Semiconductor device with temperature detecting diode, method of forming the device and temperature detecting method using the device

The object of the present invention is to provide a temperature detecting method wherein a temperature detecting diode is formed in the proximity of and thermally coupled to an object of temperature detection element in the form of a semiconductor element so that, even when a high power is instantaneously applied, the temperature of the object element for temperature detection can be detected with a high degree of accuracy. According to the present invention, in a temperature detecting method for detecting, in a semiconductor device which includes an object element for temperature detection in the form of a semiconductor element and a temperature detecting diode formed in the proximity of the object element for temperature detection, the temperature of the object of temperature detection element from the ambient temperature and heat generated by the element, the temperature detecting diode is formed on the same pellet as that of the element at a position at which more than one half of the circumference thereof is surrounded by the object element for temperature detection.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a temperature detecting method which makes use of 
a forward voltage of a diode, and more particularly to a temperature 
detecting method wherein an object of temperature detection element in the 
form of a semiconductor element and a temperature detecting diode formed 
in the proximity of the object of temperature detection element are 
thermally coupled to detect the temperature of the element by means of the 
temperature detecting diode. 
2. Description of the Related Art 
Conventional temperature detection which makes use of a diode is described 
with reference to FIGS. 1 to 6. 
As a conventional example including a temperature detecting method, a block 
diagram of a semiconductor device of three terminal construction having a 
built-in overheat preventing function is shown in FIG. 1. Object of 
temperature detection element 102 is formed from a bipolar transistor, a 
field effect transistor or a like element and serves as a heat generating 
source. Heat 106 generated from object of temperature detection element 
102 is transmitted to temperature detecting diode D1. Temperature 
detecting diode D1 placed at position p converts a temperature into a 
voltage in accordance with the relationship between temperature T(p) and 
forward voltage VF(p) of the diode illustrated in FIG. 2. 
Overheat protecting circuit 103 obtains voltage VF(p) representative of the 
temperature of object of temperature detection element 102 from 
temperature detecting diode D1 and operates switch SW1 to switch on or off 
in response to the value of voltage VF(p) to control the supplying 
condition of the input voltage to object of temperature detection element 
102 thereby to control the temperature of object element 102. 
A construction of a pellet for realizing the block diagram of FIG. 1 is 
shown in FIGS. 3(a) and 3(b). 
Object element 102 for temperature detection such as a bipolar transistor 
or a field effect transistor and temperature detecting diode D1 are formed 
in a neighboring relationship to each other on silicon substrate 101 by 
diffusion processing. Overheat protecting circuit 103 is formed at a 
location on silicon substrate 101 comparatively far from object of 
temperature detection element 102. Those elements are connected by 
aluminum wiring lines or the like so that they cooperatively form a 
semiconductor device having an overheat preventing function. 
An example of temperature detecting method wherein object of temperature 
detection element 102 and temperature detecting diode D1 are formed in a 
neighboring relationship to each other on the same chip and thermally 
coupled to each other to detect the temperature of object element 102 for 
temperature detection by means of temperature detecting diode D1 in this 
manner is disclosed, for example, in Japanese Patent Laid-Open Application 
No. Heisei 01-196858. This document discloses that a temperature detecting 
circuit which makes use of a forward voltage of a diode is incorporated on 
a pellet on which a driving transistor is mounted, and the driving 
transistor and the temperature detecting diode are individually connected 
to a device. This example is described below. 
FIG. 4 is a schematic view showing a structure of the essential part of 
object element 202 for temperature detection and temperature detecting 
diode D1 disclosed in the document. The example shown in FIG. 4 employs an 
N-channel field effect transistor of the enhancement type. In FIG. 4, a 
portion formed by terminals G, D and S is a field effect transistor 
serving as object element 202 for temperature detection, and another 
portion formed from terminals A and K serves as temperature detecting 
diode D1. 
As described above, conventional temperature detecting diode D1 is formed 
such that it is included in a block adjacent object element 202 for 
temperature detection such as the block of overheat protecting circuit 
203. 
A concrete temperature detecting circuit employing temperature detecting 
diode D1 is shown in FIG. 5. Temperature detecting diode D1 is connected 
in a forward direction, and detecting current of several mA flows through 
temperature detecting diode D1. Voltage VF(p) across temperature detecting 
diode D1 is compared with reference voltage Vref set by resistors R7 and 
R8 by comparator Cmp1, and voltage Vo is outputted from comparator Cmp1. 
