JP2013084666A - Semiconductor element junction temperature estimation method, estimation system and estimation program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor element junction temperature estimation method, estimation system and estimation program which help to find the junction temperature of a semiconductor element with high accuracy.SOLUTION: A junction temperature estimation system 2 comprises: an arithmetic processing device 10; an input device 20; a storage device 30; and an output device 40. The storage device 30 stores energization condition and other information 32, voltage temperature characteristic information 34, and an arithmetic operation program 36. The arithmetic operation program 36 is a program stipulating an arithmetic process in which the junction temperature of a semiconductor element under a prescribed energization condition corresponding to an elapse of time after energization has started under the energization condition is calculated a prescribed number of times. When the arithmetic operation program 36 is executed, calculations are performed in steps, including the acquisition or calculation of T, the acquisition of a forward voltage Vat T, the acquisition of a Ivalue, the calculation of P, and the calculation of ΔT.

Description

  The present invention relates to a method for estimating a junction temperature of a semiconductor element, an estimation system, and an estimation program.

  Conventionally, for example, as disclosed in JP-A-4-340757, a system for detecting a junction temperature (junction temperature) of a semiconductor element is known. The junction temperature is the temperature of the semiconductor junction within the semiconductor element. If the semiconductor element is not used so that the junction temperature is within an appropriate range, the semiconductor element will be damaged. On the other hand, paragraph 0003 of this publication describes that the forward voltage of the diode is temperature-dependent, specifically, that the voltage between the two electrodes of the diode varies depending on the junction temperature of the diode. Yes. This publication discloses a system that detects the junction temperature of a semiconductor integrated circuit (LSI) using the temperature dependence of the forward voltage of a diode.

JP-A-4-340757 JP-A-9-304471 JP 2006-50711 A JP 59-167024 A

  However, the technique described in the above publication still has room for improvement in terms of calculation accuracy. That is, the technique according to the above publication relates to a temperature estimation method at the time of device measurement. Specifically, the technique estimates temperature by measuring a characteristic value of a semiconductor device. The characteristic value to be measured is, for example, a voltage value when a minute current is flowing.

  In the temperature estimation method in this prior art, the following points are not taken into consideration. That is, when the semiconductor element self-heats due to energization of the semiconductor element, the electrical characteristics of the semiconductor element change due to the self-heating. Originally, it is preferable to consider the temperature rise due to such self-heating during energization in the current calculation step and feed back the temperature change to the temperature rise calculation in the next calculation step. For example, the forward voltage may have a proportional temperature dependency in which the forward voltage increases in accordance with the increase in junction temperature due to self-heating. In other words, the temperature characteristic of the loss (product of the energization current and the forward voltage) in the semiconductor element may have a positive coefficient. In this case, if the temperature change due to self-heating is not taken into account (for example, if the forward voltage is a fixed value regardless of the temperature), an error that the estimated temperature is estimated to be lower than the actual junction temperature may occur. The conventional technology still has room for improvement in that the countermeasures against such errors have not been sufficiently studied.

  The present invention has been made to solve the above-described problems, and provides a semiconductor element junction temperature estimation method, estimation system, and estimation program capable of accurately obtaining a semiconductor element junction temperature. Objective.

In order to achieve the above object, according to a first aspect of the present invention, for a semiconductor element under a predetermined energization condition, a junction temperature of the semiconductor element that calculates a predetermined number of times of the junction temperature after the start of energization under the energization condition is calculated. An estimation system,
Means for obtaining a first junction temperature, which is a junction temperature at a first point in time in the semiconductor element;
Means for determining a forward voltage of the semiconductor element according to the first junction temperature according to a voltage temperature characteristic defining a relationship between a junction temperature and a forward voltage in the semiconductor element;
Obtaining a change based on the forward voltage according to the first junction temperature, an energization current of the semiconductor element, and a thermal resistance characteristic of the semiconductor element, and adding the change to the first junction temperature. Means for obtaining a second junction temperature that is a junction temperature of the semiconductor element at a second time point after the first time point on the time course;
It is characterized by providing.

