Abstract:
A temperature monitoring circuit for an integrated circuit on a monolithic chip, the temperature monitoring circuit comprising a temperature sensor disposed on the monolithic chip, a system monitor disposed on the monolithic chip, and electrically conductive traces for electrically connecting the temperature sensor to the system monitor. In this manner, the temperature on the monolithic chip can be monitored by the integrated circuit itself, and appropriate action can be programmed to occur upon attaining various set points or conditions.

Description:
FIELD 
       [0001]    This invention relates to the field of integrated circuits. More particularly, this invention relates to a general method for measuring and capturing multiple on-chip junction temperature and Vdd values and making these values available as state variables as part of a closed loop control system. 
       BACKGROUND 
       [0002]    There is a continual desire to fabricate integrated circuits that are smaller, faster, and consume less power than earlier designs. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices. 
         [0003]    As the size of integrated circuits is reduced, so also are the gate-lengths and other critical dimensions. An undesirable side effect this size reduction is unwanted leakage of current in the transistors that are formed in the integrated circuits, which leakage generally increases the amount of power consumed by the integrated circuit. Further, the excess power consumption also raises the temperature of the semiconducting transistor junction (referred to as the junction temperature, or Tj). 
         [0004]    An elevated junction temperature creates several problems. For example, there is a limit to the amount of power that an integrated circuit of a given size can dissipate in the form of heat. This power dissipation limit constrains the size of the integrated circuit to be no less than that which can dissipate the amount of heat that is generated at the junction. Fabricating the integrated circuit at a smaller size tends to cause a build-up of heat at the junction, which can reduce the reliability of the integrated circuit. In extreme examples, operating the integrated circuit at a higher junction temperature can result in a condition called thermal run-away, which can destroy the integrated circuit. 
         [0005]    What is needed, therefore, is a system that overcomes problems such as those described above, at least in part. 
       SUMMARY 
       [0006]    The above and other needs are met by a temperature monitoring circuit for an integrated circuit on a monolithic chip, the temperature monitoring circuit comprising a temperature sensor disposed on the monolithic chip, a system monitor disposed on the monolithic chip, and electrically conductive traces for electrically connecting the temperature sensor to the system monitor. In this manner, the temperature on the monolithic chip can be monitored by the integrated circuit itself, and appropriate action can be programmed to occur upon attaining various set points or conditions. 
         [0007]    In various embodiments, the temperature sensor comprises a plurality of temperature sensors. In alternate embodiments, the plurality of temperature sensors are either distributed substantially uniformly across the monolithic chip, or are designed concurrently with and incorporated into functional blocks of the integrated circuit, and the placement of the temperature sensors on the monolithic chip is wholly dependent upon the placement of the functional blocks. In alternate embodiments, the electrically conductive traces are wholly contained on the monolithic chip, or are partially formed in a package substrate to which the monolithic chip is physically attached and electrically connected. 
         [0008]    In some embodiments the system monitor is formed in a peripheral portion of the monolithic chip. The system monitor in some embodiments is formed of transistors having a relatively thicker gate oxide in comparison to a relatively thinner gate oxide that is used in transistors formed in a core portion of the integrated circuit. In some embodiments the system monitor is formed of transistors that operate at a relatively higher voltage in comparison to a relatively lower voltage that is used in transistors formed in a core portion of the integrated circuit. 
         [0009]    In some embodiments the system monitor includes a multiplexed analog to digital converter for sensing voltage at the temperature sensor, a current source for providing a current to the temperature sensor, a controller for at least one of controlling operation of the system monitor and manipulating voltage values sensed from the temperature sensor, a first memory for holding programming for the controller, and a second memory for holding the voltage values sensed from the temperature sensor. 
         [0010]    In various embodiments, the temperature sensor is at least one of a temperature dependent diode junction, a bi-metallic junction, and a resistive thermal device. In some embodiments the temperature sensor is two resistors of different resistance in a series, where a current is applied at one end of the series and a voltage is sensed between the two resistors. In another embodiment the temperature sensor includes a first set of two resistors of different resistance one from another in a first series, where a first current is applied at one end of the first series and a first voltage is sensed between the two resistors of the first series, and a second set of two resistors of different resistance one from another in a second series, where a second current is applied at one end of the second series and a second voltage is sensed between the two resistors of the second series. In some embodiments the first current is equal to the second current. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
           [0012]      FIG. 1  is a top plan view of a monolithic integrated circuit according to an embodiment of the present invention, having a monitor block and temperature sensors, connected by electrically conductive traces. 