An example of temperature detecting circuit of the type described above is 
disclosed in Japanese Patent Laid-Open Application No. Showa 56-120153 or 
Japanese Patent Laid-Open Application No. Heisei 1-114060. 
The temperature detecting circuit disclosed in Japanese Patent Laid-Open 
Application No. Heisei 56-120153 is constructed such that a diode for 
detecting the temperature is disposed adjacent another pellet or the same 
pellet in the proximity of an object element for temperature detection 
such as a transistor or an IC, and a temperature detecting circuit which 
makes use of the forward voltage of the diode is incorporated in the 
outside or the inside of the IC and the forward voltage of the diode 
including the temperature information is compared with a reference voltage 
by a comparator or an operational amplifier to control the current flowing 
through the IC to protect the device. Also overheat protecting circuit 103 
shown in FIG. 1 has a similar construction to that disclosed in Japanese 
Patent Laid-Open Application No. Showa 56-120153. 
The temperature detecting circuit disclosed in Japanese Patent Laid-Open 
Application No. Heisei 1-114060 is constructed such that a temperature 
detecting circuit including a transistor for detecting the temperature is 
disposed in the proximity of an object element for temperature detection 
and makes use of a forward voltage of the diode between the base and the 
emitter of a transistor forming an IC to control the current of a power 
source connected to the IC to protect the device. 
The temperature distribution on the section taken along line Z-Z' of the 
schematic views of FIGS. 3(a) and 3(b) including temperature detecting 
diode D1 immediately after a high power is instantaneously applied to the 
semiconductor device shown in FIGS. 3(a) and 3(b) is such as that shown in 
FIG. 6. 
The temperature distribution on the section taken along line Z-Z' usually 
exhibits the highest temperature (Tmax) at the location of object element 
102 for temperature detection, and the temperature of temperature 
detecting diode D1 spaced by distance p from object of temperature 
detection element 102 is T(p) which is lower than temperature Tmax of 
element 102. 
Where the applied power is represented by P, the maximum temperature of 
element 102 is represented by Tmax and the thermal resistance between 
temperature detecting diode D1 at position p and element 102 is 
represented by Rth(p), temperature T(p) at position p of temperature 
detecting diode D1 in the conventional example is given by following 
equation 1: 
EQU T(p)=Tmax-P.times.Rth(p) equation 1 
Further, when sufficient time elapses after power is applied to the 
semiconductor device, the temperatures of both element 102 and temperature 
detecting diode D1 approach a substantially uniform temperature. 
However, in the prior art described above, as seen from FIGS. 3(a) and 
3(b), a thermal resistance originating from the thermal conductivity 
and/or the distance between object of temperature detection element 102, 
which also serves as a heat generating source, and temperature detecting 
diode D1, and particularly when a high power is instantaneously applied or 
in a like case, a difference arises between temperature Tmax of element 
102 and temperature T(p) of temperature detecting diode D1 as seen in FIG. 
6. Consequently, where the prior art is applied to an overheat protecting 
circuit or a like circuit, there is a problem in that the temperature of 
element 102 may become higher than an overheat protecting temperature set 
in advance by resistance R7 and resistance R8 of the temperature detecting 
circuit of FIG. 5. 
This problem is not significant while the input power to the semiconductor 
is low. However, when a high power is inputted instantaneously, the 
problem becomes significant. Accordingly, not only realization of a 
semiconductor device having an overheat protecting function or a like 
function is difficult, but also there is the possibility that the life of 
the semiconductor device may be reduced by inadvertent application of a 
high power. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the problems of the prior 
art described above, and it is an object of the present invention to 
provide a semiconductor device provided with a temperature detecting diode 
which is improved in accuracy of the detected temperature and has an 
increased life and a forming method for and a temperature detecting method 
of the semiconductor device. 
According to an aspect of the present invention, there is provided a method 
of forming a semiconductor device provided with a temperature detecting 
diode formed in the proximity of an object of temperature detection 
element for detecting a temperature of the element from the ambient 
temperature and heat generated by the element, characterized in that, 
in order to reduce the thermal resistance between the object of temperature 
detection element and the temperature detecting diode, the temperature 
detecting diode is formed on the same pellet as that of the object of 
temperature detection element in such a manner that more than one half of 
the circumference thereof is surrounded by the element. 