According to a second aspect of the present invention, in order to achieve the above object, an arithmetic processing unit performs a process of calculating a predetermined number of times for a semiconductor element under a predetermined energization condition according to a lapse of time after the start of energization under the energization condition. A semiconductor device junction temperature estimation program to be executed by
A process of causing the arithmetic processing unit to acquire a first junction temperature, which is a junction temperature at a first time point in the time course, in the semiconductor element;
In accordance with a voltage temperature characteristic that defines a relationship between a junction temperature and a forward voltage in the semiconductor element, a process for causing the arithmetic processing device to acquire a forward voltage of the semiconductor element according to the first junction temperature;
Obtaining a change based on the forward voltage according to the first junction temperature, an energization current of the semiconductor element, and a thermal resistance characteristic of the semiconductor element, and adding the change to the first junction temperature. A process for causing the arithmetic processing unit to execute a calculation for obtaining a second junction temperature that is a junction temperature of the semiconductor element at a second time point after the first time point on the time passage;
It is characterized by providing.

According to a third aspect of the present invention, in order to achieve the above object, the junction temperature of a semiconductor element for calculating a junction temperature corresponding to the passage of time after the start of energization under the energization condition for a semiconductor element under a predetermined energization condition a predetermined number of times. An estimation method,
Obtaining a first junction temperature, which is a junction temperature at a first point in time in the semiconductor element,
Obtaining a forward voltage of the semiconductor element according to the first junction temperature according to a voltage temperature characteristic defining a relationship between a junction temperature and a forward voltage in the semiconductor element;
Obtaining a change based on the forward voltage according to the first junction temperature, an energization current of the semiconductor element, and a thermal resistance characteristic of the semiconductor element, and adding the change to the first junction temperature. Obtaining a second junction temperature that is a junction temperature of the semiconductor element at a second time point after the first time point over the time course;
It is characterized by providing.

  According to the present invention, the junction temperature of a semiconductor element can be obtained with high accuracy.

It is a flowchart for demonstrating the calculation procedure of the estimation method of the junction temperature of the semiconductor element concerning embodiment of this invention. It is a figure which shows the electricity supply condition to a semiconductor element in the estimation method of junction temperature in embodiment of this invention. It is a figure which shows an example of the measurement result of the relationship between junction temperature and forward voltage which should be acquired beforehand in the estimation method of the junction temperature of the semiconductor element concerning embodiment of this invention. It is a figure for demonstrating the estimation result obtained by the junction temperature estimation method of the semiconductor element concerning embodiment of this invention. It is a figure for demonstrating the estimation result obtained by the junction temperature estimation method of the semiconductor element concerning embodiment of this invention. It is a figure for demonstrating the 1st modification of the junction temperature estimation method of the semiconductor element concerning embodiment of this invention. It is a figure for demonstrating the failure probability calculation method using the junction temperature estimation method of the semiconductor element concerning embodiment of this invention. It is a figure for demonstrating the failure probability calculation method using the junction temperature estimation method of the semiconductor element concerning embodiment of this invention. It is a schematic diagram for demonstrating the junction temperature estimation system 2 of the semiconductor element concerning embodiment of this invention.

Embodiment.
[Method for Estimating Junction Temperature of Semiconductor Device According to Embodiment]
FIG. 1 is a flowchart for explaining a calculation procedure of a method for estimating a junction temperature of a semiconductor element according to an embodiment of the present invention. The arithmetic processing of the following steps can be provided as a computer-readable program or the like as will be described later.
The junction temperature estimation method according to the present embodiment can be applied to various semiconductor elements such as diodes and transistors. There are no limitations on the types and applications of the semiconductor elements, such as semiconductor elements used in electrical equipment such as various diodes incorporated in electronic circuits, various semiconductor chips, LSI chips, power control diodes, IGBTs and other power semiconductor elements. May be.

  As shown in FIG. 1, in the present embodiment, calculations of a plurality of steps S1, S2 to Sn are sequentially performed as shown in step S1, step S2,... Step Sn. The steps are not necessarily spaced at regular intervals, and each step may be assigned at an arbitrary interval. However, an equal interval has the advantage that the calculation is simple. Further, the step resolution (number of steps) should be as large as possible from the viewpoint of improving calculation accuracy.