           [0013]      FIG. 2  is a top plan view of a monolithic integrated circuit according to another embodiment of the present invention, having a monitor block and temperature sensors, connected by electrically conductive traces, and functional blocks. 
           [0014]      FIG. 3  is a functional block diagram of a monitor block according to an embodiment of the present invention. 
           [0015]      FIG. 4  is a side cross sectional view of an integrated circuit electrically connected to a package substrate according to an embodiment of the present invention. 
           [0016]      FIG. 5  is a circuit diagram of a temperature sensor circuit according to an embodiment of the present invention. 
           [0017]      FIG. 6  is a circuit diagram of a temperature sensor circuit according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    In accordance with the various embodiments of the present invention, it is desirable to sense the junction temperature and the integrated circuit power supply voltages, and to use those as input variables to control leakage power with the integrated circuit. Many different methods of controlling leakage power can be used, such as adjusting the back bias to modify the threshold voltage, and deducting Vdd from inactive logic blocks while still retaining state voltage. In its basic embodiments, the invention provides a system monitor block within a monolithic integrated circuit, which system monitor block acts as a central resource that is connected to one or more probe points across the die. 
         [0019]    The first section of this disclosure describes chip level planning for multiple on-die sensors and routing to a controller block. The second section of this disclosure describes in more detail the methods of estimating integrated circuit temperatures. 
       Layout 
       [0020]    With reference now to  FIG. 1 , there is depicted a top plan view of a monolithic integrated circuit  10  according to an embodiment of the present invention, having a monitor block  12  and temperature sensors  14 , connected by electrically conductive traces  16 . In the embodiment of  FIG. 1 , the monitor block  12  is placed in a peripheral portion of the integrated circuit  10 , and the temperature sensors  14  are disposed substantially equidistant one from another across the surface of the integrated circuit  10 , regardless of the placement of other elements of the integrated circuit  10 , which are not depicted in  FIG. 1 . 
         [0021]    In the embodiment of  FIG. 2 , the monitor block  12  is placed in a more central portion of the integrated circuit  10 , and the temperature sensors  14  are integrated into some of the functional blocks  18  of the integrated circuit  10 , and are thus placed in locations of the integrated circuit  10  that are dependant upon the location of the functional blocks  18 , rather than being evenly spaced across the surface of the integrated circuit  10 . Further, in the embodiment of  FIG. 2 , not all of the functional blocks  18  include a temperature sensor  14 . 
         [0022]    For example, some embodiments include a temperature sensor  14  in a complex intellectual property hard macro  18 . This design philosophy generally simplifies the design flow for the insertion of the temperature sensors  14 , and tends to eliminate placement and routing blockages that hinder the timing closure of a given design. Instantiation of the temperature sensor  14  in a given functional block  18  is accomplished by a specialist designer, thus avoiding wide deployment of skills and expertise in placement and hook-up. Instantiation of the functional block  18  with an embedded temperature sensor  14  is done “as usual” by designers who don&#39;t require the special skills and expertise in placement. Because complex functional blocks  18  that require hardening to ensure predictability (such as high speed microprocessors, CAM memory, and large SRAM) are often high performance, these functional blocks  18  are also more likely to draw higher powers, and thus will tend to run hotter. Therefore, this embodiment ensures that these functional blocks  18  include a temperature sensor  14 . 
         [0023]    Some embodiments include more temperature sensors  14  than are depicted in  FIGS. 1 and 2 , and other embodiments include fewer temperature sensors  14  than are depicted in  FIGS. 1 and 2 . Some embodiments strive for a uniform distribution of temperature sensors  14  across the surface of the integrated circuit  10 , with a large enough number of temperature sensors  14  so as to reduce and preferably eliminate local hot spots on a relatively larger chip  10 . The number of such temperature sensors  14  will tend to depend in part upon the physical size of the chip  10 , and the distribution of the temperature sensors  14  might depend in part upon the amount of localized heat that is generated by different functional blocks  18  in different parts of the integrated circuit  10 . 
