Abstract:
A compact resistive thermal sensor is provided for an integrated circuit (IC), wherein different sensor components are placed on different layers of the IC. This allows the lateral area needed for the sensor resistance wire on any particular IC layer to be selectively reduced. In a useful embodiment, a plurality of first linear conductive members are positioned in a first IC layer, in spaced-apart parallel relationship with one another. A plurality of second linear conductive members are similarly positioned in a second IC layer in spaced-apart parallel relationship with one another, and in orthogonal relationship with the first linear members or in parallel with existing wiring channels of the second IC layer. Conductive elements respectively connect the first linear members into a first conductive path, and the second linear members into a second conductive path. A third conductive element extending between the first and second layers connects the first and second conductive paths into a single continuous conductive path, wherein the path has a resistance that varies with temperature. A device responsive to an electric current sent through the continuous path determines temperature of the path from the path resistance. Two or more of the thermal sensors could be connected in series, for use in measuring critical IC circuits.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention disclosed and claimed herein generally pertains to a compact thermal sensor apparatus for monitoring temperature in an integrated circuit (IC) or other semiconductor package. More particularly, the invention pertains to sensor apparatus of the above type that comprises two or more components, wherein each component is located on a different layer of the IC. Even more particularly, the invention pertains to a sensor apparatus of the above type wherein wiring channels for IC functions unrelated to the thermal sensor can readily be routed through any of the sensor components.  
         [0003]     2. Description of the Related Art  
         [0004]     It is generally important to monitor the internal temperature of an integrated circuit such as a microprocessor or the like. Typically, an analog thermal sensor for integrated circuits comprises a metal line or wire of substantial length and a fixed width. From the designed length of the sensor wire and the resistivity of the material used therefor, the over-all resistance of the sensor wire can easily be measured, by passing a known current through the wire and measuring the voltage thereof. Moreover, a material is selected for the sensor wire that has a resistance which will change as a linear function of temperature, over a specified temperature range. From the linear relationship between resistance and temperature, it is comparatively easy to determine temperature proximate to the sensor from the measured sensor resistance, and also to predict other corresponding values of resistance to temperature. The accuracy and sensitivity of the temperature measurement is determined primarily by the physical properties of the metal used for the sensor wire, and by the cross-section and length of the wire sensor. Variations in the cross-section of the sensor wire are dictated by variations in the wire fabricating process.  
         [0005]     In the past, a wire thermal sensor of the above type has generally been constructed by placing the entire wire on a single metal layer or level of an IC, in a serpentine pattern or configuration. ESD diodes are placed at either end of the sensor wire, to protect the IC semiconductor from high voltage transients. Such prior art arrangement is shown in  FIG. 1 , as described hereinafter. However, this arrangement has a number of drawbacks. The long length of the serpentine line, when constructed on only a single layer of the IC, causes a large amount of the layer area to be used for the sensor circuit. Thus, the sensor configuration can significantly reduce the wiring channels on that layer and hence, the sensor cannot be an integral part of a circuit being measured.  
         [0006]     Moreover, it would often be useful to be able to position a temperature sensor at any desired location in an IC. For example, there could be concern of a hot spot developing at a particular IC location, due to substantial power dissipation. However, because of the limitations of currently available sensors, it could be difficult to place one of such sensors at the particular location, in order to monitor location temperature.  
         [0007]     In a prior art thermal sensor of the above type, there are conflicting requirements in that the sensor wire needs to be narrow enough to provide enough resistance over-all, but must still be wide enough that the sensor itself does not generate heat. Also, the use of narrow width lines or wires makes the sensor more susceptible to variations in the wire fabrication process, since process variations tend to vary by some percentage around a mean value. Presently, there is an optimum range of resistance for a sensor of this type. If the value is too high, the value cannot be measured by available measurement tools. If the resistance is too low, it becomes too insensitive. Process variations limit how close the design can be made to the high side of the optimum resistance range.  