According to another aspect of the present invention, there is provided a 
method of forming a semiconductor device provided with a temperature 
detecting diode formed in the proximity of an object of temperature 
detection element for detecting a temperature of the object from the 
ambient temperature and the heat generated by the element, characterized 
in that 
the temperature detecting diode and the object of temperature detection 
element are formed on the same pellet, and a heat conducting member is 
formed on a surface of the pellet including at least some portions of the 
temperature detecting diode and the object of temperature detection 
element and an area interconnecting the temperature detecting diode and 
the object of temperature detection element. 
According to a further aspect of the present invention, there is provided a 
semiconductor device provided with a temperature detecting diode formed in 
the proximity of an object of temperature detection element for detecting 
a temperature of the element from the ambient temperature and heat 
generated by the element, characterized in that, 
in order to reduce the thermal resistance between the object of temperature 
detection element and the temperature detecting diode, the temperature 
detecting diode is formed on the same pellet as that of the object of 
temperature detection element in such a manner that more than one half of 
the circumference thereof is surrounded by the object of temperature 
detection element. 
According to a still further aspect of the present invention, there is 
provided a semiconductor device provided with a temperature detecting 
diode formed in the proximity of an object element for temperature 
detection for detecting a temperature of the object element for 
temperature detection from the ambient temperature and heat generated by 
the object element for temperature detection, characterized in that the 
temperature detecting diode and the object of temperature detection 
element are formed on the same pellet, and a heat conducting member is 
formed on the surface of the pellet including at least some portions of 
the temperature detecting diode and the object of temperature detection 
element and an area interconnecting the temperature detecting diode and 
the object of temperature detection element. 
According to a still further aspect of the present invention, a temperature 
detecting method by a semiconductor device provided with a temperature 
detecting diode constructed in such a manner as described above is 
characterized in that a pair of temperature detecting diodes are formed 
such that thermal resistances between the object of temperature detection 
element and the temperature detecting diodes are different from each 
other, and a temperature of the object of temperature detection element is 
calculated based on forward voltages of the pair of temperature detecting 
diodes. 
In any of the temperature detecting methods described above, means for 
constructing the different thermal resistances may include at the least 
distances between the object of temperature detection element and the 
temperature detecting diodes, and the temperature of the element may be 
detected by linear approximation based on the distances from the element 
to the pair of temperature detecting diodes. 
Alternatively, means for constructing the different thermal resistances may 
include at the least distances between the object of temperature detection 
element and the temperature detecting diodes, and the temperature of the 
element may be detected by second order approximation based on the 
distances from the element to the pair of temperature detecting diodes, 
assuming that the differential coefficient of the temperature of the 
object element for temperature detection is zero. 
According to the present invention, since the thermal resistance between 
the object of temperature detection element serving as a heat generating 
source and the temperature detecting diode is reduced, even if a high 
power is instantaneously applied, the temperature difference which may 
arise between the element and the temperature detecting element is 
reduced. Further, even if a temperature difference is produced between the 
element and the temperature detecting diode, by detecting the temperature 
of the element by calculation making use of the outputs of the two 
temperature detecting diodes, the temperature difference can be calculated 
to correct the temperature of the element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention are described below with reference to 
the drawings. 
Embodiment 1 
The first embodiment of the present invention is described with reference 
to FIGS. 7(a), 7(b) and 8. 
FIG. 7(a) is a schematic view of a construction of a pellet of a 
temperature detecting method showing the embodiment of the present 
invention, FIG. 7(b) is a sectional view taken along line W-W' of FIG. 
7(a), and FIG. 8 is a schematic sectional view showing a structure of 
essential part of the pellet. 
Referring to FIGS. 7(a) and 7(b), object element 302 for temperature 
detection in the form of a bipolar transistor, a field effect transistor 
or a like element and temperature detecting diode D1 are formed in a 
neighboring relationship on single silicon substrate 301, and also 
overheat protecting circuit 303 is formed on silicon substrate 301. Those 
elements are connected by aluminum wiring lines so that they may 
cooperatively form a semiconductor device having an overheat protecting 
function. 
