Abstract:
Integrated circuit devices include thermal image sensors that utilize quantum dots therein to provide negative resistance characteristics to at least portions of the sensors. The thermal image sensor may include a sensing unit configured to absorb radiation incident on a first surface thereof and first and second electrodes electrically coupled to the sensing unit. The sensing unit includes a plurality of quantum dots therein, which may extend between the first and second electrodes. These quantum dots may be configured to impart a negative resistance characteristic to the sensing unit. In particular, the sensing unit may include a sensing layer having first and second opposing ends, which are electrically coupled to the first and second electrodes, respectively, and the plurality of quantum dots may be distributed within the sensing layer.

Description:
REFERENCE TO PRIORITY APPLICATION 
       [0001]    This application claims priority to Korean Patent Application No. 10-2010-0024412, filed Mar. 18, 2010, the disclosure of which is hereby incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates to integrated circuit devices and, more particularly, to thermal image sensors and related devices. 
       BACKGROUND 
       [0003]    Thermal sensors usually use the change in resistance which occurs when temperature increases with absorbed infrared rays. Thermal sensors require complicated manufacturing processes and high manufacturing costs since temperature coefficient of resistance (TCR) of the material of the thermal image sensors is less than 2 to 3% and a microelectromechanical system (MEMS) structure and high-vacuum packaging are typically needed to obtain necessary sensitivity. Moreover, since the characteristics of the material are fixed, it is difficult to achieve an optimal design for the material according to application of, for example, the range of operating temperature. 
       SUMMARY 
       [0004]    Integrated circuit devices according to embodiments of the invention include thermal image sensors that utilize quantum dots therein to provide, among other things, variable resistance characteristics to at least portions of the sensors. According to some of these embodiments of the invention, a thermal image sensor includes a sensing unit configured to absorb radiation incident on a first surface thereof and first and second electrodes electrically coupled to the sensing unit. The sensing unit includes a plurality of quantum dots therein, which may extend between the first and second electrodes. These quantum dots may be configured to impart a negative resistance characteristic to the sensing unit. In particular, the sensing unit may include a sensing layer having first and second opposing ends, which are electrically coupled to the first and second electrodes, respectively, and the plurality of quantum dots may be distributed within the sensing layer. 
         [0005]    According to additional embodiments of the invention, the sensing layer may include a material selected from a group consisting of amorphous silicon (a-Si) and vanadium oxide (VOx). In particular, the sensing layer may include amorphous silicon and the plurality of quantum dots may be formed of a semiconductor material having a smaller bandgap relative to amorphous silicon. Alternatively, the sensing layer may be a vanadium oxide layer and the plurality of quantum dots may include a metal selected from a group consisting of gold, platinum, copper, chromium and aluminum. Moreover, the plurality of quantum dots may be distributed within the sensing layer and may operate to reduce a resistivity of the sensing layer in response to increases in infrared radiation received at the first surface. 
         [0006]    According to still further embodiments of the invention, the thermal image sensor may include a read-out integrated circuit (ROIC) electrically coupled to the sensing unit. In addition, at least one support may be provided, which is configured to support the sensing unit above a surface of the read-out integrated circuit. A reflective layer may also be provided on the surface of the read-out integrated circuit. This reflective layer is configured to redirect infrared radiation received thereon towards a second surface of the sensing unit, which may extend opposite the first surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0008]      FIG. 1A  is a diagram of an electronic device according to some embodiments of the present invention; 
           [0009]      FIG. 1B  is a sectional view of the electronic device illustrated in  FIG. 1A ; 