         [0008]     It would be desirable to provide a thermal sensor for integrated circuits that could overcome the above problems and disadvantages found in the prior art.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention is directed to a compact thermal sensor for an integrated circuit or other multi-layered structure, as described hereinafter, wherein prior art problems of the above type are overcome by placing different components of the sensor on two or more different metal layers of the IC or other structure. This allows the lateral area needed for the sensor resistance wire on any particular layer to be selectively reduced. Moreover, other wires not related to the sensor are allowed to pass through the sensor component on a given IC layer, and such wires can be shielded laterally. Thus, the above configuration provides a thermal sensor for an IC that significantly increases utility of space in the IC.  
         [0010]     In one useful embodiment of the invention, a first conductive trace is located in a first metal layer within a plurality of layers. A second conductive trace is located in a second metal layer within the plurality of layers, wherein at least one non-conductive layer in the plurality of layers is located between the first metal layer and the second metal layer. An electrical connector is provided to connect the first conductive trace and the second conductive trace to each other, to form the thermal sensor.  
         [0011]     In a further embodiment, the first and second conductive traces comprise first and second linear conductive members, respectively. One or more channels are formed in at least one of the first and second layers, each of the channels being placed between linear conductive members of the layer in which the channel is formed, each of the channels being disposed to receive conductors pertaining to functions of an IC or other structure in which the sensor resides. Usefully, at least one of the channels is disposed to receive conductors that comprise one or more wires for carrying information, and one or more additional wires for shielding the information carrying wires. In a useful arrangement, a plurality of second linear conductive members are aligned in orthogonal relationship with the first linear conductive members.  
         [0012]     In another useful arrangement, the electrical connector comprises first and second conductive elements, wherein each first conductive element comprises a first end connector located in the second layer and two associated via links. Similarly, each second conductive element comprises a second end connector located in the first layer and two associated via links.  
         [0013]     In yet another embodiment, each of the first end connectors is placed into one of two arrays located in the second layer, wherein the second linear members are respectively located between the two arrays of first end connectors. In like manner, each of the second end connectors is placed into one of two arrays located in the first layer, the first linear members being respectively located between the two arrays of second end connectors. The thermal sensor may usefully be connected in series with one or more sensor circuits that are each substantially similar to the thermal sensor, in order to enable temperature of critical circuits of an associated structure to be measured. The thermal sensor may also have a resistance that varies linearly with variation of an adjacent temperature, over a specified temperature range.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an overhead view showing a prior art thermal sensor for an IC.  
         [0015]      FIG. 2  is a schematic diagram showing a circuit using the prior art thermal sensor of  FIG. 1 .  
         [0016]      FIGS. 3 and 4  are overhead views respectively showing components for an embodiment of the invention, wherein each component lies in a different metal layer of an integrated circuit (IC).  
         [0017]      FIG. 5  is an overhead view showing the components of  FIGS. 3 and 4  combined to form a complete thermal sensor in accordance with an embodiment of the invention, wherein the IC layers between the components have been removed.  
         [0018]      FIG. 6  is an end view taken along lines  6 - 6  of  FIG. 5 , with the IC layers between the components inserted.  
         [0019]      FIG. 7  is an overhead view showing the component of  FIG. 3  together with a conductor channel and conductors that are unrelated to the thermal sensor of  FIG. 5 .  
         [0020]      FIG. 8  is a circuit diagram showing an embodiment of the invention in a generalized form.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     Referring to  FIG. 1 , there is shown a prior art resistive thermal sensor of the type described above, formed on a metal layer  102  of an IC semiconductor that is not otherwise shown. Sensor  100  comprises a continuous wire or line  104  formed of conductive metal. Herein, the terms “wire”, “line” and “trace” are used interchangeably, to refer to a narrow conductive path formed on one of the metal layers of an IC.  