In the flowchart of FIG. 1, the meaning of each symbol is as follows. The subscript “n” of each symbol represents a step number, and a number corresponding to a predetermined step is substituted such as n = 1, 2,.
T _jn means the junction temperature. This is the junction temperature (junction temperature) of the semiconductor element.
V _Fn means a voltage, and is a forward voltage generated during energization in the semiconductor element.
_IFn means current and is an energization current that flows during energization of the semiconductor element.
Z _{th (j−c) n} means a transient thermal resistance. Specifically, in this embodiment, it is a junction temperature and a transient thermal resistance between cases. The value of the transient thermal resistance is generally disclosed to the public, for example, by being described in a specification sheet (data sheet) for a semiconductor device product. Hereinafter, for simplification, it may be simply referred to as “Z _th ”.
ΔT _jn means a junction temperature difference. Specifically, in this embodiment, a junction temperature and a temperature difference between cases are used. The method for estimating the junction temperature according to the present embodiment takes into account the temperature rise due to self-heating of the semiconductor element during energization in a certain calculation step, and feeds back the temperature change to the temperature rise calculation in the next calculation step. Thus, this ΔT _jn can be included in the junction temperature calculation.

  FIG. 2 is a diagram showing energization conditions of the semiconductor element in the method for estimating the junction temperature in the embodiment of the present invention. Specifically, FIG. 2 is a time chart of energization current, transient thermal resistance, and forward voltage. As shown in FIG. 2, in this embodiment, the energization condition for applying a single pulse sine half wave to a semiconductor element is used. However, the present invention is not limited to this, and the calculation procedure (contents of the flowchart) according to the present embodiment is the same even when various other energized waveforms such as a plurality of pulses, a square wave, and a triangular wave are given to the semiconductor element. Can be used. The energization conditions are selected in advance before the execution of the flowchart of FIG. Also, the number of step divisions for calculation is determined in advance together with the setting of the energization conditions. In other words, in the present embodiment, the number of calculations to be performed within one cycle of the energization condition (half pulse sine half wave) shown in FIG. 2 is set in advance, and the time on the horizontal axis in FIG. , It is determined at what timing and at what step the calculation is executed.

FIG. 3 is a diagram illustrating an example of a measurement result of the relationship between the junction temperature and the forward voltage that should be acquired in advance in the method for estimating the junction temperature of the semiconductor element according to the embodiment of the present invention. The semiconductor device of estimation target according to the present embodiment, there is a proportional relationship between the junction voltage T _j and the forward voltage V _F as in FIG. 3, and as the junction voltage T _j increases forward voltage V _F is assumed to have the characteristics to deteriorate. However, the present invention is not limited thereto and may be a semiconductor device having a forward voltage V _F is also increased properties as e.g. junction voltage T _j increases. Further, the relationship between the two is not limited to a linear (proportional) correlation, and a semiconductor element having a curved forward voltage-junction temperature characteristic may be used.

Note that the characteristics shown in FIG. 3 are acquired in advance before executing the flowchart of FIG. For example, the relationship between the forward voltage and the junction temperature is measured in a constant energized current state while placing the semiconductor element (diode or transistor) in an environment where the temperature can be controlled by a thermostat or the like. Note that the relationship between the set temperature in the thermostatic chamber and the actual bonding temperature may be specified in advance by measurement, and generally the case temperature and surroundings on the data sheet published for semiconductor element products. You may calculate using the relational expression of temperature and joining temperature. The characteristics shown in FIG. 3 are recorded on the storage medium as readable information in the form of mathematical formulas (approximation formulas) or maps. In the case of linear approximation, a mathematical formula of V = a × T _j + b is recorded as in the linear graph of FIG. 3 (a and b are constants, respectively).

・・・（３）
これらの数式（１）〜（３）は、図１のフローチャートを実行する際に利用されるものである。
なお、本実施の形態にかかる推定方法を、推定プログラムや推定システムとして提供する場合には、コンピュータその他の演算処理装置がこれらの数式に従って演算を実行可能な状態において図１のフローチャートがスタートする。具体的には、コンピュータ等の記録媒体に上記数式が保存される。 As shown in each step S1, S2,... Sn in FIG. 1, the equation used to calculate the junction temperature T _jn is as follows.

... (3)
These mathematical formulas (1) to (3) are used when the flowchart of FIG. 1 is executed.
When the estimation method according to the present embodiment is provided as an estimation program or an estimation system, the flowchart of FIG. 1 starts in a state where a computer or other arithmetic processing device can execute an arithmetic operation according to these mathematical expressions. Specifically, the above mathematical formula is stored in a recording medium such as a computer.