           [0010]      FIGS. 2 and 3  are diagrams showing the coulomb blockade of a quantum dot and the conduction and the resistance change with respect to temperature; 
           [0011]      FIG. 4  is a graph of threshold voltage versus temperature; 
           [0012]      FIG. 5  is a diagram of a sensing layer including at least one quantum dot and an electrode connected to the sensing layer; 
           [0013]      FIG. 6  is a graph showing the change in a threshold voltage when the number of quantum dots is changed; 
           [0014]      FIG. 7  is a graph showing two size distributions of quantum dots; 
           [0015]      FIG. 8  is a graph of resistance versus temperature with respect to the two size distributions illustrated in  FIG. 7 ; 
           [0016]      FIGS. 9A and 9B  are sectional views of a thermal image sensor according to some embodiments of the present invention; 
           [0017]      FIG. 10  is a graph showing the change in temperature-resistivity characteristic with respect to a gap between electrodes illustrated in  FIG. 9A ; and 
           [0018]      FIG. 11  is a flowchart of a sensing method of a thermal image sensor according to some embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0019]    The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout. 
         [0020]    It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”. 
         [0021]    It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first signal could be termed a second signal, and, similarly, a second signal could be termed a first signal without departing from the teachings of the disclosure. 
         [0022]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
         [0023]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present application, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0024]      FIGS. 1A and 1B  are diagrams of an electronic device according to some embodiments of the present invention. The electronic device may be a thermal image sensor such as a pyroelectric infrared sensor, a bolometer infrared sensor, or a thermocouple infrared sensor.  FIG. 1A  shows a bolometer unit cell  100  as an example of the electronic device and  FIG. 1B  is a sectional view of the electronic device illustrated in  FIG. 1A , taken along the line a-a′ according to some embodiments of the present invention. 
         [0025]    Referring to  FIGS. 1A and 1B , the bolometer unit cell  100  includes a readout integrated circuit (ROIC)  120 , a support  130 , a pair of electrodes  800 , and a sensing unit  180 . The ROIC  120  includes a reflective layer  170  on the top and is connected to the sensing unit  180  by the support  130 . The support  130  may be conductive. The ROIC  120  may be formed of silicon (Si), silicon oxide, silicon nitride, or metal oxide such as AlO x  or TiO x . 
         [0026]    The sensing unit  180  is supported by the support  130  to be separated (or suspended) by a predetermined air gap from the reflective layer  170  in order to maximize the absorption of incident rays (e.g., infrared rays) and is also positioned between the two electrodes  800 . The sensing unit  180  includes a sensing layer  140 , a first structure layer  151 , a second structure layer  152 , and an absorption layer  160 . The first structure layer  151 , the sensing layer  140 , the second structure layer  152 , and the absorption layer  160  may be sequentially formed from the bottom to the top. 
         [0027]    The absorption layer  160  absorbs incident rays (e.g., infrared rays). The sensing layer  140  senses resistance change and temperature change using the incident rays. The sensing layer  140  may be formed of amorphous silicon (a-Si) or VO x , but the present invention is not restricted thereto. The sensing layer  140  is embedded with at least one quantum dot  110  and senses resistance change and temperature change using the characteristics of the quantum dot  110 . The material of the quantum dot  110  may include at least one among metals such as Au, Pt, Cu, Cr, and Al and narrow-bandgap semiconductor materials. 
         [0028]      FIGS. 2 and 3  are diagrams illustrating the characteristics of the quantum dot  110  according to some embodiments of the present invention.  FIG. 2  is a diagram showing the coulomb blockade of the quantum dot  110  and the conduction with respect to temperature. 
         [0029]    Referring to  FIG. 2 , in order to transmit a carrier through the quantum dot  110 , a coulomb blockade, i.e., energy E 2  that can charge the quantum dot  110  is needed. The energy E 2  is expressed by Equation (1): 
         [0000]    
       