         [0022]     As discussed above, wire  104  must be of substantial length in order to have a resistance that is high enough to be useful in determining temperature adjacent to sensor  100 . Thus, in order to provide sufficient wire length, wire  104  is placed on layer  102  in a serpentine pattern, as shown by  FIG. 1  and discussed above. The pattern comprises several larger loops  104   a ,  104   b  and  104   c , wherein each of the larger wire loops comprises a number of smaller or tighter wire loops  104   d . As stated above, sensor wire  104  must be narrow enough to have sufficient resistance over its length, but must also be wide enough that it is not heated by the current it is carrying. Temperature measurements would, of course, be distorted if operation of the thermal sensor added heat to the IC being monitored.  
         [0023]      FIG. 1  further shows the wire  104  having input and output ends, which are respectively connected through input and output pads  106  and  108  to electrostatic (ESD) diodes  110  and  112  to protect the IC from high voltage transients. It can readily be appreciated from  FIG. 1  how the serpentine arrangement of  FIG. 1  tends to act as a barrier in preventing conductors or conductive paths associated with other circuits of the IC from being placed across layer  102 . Such conductors may have to be routed to other layers, in order to get around the prior art thermal sensor  100 .  
         [0024]      FIG. 2  shows diodes  110  and  112  for thermal sensor  100  connected between a voltage source (V dd ) and a ground connection (G nd ).  
         [0025]     Referring to  FIG. 3 , there is shown a resistor component  300  for a thermal sensor, wherein the component  300  is formed in accordance with an embodiment of the invention on a metal layer  302  of an integrated circuit (IC). Layer  302 , for example, may comprise the M 2  layer of the associated IC.  
         [0026]     Similarly,  FIG. 4  shows a resistor component  400  for the thermal sensor formed on a metal layer  402  of the same IC. Layer  402  may comprise the M 3  layer of the IC, so that it is the next metal layer of the IC below the M 2  layer  302 . A layer of non-conductive material, such as quartz or a selected oxide, is located between the metal layers M 2  and M 3 . As described hereinafter, resistor components  300  and  400  are joined together to form a complete resistive thermal sensor comprising an embodiment of the invention, for use with the associated IC.  
         [0027]     For purposes of illustration, the embodiment of the invention disclosed herein is shown for use with an integrated circuit. However, it is to be emphasized that the invention is by no means limited to such use. To the contrary, it is anticipated that embodiments of the invention can be used for thermal sensing in virtually any type of layered or multi-layered structure that comprises alternating conductive and non-conductive layers. In addition to integrated circuits, such structures can include, without limitation, substrate modules, layered chip carriers, cards and printed circuit boards.  
         [0028]     Referring again to  FIG. 3 , there is shown resistor component  300  comprising a number of narrow linear wires or traces  304   a - k , each formed of an electrically conducting material such as M 2  metal. The linear traces are respectively placed on layer  302  so that they are in spaced apart, substantially parallel relationship with one another.  FIG. 3  shows eleven traces  304   a - k  for purposes of illustration, but other embodiments of the invention may use different numbers of such traces.  
         [0029]      FIG. 3  further shows an input link  306  formed on M 2  layer  302 , input  306  being connected to an end of linear trace  304   a . Each of the other ends of traces  304   a - k  is connected to either a via link  308   a  or  308   b . The via links are made by forming small holes in the IC that extend downward from M 2  layer  302  to the M 3  layer  402 , so that the holes traverse the non-conductive layer between M 2  and M 3 . Each such hole is filled with a conductive material, to form a via link  308   a  or  308   b.    
         [0030]     Referring further to  FIG. 3 , there are shown sets of end connectors  310   a  and  310   b  respectively formed on M 2  metal layer  302 . Each of the end connectors  310   a  and  310   b  comprises a trace of conductive material of the type used to form linear traces  304   a - k , although each of the connectors  310   a  and  310   b  is substantially wider than the traces  304   a - k . The wider trace is needed to add multiple vias to reduce the resistance between layers. The end connectors  310   a  are respectively positioned in a linear array  312   a , in spaced apart relationship, wherein linear array  312   a  is in parallel relationship with each of the linear traces  304   a - k . The connectors  310   b  are similarly positioned in a linear array  312   b , which is in parallel relationship with traces  304   a - k  and linear array  312   a .  FIG. 3  shows each of the linear traces  304   a - k  positioned between the arrays  312   a  and  312   b . The functions of end connectors  310   a  and  310   b  and of via links  308   a  and  308   b  are described hereinafter.  