The present embodiment is characterized in that temperature detecting diode 
D1 is formed at a location on the same pellet surrounded by object of 
temperature detection element 302, which serves as a heat source, and in 
which element 302 is partially located in the region to be used for wiring 
between temperature detecting diode D1 and overheat protecting circuit 
303. 
A structure of the essential part of the present embodiment is shown in 
FIG. 8. The present embodiment employs an N-channel field effect 
transistor of the enhancement type, and temperature detecting diode D1 
formed from terminals A and K in a block separated from source terminal S 
side of object of temperature detection element 302 is connected to a 
control circuit such as overheat protecting circuit 303 by means of an 
aluminum wiring line on the surface of the pellet. 
It is to be noted that temperature detecting diode D1 may be formed 
otherwise in a block at a location surrounded by object of temperature 
detection element 302 and separated from element 302. 
In the present embodiment, since temperature detecting diode D1 is formed 
in the block of element 302, the two elements are formed very closely to 
each other. 
Further, while element 302 and temperature detecting diode D1 
conventionally contact with each other over less than about one half their 
circumference, element 302 and temperature detecting diode D1 in the 
present embodiment contact with each other over substantially their full 
circumferences. Consequently, comparing with the prior art, the contacting 
portions between element 302 and temperature detecting diode D1 are 
increased to more than about two times in magnitude and the thermal 
resistance between them is reduced to less than about one half. Also the 
temperature difference which arises between element 302 and temperature 
detecting diode D1 is reduced to less than about one half. 
Embodiment 2 
The second embodiment of the present invention is described below with 
reference to FIGS. 9 and 10. 
FIG. 9 is a schematic sectional view showing a structure of the essential 
part of the second embodiment of the present invention. 
The present embodiment is different from the first embodiment described 
above in that insulator 401 of silicon dioxide or a like substance is 
formed on the surface of a pellet at a location which is surrounded by 
object of temperature detection element 302 and at which temperature 
detecting diode D1 is to be formed to establish insulation between element 
302 and temperature detecting diode D1, and in this condition, temperature 
detecting diode D1 is formed. 
The forming method of the present embodiment is advantageous in that, 
although an increased number of process steps are required, the degree of 
freedom of the position at which temperature detecting diode D1 is to be 
formed increases. 
FIG. 10 is a diagram showing a temperature distribution in a section of the 
semiconductor device including temperature detecting diode D1 (the section 
taken along line W-W' of FIG. 7) immediately after a high power is 
instantaneously applied to the semiconductor device of the construction 
described above. 
Where the applied power is represented by P, the maximum temperature of 
object element 302 for temperature detection is represented by Tmax, and 
the thermal resistance between temperature detecting diode D1 and element 
302 at position r is represented by Rth(r), temperature T(r) at position r 
of temperature detecting diode D1 in the present embodiment is given by 
following equation 2: 
EQU T(r)=Tmax-P.times.Rth(r) equation 2 
The temperature difference between the temperature of temperature detecting 
diode D1 and temperature Tmax of object element 302 for temperature 
detection in the present embodiment is P.times.Rth(r), and this 
temperature difference is smaller than temperature difference 
P.times.Rth(p) between temperature T(p) at position p of temperature 
detecting diode D1 of FIG. 6 which illustrates the temperature 
distribution of the conventional example and temperature Tmax of element 
302. Consequently, the thermal resistance can be reduced, and accordingly, 
the accuracy of the detected temperature can be improved. 
The present embodiment is advantageous in that, since temperature detecting 
diode D1 and element 302 have no overlapping portion between them, they 
can be produced by the same step as the conventional diffusion process. 
It is to be noted that it is otherwise possible to dispose element 302 
around the entire periphery of temperature detecting diode D1 and dispose 
a wiring line between temperature detecting diode D1 and overheat 
protecting circuit 303 on element 302. 
Embodiment 3 
Next, the third embodiment of the present invention is described with 
reference to FIGS. 11(a) and 11(b), 12 and 13. 
FIG. 11(a) is a schematic view showing a construction of a pellet according 
to the present embodiment, FIG. 11(b) is a sectional view taken along line 
X-X' of FIG. 11(a), and FIG. 12 is a schematic sectional view showing a 
structure of the essential part of the pellet. 