In the flowchart of FIG. 1, first, a step of obtaining a value of n = 1 in T _jn , that is, T _j1 is performed (step S1). T _j1 coincides with T _{j_start in} Expression (1) in step S1, which is the first step. T _{j_start} is a predetermined initial value of T _j .
Next, the value of n = 1 in V _Fn , that is, V _F1 is acquired as the forward voltage at the temperature of T _j1 . V _F1 can be calculated by substituting (inputting) T _j1 for the approximate expression V _F = a × T _j + b of the characteristic of the straight line graph shown in FIG.
Then, find the value of _{I 1.} The value of I ₁ is from a predetermined pulse waveform as current conditions shown in FIG. 2, determined by reading the current value at the timing of step S1. P ₁ is calculated by multiplying V _F1 and I ₁ according to Equation (3). ΔT _j1 is calculated by further multiplying P ₁ by the transient thermal resistance Z _th . Here, in the present embodiment, the transient thermal resistance to be multiplied in each step is determined as follows. As in the first term on the right side of Equation (2), the final value Z _{th (j−c) n} and the value Z _{th (j−c) n immediately} before the final value in the time width for performing temperature estimation. Multiply the difference from ₋₁ by P _{1 of the} first step. In step S2, a calculation of P2 × ( _{Zth (j−c) n−1−} Zth _{(j−c) n−2} ) is performed, and this is similarly applied to the subsequent steps. That is, in the present embodiment, Z _thn multiplied by P ₁ is not Z _th1 .

As a result of these calculations, in step S1, first, the junction temperature T _j1 in step S1 is specified, and further, ΔT _j1 to be used in the next step S2 is calculated. Thereby, step S1 is completed.

Next, the process proceeds to step S2. In step S2, the sum of T _j1 and ΔT _j1 obtained in step S1 is calculated as the value of T _j2 . Thereby, the value of the junction temperature _Tj2 in step S2 is obtained.
_Thereafter, the forward voltage at a temperature of _{T j2,} n = 2 values in _{V Fn,} i.e. obtains the _{V F2.} V _{F2 is} also calculated by substituting (inputting) T _j2 for the approximate expression V = a × T _j + b of the characteristic of the straight line graph shown in FIG. 3 in the same manner as calculating V _F1 in step S1. can do.
Then, find the value of _{I 2.} The value of I ₂ is also determined by reading the current value at the timing of step S2 from the pulse waveform predetermined as the energization condition shown in FIG. 2 in the same manner as when I ₁ was obtained in step S1. Further, P ₂ is calculated by multiplying V _F2 and I ₂ according to Equation (3). Further multiplying the transient thermal resistance _{Z th} against P _2. The value of the transient thermal resistance _{Z th} to multiplied to P ₂ is a further value back by one step in time than _{Z th} when the step _{S1 (Z th (j-c} ) n-1 -Z th ( _{j-c) n-2} ). ΔTj2 is calculated by the following equation (4).

As a result of these calculations, in step S2, first, the junction temperature T _j2 in step S2 is specified, and further, ΔT _j2 to be used in the next step is calculated. Thereby, step S2 is completed.

Thus, in a certain step, the junction temperature T _jn in that step is specified, and ΔT _jn to be used in the next step is also calculated. By repeating this, calculation can be advanced from step S1 to the last step (step Sn). As a result, T _jn that is the junction temperature in the final step can be calculated.

FIG. 4 is a diagram for explaining an estimation result obtained by the method for estimating the junction temperature of a semiconductor element according to the embodiment of the present invention. FIG. 4 is a diagram showing a calculation result obtained by executing the above-described calculation procedure. In FIG. 4, it can be seen that T _j first increases and then changes to decrease. Thus, according to the present embodiment, the junction temperature of the semiconductor element can be accurately estimated by taking into account the change in forward voltage due to self-heating. As described above, according to the present invention, it is possible to accurately estimate the junction temperature from the loss (product of forward current _IFn and forward voltage _VFn ) applied to the semiconductor element and the transient thermal resistance value _Zth. .

FIG. 5 is a diagram for explaining an estimation result obtained by the method for estimating the junction temperature of a semiconductor element according to the embodiment of the present invention. Figure 5 is a diagram showing a result of forward voltage upon adding the temperature dependence of was calculated for the relationship between the forward voltage V _Fn energized current I _Fn when energized. Characteristic indicated by the straight line in FIG. 5, are those described energization current I _Fn relationship between the forward voltage V _Fn in the case where the temperature conditions fixed. In FIG. 5, a plurality of plotted points describe the relationship between the forward voltage V _Fn and the conduction current I _Fn calculated by the calculation method according to the above embodiment. The plurality of plotted points are V _F1 , V _F2 ,... _VFn obtained in the calculation process up to steps S1, S2 _,.
Note that this embodiment exemplifies a case where the semiconductor element has a tendency that _VFn decreases due to self-heating of the semiconductor element by energization. That is, it is a semiconductor element having a negative temperature coefficient.