         [0031]     Resistor component  400  shown in  FIG. 4  is generally very similar to resistor component  300  described above. Thus, component  400  includes linear traces  404   a - k  in parallel spaced-apart relationship with one another, each trace  404   a - k  being substantially identical to a trace  304   a - k  of component  300 . Moreover, resistor component  400  is formed on M 3  metal layer  402  so that elements thereof lie directly beneath elements of resistor component  300 . This allows certain elements of components  300  and  400  to mate or be joined with one another, as described hereinafter. It is to be understood, however, that respective linear traces  404   a - k  are placed on M 3  layer  402  so that they are each oriented in orthogonal relationship with each of the traces  304   a - k  on M 2  layer  302 .  
         [0032]     It is to be understood further that in other embodiments of the invention the traces  404   a - k  may have a different orientation with respect to traces  304   a - k . For example, the traces  404   a - k  could be in parallel relationship with traces  304   a - k , or could lie at any specified angle thereto.  
         [0033]     Referring further to  FIG. 4 , there is shown an output link  406  formed on M 3  layer  402  that is connected to an end of linear trace  404   a . Each of the other ends of traces  404   a - k  is connected to a via link  408   a  or  408   b , which are both similar or identical to via links  308   a  and  308   b  described above. Accordingly, each via link  408   a  and  408   b  comprises a small amount of conductive material that fills a hole extending from layer  402  upward to layer  302 . More particularly, two via links  408   a , from two adjacent traces  404   a - k , extend upward from layer  402  into electrical contact with each of the end connectors  310   a . For example, the via links  408   a  extending from traces  404   b  and  404   c  are both in contact with the uppermost end connector  310   a  of array  312   a , as viewed in  FIG. 3 . Thus, linear traces  404   b  and  404   c  are connected together at their leftward ends, as viewed in  FIG. 4 . Similarly, the via links  408   b  of linear traces  404   a  and  404   b  are both in contact with the uppermost end connector  310   b  of array  312   b , as viewed in  FIG. 3 . The traces  404   a  and  404   b  are thereby connected together at their rightward ends, as viewed in  FIG. 4 . Generally, the via links  408   a  and  408   b  and end connectors  310   a  and  310   b  collectively act to join linear traces  404   a - k  into a continuous electrical path, extending from output link  406  to the end connector  310   b  that is connected to the rightward end of linear trace  404   k , as viewed in  FIG. 4 . Such end connector is more specifically referenced in  FIG. 3  as end connector  310   b ′, to enhance recognition.  
         [0034]      FIG. 4  further shows sets of end connectors  410   a  and  410   b  respectively formed on M 3  metal layer  402 . The end connectors  410   a  and  410   b  are very similar in construction and operation to end connectors  310   a  and  310   b  described above. Connectors  410   a  and  410   b  are positioned in linear arrays  412   a  and  412   b , respectively. The arrays  412   a  and  412   b  are in parallel spaced-apart relationship with the linear traces  404   a - k , which are positioned between the two arrays  412   a  and  412   b.    
         [0035]     It is to be understood that each of the end connector links  410   a  is positioned to engage two of the via links  308   a  extending downward from the M 2  layer, as described above, to establish electrical contact therewith. For example, the via links  308   a  of linear traces  304   b  and  304   c  are both in contact with the leftmost end connector  410   a  of array  412   a , as viewed in  FIG. 4 . Thus, linear traces  304   b  and  304   c  are connected together at their upper ends, as viewed in  FIG. 3 . Similarly, the via links  308   b  of linear traces  304   a  and  304   b  are both in contact with the leftmost end connector link  410   b  of array  412   b , as viewed in  FIG. 4 . The traces  304   a  and  304   b  are thereby connected together at their lower ends, as viewed in  FIG. 3 . More generally, the via links  308   a  and  308   b  and end connectors  410   a  and  410   b  collectively act to join linear traces  304   a - k  into a continuous electrical path, extending from input link  306  to the end connector  410   b  that is connected to the lower end of trace  304   k , as viewed in  FIG. 3 . Such end connector is more specifically referenced in  FIG. 4  as  410   b ′, to enhance recognition.  