         
           
             
               
                 
                   
                     E 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     
                       e 
                       2 
                     
                     
                       2 
                        
                       C 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where C is a capacitance of the quantum dot  110  and “e” is the quantity of electric charge. 
         [0030]    Also, all particles including the quantum dot  110  have energy E 1  with respect to temperature. The energy E 1  is expressed by Equation (2): 
         [0000]    
       
         
           
             
               
                 
                   
                     E 
                      
                     
                         
                     
                      
                     1 
                   
                   = 
                   
                     
                       3 
                       2 
                     
                      
                     k 
                      
                     
                         
                     
                      
                     T 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where “k” is a Boltzmann constant and T is a transition temperature (or absolute temperature). 
         [0031]    When the carrier is thermally excited by temperature and reaches at least a certain temperature, the energy E 1  may become higher than the energy E 2  (see the arrows in  FIG. 2 ) and a nonconductor may transition to a conductor. As a result, resistance may be changed. 
         [0032]      FIG. 3  is a graph showing the resistance change with respect to temperature. Referring to  FIG. 3 , the energy E 1  is higher than the energy E 2  at high temperature and the graph  31  is obtained. The energy E 1  is higher than the energy E 2  only when at least certain voltage (e.g., a threshold voltage Vth) is applied at low temperature and the graph  32  is obtained. Since the graphs  31  and  32  have different shapes with respect to temperature in a first section D 1 , the first section D 1  (e.g., resistance change in the first section D 1 ) may be used for a thermal image sensor. 
         [0033]      FIG. 4  is a graph of threshold voltage versus temperature. Referring to  FIG. 4 , the threshold voltage Vth decreases as temperature increases. Especially, the threshold voltage Vth nearly converges to zero at a temperature of 370 K on the temperature axis, which may show a similar characteristic to the graph  31  illustrated in  FIG. 3 . In other words, it can be inferred that a nonconductor transitions to a conductor without a certain voltage. 
         [0034]      FIGS. 5 and 6  are diagrams showing that the range of the first section D 1  illustrated in  FIG. 3  is changed depending on the number “N” of quantum dots according to some embodiments of the present invention. In detail,  FIG. 5  is a diagram of the sensing layer  140  including at least one quantum dot  110  and a pair of the electrodes  800  connected to the sensing layer  140 .  FIG. 6  is a graph showing the change in the threshold voltage Vth when the number of the at least one quantum dot  110  is changed. 
         [0035]    Referring to  FIGS. 5 and 6 , the sensing layer  140  is positioned between the two electrodes  800 . The range of the first section D 1  illustrated in  FIG. 3  may be changed by changing the number “N” of the at least one quantum dot  110 . For instance, when the number “N” of quantum dots  110  is increased, the threshold voltage Vth is changed so that a second section D 2  is enlarged to a third section D 3 , as shown in  FIG. 6 . As a result, the threshold voltage Vth can be changed by changing the number of quantum dots  110 . 
         [0036]    As the number of the at least one quantum dot  110  increases, the threshold voltage Vth also increases, resulting in the increase of the transition temperature. As the threshold voltage Vth increases, a nonconductor transitions to a conductor. In other words, as the number of the at least one quantum dot  110  increases, a nonconductor transitions to a conductor. 
         [0037]    The quantum dots  110  may be arranged in an N×M matrix where N and M are integers. Although the embodiments illustrated in  FIG. 5  shows that the change from the threshold voltage Vth to N times the threshold voltage Vth (i.e., N*Vth) by the integer N leads to the change from the second section D 2  to the third section D 3  (or the change from the second section D 2  to the third section D 3  is influenced by N), the present invention is not restricted to these embodiments. For instance, the change from the second section D 2  to the third section D 3  may be influenced by M or both N and M. 
         [0038]      FIGS. 7 and 8  are diagrams showing that temperature-resistance characteristics changes depending on the size of a quantum dot according to some embodiments of the present invention.  FIG. 7  is a graph showing two size distributions  61  and  62  of quantum dots.  FIG. 8  is a graph of resistance versus temperature with respect to the two size distributions  61  and  62  illustrated in  FIG. 7 . 
         [0039]    Referring to  FIGS. 7 and 8 , the second size distribution  62  is larger than the first size distribution  61  and corresponds to a second temperature-resistance graph  72 . The first size distribution  61  corresponds to a first temperature-resistance graph  71 . The quantum dots in the second size distribution  62  have an average diameter of 1.56 nm and the quantum dots in the first size distribution  61  have an average diameter of 1.22 nm. 
         [0040]    When the average diameter decreases from 1.56 nm to 1.22 nm, that is, when the second temperature-resistance graph  72  changes into to the first temperature-resistance graph  71 , it is seen in  FIG. 8  that the transition temperature at which a nonconductor transitions to a conductor increases from 125 K to 300 K. Since the capacitance of the quantum dot  110  decrease as the average size of the quantum dot  110  decreases, the energy E 2  is increased according to Equation (1), which makes the transition from a nonconductor to a conductor more difficult. 