         [0024]    With reference now to  FIG. 3 , there is depicted a functional block diagram of the monitor block  12 . The integrated circuit system monitor block  12  includes a multiplexed analog to digital converter  28  that makes electrical connections to the temperature sensors  14  through the traces  16 . Current sources  38  also make electrical connections to the temperature sensors  14  through the traces  16 , and provide the current for driving the temperature sensors  14 . In some embodiments the temperature sensors  14  include a diode where the junction voltage is temperature dependent. In other embodiments the temperature sensors  14  include a thermal resistance structure, such as an RTD or a thermocouple. In some embodiments, the temperature at a given location of the integrated circuit  10  can be sensed by reading the local Vdd at a variety of different locations. In one embodiment, the muxed ADC  28  reads the temperature dependent voltages of the temperature sensors  14  and compares the voltages of the temperature sensors  14  against a reference voltage  40 . 
         [0025]    A system interface  34  is provided for access to monitored data  32  via an access protocol  30 . The system interface  34  is routed off of the chip  10 . The access protocol  30  in some embodiments is defined such that the monitor block  12  generates an interrupt to or supplies monitored data in response to read requests from an off-chip controller. A register file or random access memory  26  stores the monitored voltage values from the muxed ADC  28 , for access across the system interface  34 . The derived data values may be stored or computed. A finite state machine  20  or main control unit provides access and update methods for monitored data under the control of a stored program  22 . For example, the finite state machine  20  can provide averaging of successive readings from the muxed ADC, or produce an alarm when a given voltage or other value exceeds a predefined level. 
         [0026]    The monitor block  12  in some embodiments includes an interface  36  to an operational test program, such that system or application specific parameters may optionally be introduced, such as calibration parameters from a die level test, die identification values, alarm threshold values, and code to determine an update sampling frequency. 
         [0027]    The monitor block  12  in one embodiment is implemented in an input/output region of the integrated circuit  10 , and is designed with transistors that have relatively thicker oxide that are capable of operating at 1.5 volts or 1.8 volts, so as to be able to sense the core Vdd of 0.8 volts to 1.2 volts, while still retaining an analog voltage overhead. It is appreciated that as core voltages change in the future, similar changes in the operating voltage of the transistors of the monitor block  12  are also contemplated. Thus, the absolute values of these voltages are specific to current technologies, but the concept that the gate oxide for the monitor block  12  is generally thicker than that used in the core transistors will generally apply. 
         [0028]    In one embodiment, whatever values—such as voltage—that sensed by the sensors  14  is converted to a temperature value in the system monitor block  12 , without having to ship the data off the chip  10  to some other controller or processor. In another embodiment, any values sensed by the sensors  14  are compared to values in the system monitor block  12  that are in the native format of the sensed values—such as voltage—but which have been calibrated to temperature values, and once again the temperature at the temperature sensors  14  can be known without shipping the data off-chip to some other controller or processor. In various embodiments, the system monitor block  12  includes set points in either the program  22  or the memory  26 , and the system monitor block  12  can control various operations of the integrated circuit  10 , again without having to send data off-chip or receiving instructions from off-chip. 
         [0029]    With reference now to  FIG. 4 , there is depicted an embodiment of the integrated circuit  10  in the form of a flip chip, that is connected to a package substrate  42  via bumps  44 . In this embodiment, bump  44   a  is electrically connected to a temperature sensor  14 , such as through a trace  16 , and bump  44   b  is electrically connected to the monitor block  12 , again such as through a trace  16 . The completion of the electrical circuit between the monitor block  12  and the temperature sensor  14  is completed, in this embodiment, through the connector  46  that is disposed within one or more layers of the package substrate  42 . 
         [0030]    Routing the temperature sensor  14  to the system monitor  12  in this embodiment is accomplished by a package designer specialist, and avoids a wide deployment of skills and expertise in routing and hook-up of the temperature sensors  14 . This embodiment can also eliminate on-die  10  routing blockages and matched differential resistance routes, which hinder timing closure of a design when the temperature sensor  14  routing is not on the die  10 . Further, this embodiment can overcome the variability of on-chip  10  route-length resistance and differential resistance, because: (a) the few traces  16  specific to a temperature sensor  14  can be routed continuously in a single package plane in low resistance metal (without via chains); (b) routes  16  for different temperature sensors  14  can be easily matched (if necessary) in resistance to reduce or eliminate effects that might lead to differential junction temperature measurements. Because the temperature sensors  14  and the system monitor  12  are not connected on the die  10  in this embodiment, it is possible at either die test or wafer test to calibrate the temperature sensor  14  independently of the system monitor  12 . This calibration data can then be used to enhance the accuracy of the measurements. 