(Modification)
FIG. 6 is a diagram for explaining a first modification of the semiconductor element junction temperature estimation method according to the embodiment of the present invention. In the following modification, the leakage current characteristic is included in the calculation of the junction temperature estimation method according to the above embodiment while considering that the leakage current characteristic has temperature dependence.

  FIG. 6 is a diagram showing the relationship between the leakage current and the junction temperature Tj under a constant applied voltage condition. As an application of a power semiconductor element, it is common to apply a voltage to the semiconductor element after completion of energization. When a voltage is applied to the semiconductor element, a leakage current (reverse current in the case of a diode) flows, and the product of the leakage current and the applied voltage becomes a loss. The leakage current has a positive coefficient in relation to the junction temperature. In particular, in high temperature conditions, the leakage current often increases exponentially.

In this modified example, when a voltage is applied after completion of energization (applied voltage value V _ap ), the leakage current at the junction temperature at that voltage condition is obtained. _{Let the} leakage current be I _leakage, and in this modification, the magnitude of the leakage current is obtained by the following approximate expression. a _lk and b _lk are constants.
I _leakage = a _lk × exp (b _lk × T _jn ) (5)
The applied voltage value V _ap is integrated with the leakage current value I _leakage calculated by the equation (5). This product value P ′ is added to the loss calculation formula for each step (that is, P _n = I _Fn × V _{Fn in} formula (3)). Thereby, the estimation accuracy of junction temperature at the time of voltage application after completion of energization is improved.
Note that a relational expression between the leakage current and the applied voltage is obtained in advance for a plurality of applied voltages (V _ap1 , V _ap2 ,... V _apn ) _having different values, and the relational expression is selected according to the applied voltage value every time. May be used. Thereby, when there are a plurality of different applied voltage conditions, it is possible to calculate an appropriate leakage current using the characteristic (relational expression) according to the current applied voltage condition.

Hereinafter, a second modification of the semiconductor device junction temperature estimation method according to the embodiment of the present invention will be described. A transient voltage is generated by the current increase rate (di / dt) when the current is flowing. This transient voltage approximation formula may be added to the _VFn calculation formula. Specifically, the characteristics of the transient voltage V corresponding to the current increase rate (di / dt) are measured in advance, and an approximate expression of the characteristics is obtained. It is assumed that the transient voltage value calculated by the approximate expression of this characteristic is added to the second term _VFn on the right side of Expression (3) described above. This further improves the accuracy of estimation of the junction temperature.

(Application to failure probability calculation)
7 and 8 are diagrams for explaining a failure probability calculation method using the method for estimating the junction temperature of a semiconductor device according to the embodiment of the present invention. If the temperature at the time of breakdown of the semiconductor element (breakdown temperature) is grasped in advance by a limit test or the like due to overcurrent, the failure probability can be predicted by comparing the breakdown temperature with the junction temperature T _jn . The specific procedure is shown below. In the following description, the breakdown temperature is expressed as T _break .

(1) Performing a limit test First, a limit test is performed on a plurality of (generally, about 5 to 10) semiconductor element samples. For each semiconductor element sample, the energization current is gradually increased (increased loss) under certain energization conditions until breakdown.

(2) Fracture temperature analysis (for example, Weibull distribution analysis as shown in FIG. 8)
In the above limit test, the current value at the intermediate value or the current value immediately before or at the time of destruction can be plotted on a graph according to the Weibull distribution or extreme value probability distribution, and the current value corresponding to the failure probability can be calculated. Like that. According to the analysis in which the failure probability-current value is plotted, for example, the current value is 1200 A at the failure probability F (t) = 10%, the current value is 1000 A at the failure probability F (t) = 1%, and the like. In addition, the current value corresponding to the failure probability can be calculated.