         [0041]    In addition, when the average diameter decreases from 1.56 nm to 1.22 nm, that is, when the second temperature-resistance graph  72  changes into to the first temperature-resistance graph  71 , a high temperature coefficient of resistance (TCR) of at least 100%/° K can be obtained since a resistance change of at least 5000% occurs at a temperature change of 50° K. In other words, the TCR can be changed depending on the size of the quantum dot  110 . 
         [0042]      FIGS. 9A and 9B  are sectional views of a thermal image sensor according to some additional embodiments of the present invention. The thermal image sensor may include at least one bolometer unit cell  100  illustrated in  FIG. 1A  or may have a similar structure to that of the bolometer unit cell  100  illustrated in  FIG. 1A . 
         [0043]    The thermal image sensor may include a substrate (e.g., the ROIC  120  illustrated in  FIG. 1A ), the support  130 , a plurality of sensing layers  140 , a plurality of pairs of electrodes  800 . The plurality of the sensing layers  140  and the plurality of pairs of the electrodes  800  may share the ROIC  120  or the support  130  with one another or have separate ROICs or supports. 
         [0044]    The vertical sectional view of the thermal image sensor may be the same as the diagram shown in  FIG. 1A . The horizontal sectional view of the thermal image sensor (e.g., the sectional view of the bolometer unit cell  100  horizontally taken long the line a-a′), may be like as shown in  FIG. 9A  or  9 B.  FIG. 10  is a graph of showing the change in temperature-resistivity characteristic with respect to a gap between electrodes  800  illustrated in  FIG. 9A . 
         [0045]    Referring to  FIG. 9A , reference numerals  81 ,  82 ,  83  denote the different structures of a thermal image sensor including the sensing layer  140  including the at least one quantum dot  110  and a pair of the electrodes  800  connected to the sensing layer  140 . When the structure changes from  81  to  82  and  83 , the gap between the electrodes  800  increases. At this time, the gap between the electrodes  800  may increase or decrease as the number of the at least one quantum dot  110  increases or decreases, but the present invention is not restricted thereto. For instance, even when the number of the at least one quantum dot  110  is fixed or decreases, the gap between the electrodes  800  may increase. 
         [0046]    Like a case where the number of the at least one quantum dot  110  increases, when the gap between the electrodes  800  increases, the threshold voltage Vth also increases; which increases the transition temperature. As the threshold voltage Vth increases, a nonconductor transitions to a conductor. In other words, as the gap between the electrodes  800  increases, a nonconductor transitions to a conductor. 
         [0047]    The structures  81 ,  82 , and  83  illustrated in  FIG. 9A  respectively correspond to temperature-resistivity graphs  91 ,  92 , and  93  illustrated in  FIG. 10 . Referring to  FIG. 10 , as the temperature increases, the resistivity decreases. This exhibits a negative temperature coefficient (NTC) characteristic of normal oxide semiconductor. 
         [0048]    As described above, a temperature-resistivity graph can be changed depending on the gap between the electrodes  800 . Accordingly, when an electronic device having the structures  81  through  83  having different gaps between the electrodes  800  is used to enable the transition to be made sequentially according to temperature, a thermal image sensor having high sensitivity in a wide range of temperature can be implemented. 
         [0049]    Similarly, when an electronic device having structures  811 ,  812 , and  813  illustrated in  FIG. 9B , in each of which the sensing layer  140  includes a quantum dot  110  having a different size (e.g., a different average size) between two electrodes  800 , is used to enable the transition to be made sequentially according to temperature, a thermal image sensor having high sensitivity in a wide range of temperature can be implemented. Consequently, the transition temperature can be adjusted by changing the number of the at least one quantum dot  110 , the gap between two electrodes  800 , or the size of the at least one quantum dot  110 . 
         [0050]    With the above-described characteristics, the present invention can be widely used for applications needing temperature sensing and adjustment. For instance, the present invention can be used for uncooled thermal image sensor and durable goods used in refrigerators, air conditioners, and automobiles and for the control of temperature of buildings. In addition, the present invention can be used in controlling temperature in the field of industry such as process control. 
         [0051]      FIG. 11  is a flowchart of a sensing method of a thermal image sensor according to some embodiments of the present invention. The sensing method may be performed by a thermal image sensor including the electronic device  100  illustrated in  FIG. 1A . Referring to  FIG. 11 , a sensing unit is suspended above a substrate in operation S 100 . At this time, the substrate may be the ROIC  120 , which may be formed of silicon, silicon oxide, silicon nitride, or metal oxide such as AlO x  or TiO x . At least one quantum dot is embedded in the sensing unit in operation S 200 . At this time, the material of the quantum dot may include at least one among metals such as Au, Pt, Cu, Cr, and Al and narrow-bandgap semiconductor materials. Thereafter, when rays (e.g., infrared rays) are received, temperature change and resistance change are sensed using the characteristics of the quantum dot in operation S 300 . At this time, one of the characteristics of the quantum dot is that the quantum dot transitions from a nonconductor into a conductor when the energy of the quantum dot is higher than the energy of a coulomb blockade at a certain or higher temperature. 
         [0052]    As described above, according to some embodiments of the present invention, an electronic device and a thermal image sensor can be provided with wanted sensitivity without requiring complicated microelectromechanical system (MEMS) structure and high-vacuum packaging, so that manufacturing processes become simple and manufacturing cost is decreased. In addition, the electronic device and the thermal image sensor can have high TCR through the characteristics of a quantum dot. 
         [0053]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in forms and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.