Referring to FIGS. 11(a) and 11(b), object of temperature detection element 
502 formed from a bipolar transistor, a field effect transistor or a like 
element and overheat protecting circuit 503 are formed on silicon 
substrate 501 by diffusion processing, and also temperature detecting 
diode D1 is formed on silicon substrate 501. 
The present embodiment is characterized in that heat conducting member 505 
of a metal material such as aluminum or copper is formed on the surface of 
the pellet over portions of temperature detecting diode D1 and object of 
temperature detection element 502 with insulating member 504 of silicon 
dioxide, alumina or a like substance interposed therebetween. Heat 
conducting member 505 is produced by forming, after formation of a pellet 
by a conventional method, a film of a metal material with the thickness of 
1 .mu.m, for example, on an insulating material of 0.2 .mu.m thick by 
sputtering or vapor deposition and then patterning only the metal film by 
ion etching or a like technique. 
FIG. 12 is a schematic sectional view showing a structure of the essential 
part of the present embodiment. The present embodiment is different from 
the conventional example shown in FIG. 4 in that heat conducting member 
505 of aluminum, copper or a like metal is formed on the surface of the 
pellet over both temperature detecting diode D1 and object element 502 for 
temperature detection while assuring insulation between them by means of 
insulating member 504 of silicon dioxide or a like material. 
Where copper is used for heat conducting member 505 provided over element 
502 and temperature detecting diode D1 in the present embodiment, since 
the thermal conductivity of it is higher by more than twice the thermal 
conductivity of silicon used as a substrate material and is higher than 
the thermal conductivity of a resin for encapsulation, the thermal 
resistance between element 502 and temperature detecting diode D1 can be 
reduced. 
FIG. 13 is a diagram illustrating a temperature distribution along a 
section of the semiconductor device of the construction described above 
including temperature detecting diode D1 (the section taken along line 
W-W' in FIG. 7) immediately after a high power is instantaneously applied. 
The curve indicated by an alternate long and short dash line in FIG. 13 is 
a re-representation of the temperature distribution of the conventional 
example illustrated in FIG. 6 when heat conducting member 505 is not 
involved. Meanwhile, the other curve indicated by a solid line presents 
the temperature distribution in the present embodiment. 
Where the applied power is represented by P, the maximum temperature 
element 502 is represented by Tmax, and the thermal resistance between 
temperature detecting diode D1 and element 502 at position p in the 
present embodiment is represented by Rth(p'), temperature T(p') at 
position p of temperature detecting diode D1 in the present embodiment is 
given by following equation 3: 
EQU T(p')=Tmax-P.times.Rth(p') equation 3 
The temperature difference between the temperature of temperature detecting 
diode D1 and temperature Tmax of element 502 in the present embodiment is 
P.times.Rth(p'), and this temperature difference is smaller than 
temperature difference P*Rth(p) between temperature T(p) at position p of 
temperature detecting diode D1 of FIG. 6 which illustrates the temperature 
distribution of the conventional example and temperature Tmax of object 
element 302. Consequently, the thermal resistance can be reduced, and 
accordingly, the accuracy of the detected temperature can be improved. 
It is to be noted that heat conducting member 505 between temperature 
detecting diode D1 and element 502 can otherwise be formed intermittently. 
Further, also it is possible to form heat conducting member 505 
simultaneously with the wiring step between the elements after the 
diffusion processing. 
Embodiment 4 
Next, the fourth embodiment of the present invention is described with 
reference to FIGS. 14(a) and 14(b), 15, 16 and 17. 
FIG. 14(a) is a schematic view showing a construction of a pellet according 
to the present embodiment, and FIG. 14(b) is a sectional view taken along 
line Y-Y' of FIG. 14(a). 
Referring to FIGS. 14(a) and 14(b), object element 602 for temperature 
detection and overheat protecting circuit 603 are formed on silicon 
substrate 601, and also temperature detecting diodes D1 and D2 are formed 
on silicon substrate 601. 
The present embodiment is characterized in that temperature detecting 
diodes D1 and D2 having the same specifications of FIGS. 14(a) and 14(b) 
are disposed at positions p and q with reference to position o and that 
temperature detecting circuit 604 forming overheat protecting circuit 603 
detects the temperature of element 602 by calculation making use of the 
outputs of two temperature detecting diodes D1 and D2. 
