Fet operational temperature determination by gate structure resistance thermometry

Abstract

Thermally-sensitive structures and methods for sensing the temperature in a region of a FET during device operation are described. The region may be at or near a region of highest temperature achieved in the FET. Metal resistance thermometry (MRT) can be implemented with gate or source structures to evaluate the temperature of the FET.

What is claimed is: 
     
         1 . A field-effect transistor with temperature sensing comprising:
 a gate;   a floating gate plate adjacent to the gate and having an extended length;   a source contact;   a drain contact;   a first pair of contact tabs connected to the floating gate plate and separated by a first distance for applying a probe current through the floating gate plate; and   a second pair of contact tabs connected to the floating gate plate and separated by a second distance for sensing a voltage across a region of the floating gate plate through which the probe current flows.   
     
     
         2 . The field-effect transistor of  claim 1 , wherein the floating gate plate overlays at least a portion of the gate. 
     
     
         3 . The field-effect transistor of  claim 1 , wherein the floating gate plate exhibits a change in resistance with a change in temperature of the floating gate plate that is not less than 0.001 ohms/°C. 
     
     
         4 . The field-effect transistor of  claim 1 , wherein the first pair of contact tabs comprises a first thin-film resistor and a second thin-film resistor. 
     
     
         5 . The field-effect transistor of  claim 4 , wherein a resistance of the first thin-film resistor and of the second thin-film resistor is not less than 300 ohms. 
     
     
         6 . The field-effect transistor of  claim 4 , wherein the second pair of contact tabs comprises a third thin-film resistor and a fourth thin-film resistor. 
     
     
         7 . The field-effect transistor of  claim 6 , wherein a resistance of the third thin-film resistor and of the fourth thin-film resistor is not less than 300 ohms. 
     
     
         8 . The field-effect transistor of  claim 1 , further comprising a source of the probe current connected to the first pair of contact tabs. 
     
     
         9 . The field-effect transistor of  claim 8 , wherein the source of the probe current is configured to provide alternating current. 
     
     
         10 . The field-effect transistor of  claim 8 , wherein the alternating current has a frequency between 50 kilohertz and 5 megahertz. 
     
     
         11 . The field-effect transistor of  claim 1 , further comprising voltage-sensing circuitry connected to the second pair of contact tabs. 
     
     
         12 . The field-effect transistor of  claim 11 , wherein the voltage-sensing circuit provides an output signal to a feedback circuit that controls a power level of the field-effect transistor. 
     
     
         13 . The field-effect transistor of  claim 1 , wherein the field-effect transistor is incorporated in a power amplifier configured to amplify signals to a power level of not less than 0.25 Watt. 
     
     
         14 . The field-effect transistor of  claim 1 , further comprising an active area controlled by the gate, wherein the active area comprises GaN, GaAs, or InP. 
     
     
         15 . The field-effect transistor of  claim 1 , further comprising an active area controlled by the gate, wherein the active area comprises Si. 
     
     
         16 . The field-effect transistor of  claim 1 , wherein the field-effect transistor is an LDMOS FET, MOSFET, MISFET, or MODFET. 
     
     
         17 . The field-effect transistor of  claim 1 , wherein the field-effect transistor is an HEMT, HFET, or pHEMT. 
     
     
         18 . A method of operating a field-effect transistor, the method comprising:
 applying a signal to a gate of the field-effect transistor;   amplifying the signal with the field-effect transistor;   applying a probe current along a region of a floating gate plate of the field-effect transistor, wherein the floating gate plate overlays at least a portion of the gate; and   sensing a voltage produced by the probe current.   
     
     
         19 . The method of  claim 18 , further comprising evaluating from the sensed voltage a peak temperature of the field-effect transistor. 
     
     
         20 . The method of  claim 19 , wherein the evaluating comprises using calibration results relevant to the field-effect transistor. 
     
     
         21 . The method of  claim 18 , further comprising:
 comparing the sensed voltage to a reference value; and   controlling a power level of the field-effect transistor based upon the comparison.   
     
     
         22 . The method of  claim 18 , wherein applying the probe current comprises applying the probe current along a region of the floating gate plate that overlays at least a portion of the gate. 
     
     
         23 . The method of  claim 18 , wherein applying the probe current comprises applying an alternating current to the region. 
     
     
         24 . The method of  claim 23 , wherein applying the alternating current comprises applying the alternating current at a first frequency that is different from a carrier wave frequency of the signal amplified by the field-effect transistor by not less than a factor of 10. 
     
     
         25 . The method of  claim 18 , wherein applying the probe current comprises intermittently applying the probe current to the region, such that the probe current is driven for intervals of time that are spaced apart by other intervals of time in which no probe current is driven in the region of the floating gate plate. 
     
     
         26 . A field-effect transistor with temperature sensing comprising:
 a gate metal having an extended length with a first end and an opposing second end;   a source contact;   a drain contact;   a first contact tab connected to the gate metal near the first end for applying an alternating probe current to the gate metal;   a capacitor and resistor connected in series between a reference potential and an end region of the gate metal that is remote from the first end; and   a pair of contact tabs connected to separated regions of the gate metal for sensing a voltage drop along the gate metal in response to the alternating probe current.   
     
     
         27 . The field-effect transistor of  claim 26 , wherein the gate metal exhibits a change in resistance with a change in temperature of the gate metal that is not less than 0.001 ohms/° C. 
     
     
         28 . The field-effect transistor of  claim 26 , further comprising a source of the probe current connected to the first contact tab. 
     
     
         29 . The field-effect transistor of  claim 28 , wherein the alternating probe current has a frequency between 50 kilohertz and 5 megahertz. 
     