         [0031]    In another embodiment, if it is desirable to equalize out (1) routing resistance differences between two or more temperatures sensors  14  and the system monitor  12 , or (2) routing resistance differences between two or more connections on the same temperature sensor  14  and the system monitor  12 , then the width of the traces  16 , such as depicted in  FIGS. 1 and 2 , can be adjusted. For example, if one trace  16  has a length of L, with a resistance of R per unit length, then a trace  16  that has a length of 2L can be equalized with a resistance of R/2 per unit length, and so forth. This can be accomplished by adjusting the relative widths of the various traces  16 . However, in some embodiments it is more practical to make these resistance adjustments on electrical connections  46  within the package substrate  42  than it is to make the adjustments in the integrated circuit  10 . 
       Temperature Measurement 
       [0032]    According to the description above, one or more temperature sensors  14 , such as reference resistors, are connected to a system monitor  12 , such as by using connectors  46  that are routed in package substrate  42 . The system monitor  12  current source  38  forces current into the reference resistor  14 . The temperature dependent resistance of the sensor  14  changes as a change in voltage across the resistance. The change in temperature of the sensor  14  can be inferred from measuring the change in voltage. 
         [0033]    In another embodiment there can be implemented in the temperature sensor  14  two co-located resistors having different values, such as R and  11 R, as depicted in  FIG. 5 . The change in voltage at V 1  is measured, which will vary as a function of the temperature of the resistors. In another embodiment there can be implemented in the temperature sensor  14  two sets of two co-located resistors of different values, such as R and  11 R, as depicted in  FIG. 6 . The differential voltage (V 2 −V 1 ) is measured when each set of resistors is driven by matched current sources  38 . 
         [0034]    In another embodiment, one or more reference junctions between dissimilar metals are implemented using traces  46  formed in the package substrate  42 . Package substrates  42  are typically manufactured using electro-chemical plating processes to deposit or remove a metal such as copper on one or more layers used in the build-up. Other metals are commonly used in the manufacture of packages, such as nickel (which may be used as a finish). The substrate  42  manufacturing process is modified in this embodiment to include a plating step on one or more layers, such that a copper-nickel junction is formed (for example—other suitable metal combinations are possible). The junction is formed in the substrate  42  at a location under the die  10 , such as indicated at  48  in  FIG. 4 . The terminals of the junction  48  are connected to the on-chip system monitor  12 , such as through the traces  46  and bumps  44 . 
         [0035]    Thermoelectric junctions can also be formed in the temperature sensors  14  on the chip  10 , between two dissimilar metals that are used to form portions of the traces  16 . For example, in a first step, the first terminal in the sensor  14  can be formed in a metal-1 layer with either an additive or a subtractive process. The second terminal in the sensor  14  can then be formed in a second step, by over-plating metal-1 with metal-2, again in either an additive or subtractive process. Thus, the thermoelectric junction in this embodiment is formed using dissimilar metals that are deposited on the chip  10 , rather than in or on the package substrate  42 . In some embodiments the junction does not form a part of the “main” circuit of the integrated circuit  10 . The sensors  14  of these embodiments can be connected and routed according to any of the methods described above. 
         [0036]    In another embodiment, the muxed ADC  28  if the system monitor  12  is used to measure a thermoelectric junction potential in the sensor  14 . By measuring a temperature dependent voltage change, a change in temperature can be inferred. The voltage change is compared in one embodiment to a reference voltage, such as a pseudo cold-junction. The reference voltage and junction potential can be calibrated at a known temperature when the integrated circuit  10  is tested. The calibration data that is captured at test time can be programmed into an on-chip nonvolatile memory (such as an eFuse block) for use by the system controller  12 . 
         [0037]    The information from the system monitor  12  can be used as part of a closed loop control system for the integrated circuit  10 . For example, components either inside or outside of the system monitor  12 , or on or off of the chip  10 , can monitor the temperature at different locations on the chip  10 , and can send signals to alerts or alarms in regard to the temperature conditions of the chip  10 . In this manner, the operation of the integrated circuit  10  can be adjusted if the temperature reaches a critical point, where the integrated circuit  10  could be damaged in some manner. 
         [0038]    The foregoing description of preferred embodiments for this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.