(3) Junction temperature calculation An estimation method according to the embodiment (calculation according to the flowchart of FIG. 1) for the junction temperature T _jn according to the current conditions obtained by the above analysis (for example, 1200 A or 1000 A as described above). Calculated by Thus, T _jn calculated from the result of the “(1) limit test” and “(2) breakdown temperature analysis” is a certain failure probability (for example, F (t) = 10% or 1% as described above). It represents the failure temperature at. This failure temperature is a use limit temperature of the semiconductor element, and is a breakdown temperature T _break at which the semiconductor element loses its function. In addition, you may obtain | require previously the relationship (approximation formula etc.) of _Tjn and failure probability F (t) like FIG. As a result, the failure probability under the energized condition to be examined can be easily calculated, and the failure can be easily predicted.

(4) Temperature comparison between T _break and T _jn Thereafter, the use limit temperature T _break is compared with the junction temperature T _jn under the energized condition to be examined. By this comparison, it is possible to predict the failure probability of the semiconductor element under the energized condition to be examined. For example, if T _break > T _{jn as} a result of the temperature comparison, it can be concluded that the junction temperature T _jn under the energization condition calculated this time does not reach the breakdown temperature T _break at a certain failure probability. On the other hand, when T _break ≦ T _jn , it can be concluded that the junction temperature T _jn under the energization condition calculated this time reaches the breakdown temperature with a certain failure probability.

Thus, by calculating the junction temperature T _jn for a desired energization condition and comparing it with the breakdown temperature T _break , the probability of failure and the failure probability under any energization condition can be calculated. _{Alternatively} , the T _j1 and I _Fn conditions at an arbitrary failure probability can be calculated by performing a reverse calculation from the failure probability. By performing these calculations, it is possible to accurately estimate the failure probability of the semiconductor element in a scene where the semiconductor element is desired to be used under a certain energization condition.

[Semiconductor device junction temperature estimation system and estimation program]
FIG. 9 is a schematic diagram for explaining the semiconductor element junction temperature estimation system 2 according to the embodiment of the present invention. In other words, the junction temperature estimation system 2 can be constructed by installing the junction temperature estimation program according to the embodiment of the present invention on the computer hardware described below. The junction temperature estimation system 2 executes a junction temperature estimation program on the arithmetic processing unit (computer) 10. According to the flowchart of FIG. 1, the junction temperature estimation program sets the junction temperature corresponding to the elapsed time after the start of energization under the energization condition for a predetermined number of times for a semiconductor element (specifically, a diode or a transistor) under the predetermined energization condition. It is a simulation program that can be repeatedly calculated only. The junction temperature estimation program may be provided (produced, transferred, etc.) as a state recorded on various computer-readable recording media (that is, a computer-readable recording medium recording the junction temperature estimation program). good.

  The junction temperature estimation system 2 includes an arithmetic processing device (computer) 10 and peripheral devices (an input device 20, a storage device 30, and an output device 40). The input device 20 is a human interface device such as a keyboard or a mouse, or a reading device for reading electronic information from a computer readable recording medium (CD-ROM, DVD-ROM or other various optical or magnetic recording devices). CD drive, DVD drive, etc.). An input / output interface for connection with a USB memory device or the like can also function as the input device 20. The output device 40 includes various output devices such as a monitor and a printer. The output device 40 displays and outputs the junction temperature estimation result (see FIG. 4) and the failure probability (%) according to the above-described embodiment.

  In the junction temperature estimation system 2, information 32 such as energization conditions, voltage temperature characteristics 34, and a calculation program 36 are stored in the storage device 30.

The energization condition information 32 is information defining energization conditions and the like as described with reference to FIG. The energization condition information 32 is information for specifying an energization condition in which the semiconductor element to be estimated is to be placed. In the present embodiment, the energization condition for applying the single pulse sine half wave of FIG. That is, the energization condition information 32 includes information in which the energization current waveform and the forward voltage waveform of the single pulse sine half wave shown in FIG. 2 are both expressed as a function of time. Further, the energization condition information 32 includes the value of the transient thermal resistance Zth as a function of time. Note that T _{j_start} which is an initial value of T _jn may also be included in the energization condition information 32.

The voltage temperature characteristic 34 is a characteristic that defines the relationship between the junction temperature and the forward voltage in the semiconductor element. The voltage temperature characteristic 34 stores the characteristic described with reference to FIG. 3, and the forward voltage value corresponding to the junction temperature can be obtained according to the voltage temperature characteristic 34. As described in the explanation of FIG. 3, a mathematical expression V = a × T _j + b may be recorded as the voltage-temperature characteristic 34 in the case of linear approximation.