In particular, where the temperatures at positions p and q with reference 
to position o are represented by T(p) and T(q), temperature T(o) at 
reference position o of object element 602 for temperature detection is 
given by following equation 4: 
##EQU1## 
Here, reference position o is set in advance to a position in the proximity 
of object element 602 for temperature detection. 
An example wherein the calculation given by equation 4 above is performed 
by the hardware of temperature detecting circuit 604 is shown in FIG. 17. 
Detection current of several mA flows in a forward direction through two 
temperature detecting diodes D1 and D2. 
The voltage across temperature detecting diode D1 is VF(p) and is converted 
to voltage V4=q.times.VF(p) by resistors R1 and R2. The voltage across the 
other temperature detecting diode D2 is VF(q) and is converted into 
voltage V5=p.times.VF(q) by resistors R3 and R4. 
A difference between voltages V4 and V5 is detected by a differential 
circuit formed from transistors Tr3 and Tr4, and simultaneously, a voltage 
obtained by multiplying the difference by 1/(q-p) by means of resistors R5 
and R6 is outputted as voltage V6. Voltage V6 thus obtained is compared 
with reference voltage Vref set in advance by resistors R7 and R8 by 
comparator Cmp1 to detect whether or not voltage V6 is higher than 
reference voltage Vref, and a result of the comparison is outputted as 
voltage Vo from comparator Cmp1. Also the calculating circuit can be 
realized with a comparatively simple circuit construction in this manner. 
FIG. 15 is a diagram illustrating the temperature distribution on the 
section taken along line Y-Y' of FIG. 14 immediately after a high power is 
instantaneously applied to the semiconductor device of the present 
embodiment. 
Referring to FIG. 15, the actually measured values are temperatures T(p) 
and T(q) at positions p and q, and temperature To at the reference 
position is a calculated value. 
In the present embodiment, since temperature correction is performed by 
calculation, the temperature difference between temperature To of object 
of temperature detection element 602 thus obtained and actual temperature 
Tmax of element 602 is smaller than the temperature difference between 
temperature T(p) at position p of temperature detecting diode D1 of FIG. 6 
which illustrates the temperature distribution of the conventional example 
and temperature Tmax of element 102. Consequently, the accuracy of the 
detected temperature is improved. 
It is to be noted that, as another calculation method, the temperature of 
element 602 may be calculated by second order approximate calculation from 
the forward voltages of temperature detecting diodes D1 and D2 located at 
positions p and q with reference to position o assuming that the 
differential coefficient of the temperature at reference position o of 
element 602 is zero and that the positions and the forward voltages are in 
a relationship of a curve of the second order. 
In particular, where the temperatures at positions p and q with reference 
to position o of element 602 are represented by T(p) and T(q), temperature 
To of element 602 is calculated from following equation 5: 
##EQU2## 
FIG. 16 is a diagram illustrating the temperature distribution on the 
section taken along line Y-Y' of FIG. 14 immediately after a high power is 
instantaneously applied to the semiconductor device described above. The 
accuracy of the detected temperature is improved by an action similar to 
that in the case of the linear approximation described hereinabove with 
reference to FIG. 15. 
Further, since the upper expression and the lower expression of equation 5 
are different only in coefficients and can be represented in the same 
form, an actual circuit construction can be applied merely by changing the 
circuit constants of the temperature detecting circuit of linear 
approximation illustrated in FIG. 17 such that p is changed to p squared 
and q is changed to q squared. 
As described above, according to the present invention, by making use of 
the forward voltage of a temperature detecting diode, a temperature 
variation when a high power is instantaneously applied to an object 
element for temperature detection can be detected with a high degree of 
accuracy, and a semiconductor device having a temperature detecting 
function can be realized readily. Further, there is another advantage in 
that, when a high power is applied inadvertently, the possibility that the 
life of the semiconductor device may be reduced can be reduced. 
Furthermore, since the element temperature can be controlled with a high 
degree of accuracy so that it may not rise extraordinarily even upon 
short-circuiting of a load or in a like case, there is another advantage 
in that a device having a high resistance to destruction can be produced 
in a reduced size at a reduced cost.