on which a thermal insulating layer  202  of silicon dioxide has been formed using known techniques such as thermal oxidation. 
     As shown in  FIG. 4B , a layer  402  of a refractory material such as tantalum aluminum is deposited over thermal insulating layer  202 . Tantalum aluminum can be deposited using known metal deposition techniques such as a sputtering or chemical vapor deposition. After the tantalum aluminum is deposited, a layer  404  of aluminum is deposited thereover. Aluminum layer  404  can be deposited using known metal deposition techniques, such as physical vapor deposition. Following the formation of tantalum aluminum layer  402  and aluminum layer  404 , the aluminum layer  404  is patterned to form contacts and interconnect lines not shown in  FIG. 4C  but shown in  FIG. 2  to form interconnect lines such as  216 ,  222 ,  226 , etc. Tantalum aluminum layer  402  is then patterned to form thermal energy source  106 . The formed thermal energy source  106  is then covered with a thermal conducting layer  204  as shown in  FIG. 4D . Thermal conducting layer  204  is formed from materials that have thermal conductivity properties that promote the conduction of thermal energy from thermal energy source  106  to sensing region  102 . Thermal conducting layer  204  can be formed from materials such as silicon nitride or silicon carbide. Deposition of silicon nitride or silicon carbide can be carried out using known techniques, such as chemical vapor deposition. The deposited thermal conducting layer  204  is patterned to form vias (not shown in  FIG. 4D ) over the formed aluminum contacts and interconnect lines to provide electrical contact thereto. As shown in  FIG. 4E , after the silicon nitride layer  204  has been patterned, a metal layer  406 , such as platinum, is deposited over thermal conducting layer  204  using a known technique such as chemical vapor deposition. This deposited layer of platinum  406  is then patterned to form temperature sensor  108 , counter electrode  206 , working electrode  208 , and reference electrode  210 . While the temperature sensor  108 , counter electrode  206 , working electrode  208  and reference electrode  210  can be made from the same metal, it should be understood that this is not required. Temperature sensor  108 , counter electrode  206 , working electrode  208 , and reference electrode  210  can be formed from different materials. 
     As illustrated in  FIG. 4F , after the platinum layer  406  is patterned, a passivation layer  212  of polyimide is formed thereover. Polyimide can be applied by spin coating to form a uniform layer. The deposited polyimide layer is then patterned using known techniques to uncover electrodes  206 ,  208  and  210  and define sensing region  102 . Portions of polyimide layer  212  that are not removed during the patterning step remain over and cover temperature sensor  108 . After the polyimide is patterned, it is cured by heating followed by an oxygen plasma clean to remove organic contaminates. 
     While passivation layer  212  in  FIG. 4G  is illustrated as covering temperature sensor  108 , in other embodiments, passivation layer  212  can be patterned so that sensing region  102  is wider and includes temperature sensor  108 . In other words, in other embodiments, temperature sensor  108  can be exposed in the same way that electrodes  206 ,  208  and  210  are not covered by passivation layer  212  and remain exposed. A sensor in accordance with this embodiment is schematically illustrated in  FIG. 1 . 
       FIG. 5  shows an alternative embodiment of a microsensor  100  wherein thermal energy source  106  and temperature sensor  108  are adjacent to sensing region  102  that includes transducer  104 . In the embodiment illustrated in  FIG. 5 , thermal energy source  106  and temperature sensor  108  are provided below sensing region  102 . The description of thermal energy source  106  and temperature sensor  108  provided above with reference to  FIGS. 1-4  is also applicable to  FIG. 5 . In the embodiment of  FIG. 5 , thermal energy source  106  and temperature sensor  108  are formed on thermal insulating layer  202 . Thermal energy source  106  and temperature sensor  108  are separated from electrodes  104  by a thermal conducting layer  204 . The transducer  104  forming part of sensing region  102  can include electrodes similar to those described above with reference to  FIGS. 1-4 . A portion of transducer  104  is exposed through passivation layer  212 . The portions of passivation layer  212  that remain define the boundaries of sensor region  102 . The semiconductor substrate  200  and thermal insulating layer  202  in  FIG. 5  are described with reference to  FIGS. 1-4  using the same reference numerals. 