         [0036]     Referring to  FIG. 5 , there is shown resistor component  300  positioned over component  400 , with the M 2  layer  302  and nonconductive layer removed. Thus,  FIG. 5  shows the continuous electrical path of resistor component  300 , extending from input link  306  to end connector  410   b ′, together with the continuous electrical path of resistor component  400 , extending from end connector  310   b ′ to output link  406 . It will be seen that the two components  300  and  400  can be readily joined to form a single conductive path having a resistance, by providing an electrical connection between end connectors  310   b ′ and  410   b′.    
         [0037]      FIG. 6  shows a via link  602  extending between end connector  310   b ′ in layer  302  and end connector  410   b ′ in layer  402 , in order to establish the desired connection. Via link  602  is substantially identical to via links  308   a  and  308   b  and  408   a  and  408   b , described above.  FIG. 6  is a side view of the resistor components  300  and  400  shown in  FIG. 5 , wherein M 2  layer  302  and nonconductive layer  604  are inserted between the two components. Accordingly, via link  602  is seen to extend through such layers, between end connectors  310   b ′ and  410   b′.    
         [0038]      FIG. 6  further shows linear traces  304   a - k , connected to respective end connectors  410   b  by means of via link  308   b .  FIG. 6  depicts trace  404   k  connected to an end connector  310   a  through a via link  408   a , and also shows input link  306  and output link  406 .  
         [0039]     Referring to  FIG. 7 , there is shown sensor resistance component  300  as described above, wherein a linear channel  702  has been formed in M 2  layer  302 . More particularly, channel  702  has been formed between linear traces  304   h  and  304   i , in parallel relationship therewith. Channel  702  provides a passage for a wire or conductive trace  704  that is connected to carry signal information for an IC circuit or function, wherein the circuit or function is unrelated to the thermal sensor of component  300 .  FIG. 7  further shows shield wires  706  contained in the channel  702 , to shield wire  704  from surrounding interference. Thus,  FIG. 7  illustrates a significant advantage of the invention, in that embodiments thereof may be readily adapted to avoid blocking signal paths and the routing of information needed for other IC operations.  
         [0040]     Referring to  FIG. 8 , there is shown a generalized embodiment of the invention. As described above, resistor components such as  300  and  400 , on layers M 2  and M 3 , respectively, may be joined together to form a complete thermal sensor. In addition, other resistor components for the sensor, such as components  802 - 806 , may be located on other layers of the multi-layered IC and be interconnected serially with components  300  and  400 . In one arrangement, the components placed on n metal layers could alternate between resistor components such as  300 , and orthogonal resistor components such as  400 . In an alternative arrangement, the resistor components on adjacent layers could have linear traces that were aligned in parallel relationship or at any selected angle with each other, rather than in orthogonal relationship. In yet other arrangements, different layers could have resistors with different numbers of linear traces, or could have different spacing between traces.  
         [0041]     Thus, embodiments of the invention may be readily adapted to meet varying requirements. For example, for the same value of resistance, the sensor wire can be made longer and wider, thus making the sensor wire less susceptible to self heating. Since wiring channels are no longer blocked, the sensor circuit can be integrated with one or more similar temperature-sensitive macros that are daisy-chained together, or connected in series, so that the temperature of critical circuits can be measured. Since utilization of metal might be more intense on one layer than another, the thermal sensor of the invention could be adapted to avoid use of the highly utilized layers, without impacting the links of the over-all sensor resistor.  
         [0042]     Referring further to  FIG. 8 , there are shown additional elements for the circuit of the generalized thermal sensor embodiment. ESD diodes  808  and  810  are connected to the sensor input and output, respectively. The diodes  808  and  810  are respectively coupled between a voltage source (V dd ) and ground (G nd ).  
         [0043]     The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.