     
         30 . The field-effect transistor of  claim 26 , further comprising voltage-sensing circuitry connected to the pair of contact tabs. 
     
     
         31 . The field-effect transistor of  claim 30 , wherein the voltage-sensing circuit provides an output signal to a feedback circuit that controls a power level of the field-effect transistor. 
     
     
         32 . The field-effect transistor of  claim 26 , wherein the field-effect transistor is incorporated in a power amplifier configured to amplify signals to a power level of not less than 0.25 Watt. 
     
     
         33 . The field-effect transistor of  claim 26 , further comprising an active area controlled by the gate metal, wherein the active area comprises GaN, GaAs, or InP. 
     
     
         34 . The field-effect transistor of  claim 26 , further comprising an active area controlled by the gate metal, wherein the active area comprises Si. 
     
     
         35 . The field-effect transistor of  claim 26 , wherein the field-effect transistor is an LDMOS FET, MOSFET, MISFET, or MODFET. 
     
     
         36 . The field-effect transistor of  claim 26 , wherein the field-effect transistor is an HEMT, HFET, or pHEMT. 
     
     
         37 . A method of operating a field-effect transistor, the method comprising:
 applying a signal to a gate metal of the field-effect transistor;   amplifying the signal with the field-effect transistor;   applying an alternating probe current to a first end region of the gate metal of the field-effect transistor, wherein a second end region of the gate metal is remote from the first end region and is terminated by a capacitor and resistor connected in series between a reference potential and the second end region; and   sensing a voltage drop produced along a length of the gate metal by the alternating probe current.   
     
     
         38 . The method of  claim 37 , further comprising evaluating from the sensed voltage a peak temperature of the field-effect transistor. 
     
     
         39 . The method of  claim 37 , further comprising:
 comparing the sensed voltage to a reference value; and   controlling a power level of the field-effect transistor based upon the comparison.   
     
     
         40 . The method of  claim 37 , wherein applying the alternating probe current comprises
 applying the alternating probe current at a first frequency that is different from a carrier wave frequency of the signal by not less than a factor of 10.   
     
     
         41 . The method of  claim 37 , wherein applying the alternating probe current comprises intermittently applying the alternating probe current to the first end region, such that the alternating probe current is driven for intervals of time that are spaced apart by other intervals of time in which no alternating probe current is driven along the length of the gate metal. 
     
     
         42 . A field-effect transistor with temperature sensing comprising:
 a gate metal having an extended length with a first end and a second end;   a source;   a drain; and   a first contact tab connected to a first end region of the gate metal near the first end and configured for applying an alternating probe current to the gate metal, wherein no other contact tab is connected to the gate metal for conducting the probe current and wherein essentially all of the probe current, when applied, couples to a source of the field-effect transistor.   
     
     
         43 . The field-effect transistor of  claim 42 , further comprising a pair of contact tabs connected to separated regions of the gate metal for sensing a voltage drop along the gate metal in response to the alternating probe current. 
     
     
         44 . The field-effect transistor of  claim 43 , further comprising voltage-sensing circuitry connected to the pair of contact tabs. 
     
     
         45 . The field-effect transistor of  claim 44 , wherein the voltage-sensing circuit provides an output signal to a feedback circuit that controls a power level of the field-effect transistor. 
     
     
         46 . The field-effect transistor of  claim 42 , wherein the gate metal exhibits a change in resistance with a change in temperature of the gate metal that is not less than 0.001 ohms/° C. 
     
     
         47 . The field-effect transistor of  claim 42 , wherein the alternating probe current has a frequency between 50 kilohertz and 5 megahertz. 
     
     
         48 . The field-effect transistor of  claim 42 , wherein the field-effect transistor is incorporated in a power amplifier configured to amplify signals to a power level of not less than 0.25 Watt. 
     
     
         49 . The field-effect transistor of  claim 42 , further comprising an active area controlled by the gate metal, wherein the active area comprises GaN, GaAs, or InP. 
     
     
         50 . The field-effect transistor of  claim 42 , further comprising an active area controlled by the gate metal, wherein the active area comprises Si. 
     
     
         51 . The field-effect transistor of  claim 42 , wherein the field-effect transistor is an LDMOS FET, MOSFET, MISFET, or MODFET. 
     
     
         52 . The field-effect transistor of  claim 42 , wherein the field-effect transistor is an HEMT, HFET, or pHEMT. 
     
     
         53 . A method of operating a field-effect transistor, the method comprising:
 applying a signal to a gate metal of the field-effect transistor;   amplifying the signal with the field-effect transistor;   applying an alternating probe current to a region of the gate metal of the field-effect transistor, wherein essentially all of the alternating probe current couples to a source of the field-effect transistor; and   sensing a voltage drop produced along a length of the gate metal by the alternating probe current.   
     
     
         54 . The method of  claim 53 , further comprising evaluating from the sensed voltage a peak temperature of the field-effect transistor. 
     
     
         55 . The method of  claim 53 , further comprising:
 comparing the sensed voltage to a reference value; and   controlling a power level of the field-effect transistor based upon the comparison.   
     
     
         56 . The method of  claim 53 , wherein applying the alternating probe current comprises applying the alternating probe current at a first frequency that is different from a carrier wave frequency of the signal by not less than a factor of 10. 
     
     
         57 . The method of  claim 53 , wherein applying the alternating probe current comprises intermittently applying the alternating probe current to the region, such that the alternating probe current is driven for intervals of time that are spaced apart by other intervals of time in which no alternating probe current is driven in the region of the gate metal.