       FIG. 6  shows another embodiment of sensor  100  wherein thermal energy source  106  and temperature sensor  108  are provided adjacent to, but not below, electrode component  104 . In the embodiment illustrated in  FIG. 6 , thermal energy source  106 , transducer  104  and temperature sensor  108  are each formed on thermal insulating layer  202 . Passivation layer  212  covers thermal energy source  106  and temperature sensor  108  as well as a portion of transducer  104 . The portion of transducer  104  that is exposed through passivation layer  212  defines sensor region  102 . Other elements common between  FIG. 6  and  FIGS. 1-4  are identified by the same reference numerals. 
       FIG. 7  shows another embodiment of sensor  100  wherein temperature sensor  108  is under transducer  104  and thermal energy source  106 . In the embodiment illustrated in  FIG. 7 , temperature sensor  108  is formed over thermal insulating layer  202 . Over temperature sensor  108  is formed a thermal conducting layer  204 . Thermal energy source  106  and transducer  104  are formed over thermal conducting layer  204 . A portion of transducer  104  and the thermal energy source  106  are covered by passivation layer  212 . The portion of transducer  104  that is not covered by passivation layer  212  remains exposed and defines sensing region  102 . Other elements common between  FIG. 7  and  FIGS. 1-4  are identified by the same reference numerals. 
     Each of the embodiments described by the present disclosure provide localized heating of sensor region  102 . A semiconductor device may include multiple sensor regions  102  and localized heating can be provided to each sensing region and the temperature of each individual sensor region can be sensed and controlled utilizing the subject matter described in the present disclosure. By controlling the temperature of a sensing region through localized heating, variation in measurements resulting from taking multiple measurements at different temperatures can be reduced. In addition, by controlling the temperature of the sensing region, the rate of the interaction occurring in the sensing region, e.g., chemical reaction, can be made to approach the maximum rate which will increase the sensitivity of the microsensor. Increasing the sensitivity of the microsensor is particularly advantageous when the small dimensions of the sensor and/or the small volume of the samples result in small signals. 
     Localized heating produces a substantial difference in the temperature of the sensing region compared to the temperature of the region immediately surrounding the sensing region. For example, in accordance with certain embodiments described herein, the temperature of the sensing region can be increased by 20%, 60%, 100% or any other value compared to the temperature immediately surrounding the sensing region. In some instances, this increase in temperature of the sensing region can translate into the temperature of the sensing region being 10° C., over 20° C., or even greater than the temperature of the region immediately surrounding the sensing region. A temperature of the sensing region is selected which provides improved results at the transducer  104 . 
       FIG. 8  shows a temperature contour image produced using thermal simulation software commercially available from Ansys, Inc. The simulation was based on the thermal energy source illustrated and described with reference  FIG. 2  above. In the simulation, the following parameters were used:
         Substrate was a 525 micrometer silicon die with 1 micrometer silicon dioxide layer;   Thermal energy source  108  was a serpentine tantalum aluminum line 10 micrometers wide and 0.02 micrometer thick having a sheet resistance of the 100 Ohms/square;   Thermal conducting layer was a 0.2 micrometer thick silicon nitride;   Passivation layer was polyimide;   Sensing region  102  formed by the opening in the polyimide layer accounted for 8% of the total die area;   No chemical solution was present in the exposed area;   5 milliamps of current was driven through the tantalum aluminum line.       

     Using these parameters, the simulation predicted an average temperature within the sensing region  102  formed by the opening in the polyimide of 47.5° C. Immediately outside the opening between sensing region  102  and contour line  802 , the predicted temperature dropped to 28.845° C. The simulated temperature between contour lines  804  and  806  was 26.941° C. and the simulated temperature to the exterior of contour line  806  was 26.216° C. This simulation illustrates how the embodiments described herein provide localized heating to a sensor region of a microsensor. 
     In yet another embodiment, electrodes  206 ,  208  and  210  serve as a thermal energy source, a temperature sensor and also as port of the transducer. For example, counter electrode  206  can be cycled through various modes during which in a first mode it participates in the detection of the analyte and in a second mode it serves as a thermal energy source. In this embodiment, counter electrode  206  is formed from a material that allows it to participate in the sensing of the analyte in the sensing region and produce thermal energy when an electric current flows through it. In a similar manner, one of the electrodes  206 ,  208  and  210  can serve as an electrode that participates in the detection of the analyte and also serves as a temperature sensor. In this embodiment, such electrode, such as reference electrode  210  can be coupled to a control unit that cycles the reference electrode  210  through a sensing mode during which it participates in sensing of the analyte and a temperature sensing mode in which it detects the temperature of the sensing region  102 . 
     The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.