The calculation program 36 is obtained by providing calculation processing for each step included in the flowchart of FIG. 1 as a program for an electronic computer. The arithmetic program 36 includes a subroutine including the functions of the mathematical formulas (1) to (3) and a main routine of program start → step S 1 → S 2 →... → Sn → program end.
The step of obtaining the junction temperature estimation value is also specified at the stage before the junction temperature estimation program is executed. The step interval (in other words, the step interval) specifies how many calculations are performed during the energization period (one cycle of a single pulse sine half wave in FIG. 2) specified by the energization condition information 32. It is a numerical value (parameter) and can be set (input) by the user of the junction temperature estimation system 2 via the input device 20.

In such a junction temperature estimation system 2, a calculation process is performed according to the flowchart of FIG. In the flowchart of FIG. 1, the meaning of each symbol is as follows. The subscript “n” of each symbol represents a step number, and a number corresponding to a predetermined step is substituted such as n = 1, 2,. The arithmetic processing unit 10 stores the values of the forward voltage V _Fn , the energizing current I _Fn , and the transient thermal resistance Z _{th (j−c) n at} the current step (S1, S2,... Sn) in the storage device 30. It is obtained by referring to the energization condition etc. information 32 inside. The arithmetic processing unit 10 executes the arithmetic program 36 while acquiring the forward voltage V _{Fn and the} like necessary for the calculation in each step of the flowchart of FIG. 1 from the energization condition information 32 and the voltage temperature characteristic 34. . That is, by executing the arithmetic program 36, in steps, the acquisition or calculation of T _jn as described above, the acquisition of the forward voltage V _Fn at T _jn , the acquisition of the value of I ₁ , the calculation of P _n , and ΔT _jn Calculation is performed.

Thus, in a certain step of the calculation program 36, the junction temperature T _jn in that step is specified, and ΔT _jn to be used in the next step is also calculated. By repeating such arithmetic processing up to the predetermined number of steps in the arithmetic processing unit 10, the calculation can be advanced from step S1 to the last step (step Sn). As a result, T _jn that is the junction temperature in the final step can be calculated. Thereafter, the calculation results T _j1 , T _j2 ,... T _jn can be displayed on the output device 40 as numerical data or as a graph as shown in FIG.

  Note that the first modification, the second modification, and application to failure probability estimation in the above-described embodiment may also be executed on the junction temperature estimation system 2 and the junction temperature estimation program.

For the first modification, for example, the following function (subroutine) may be added to the arithmetic program 36 and executed.
_-Function of Equation (5) for calculating leakage current I _leakage- Function for calculating product of leakage current value and applied voltage value-This product value is calculated as a loss calculation formula for each step (P _{n in} Equation (3)) = I _Fn × V _Fn ) A relational expression for leakage current and applied voltage may be obtained in advance, and this relational expression may be stored in the storage device 30. When there are a plurality of different applied voltage conditions, the leakage current may be calculated using a characteristic (relational expression) according to the current applied voltage condition.

For the second modification, for example, the following function (subroutine) may be added to the arithmetic program 36 and executed.
A function of an approximate expression of a transient voltage (transient voltage) generated by a current increase rate (di / dt) A routine for adding the calculated transient voltage value to the second term _VFn on the right side of Expression (3)

For application to failure probability calculation, for example, the following function (subroutine) may be added to the arithmetic program 36 and executed.
Data based on the analysis result obtained by performing the limit test (that is, a function for calculating a current value corresponding to the failure probability) and the junction temperature T _jn corresponding to the analyzed current condition are calculated by the calculation program 36 ( A routine for calculating with a calculation according to the flowchart of FIG. 1 (a function that defines the relationship between T _jn and failure probability (approximate expression etc.) as shown in FIG. 7). Note that a plurality of data based on the analysis result may be prepared such that D _10% , D _1% ,... For failure probability F (t) = 10%, 1%,.
A user interface for obtaining input information (energization condition and energization current for which failure probability is to be investigated) from the user. A routine for calculating the temperature of T _break and T _{jn. A} routine for outputting the comparison determination result to the output device 40.

2 Junction Temperature Estimating System 10 Arithmetic Processing Device 20 Input Device 30 Storage Device 32 Energization Condition Information 34 Voltage Temperature Characteristic 36 Operation Program 40 Output Device

Claims (7)

A semiconductor element junction temperature estimation system that calculates a predetermined number of times the junction temperature according to the passage of time after the start of energization under the energization condition for a semiconductor element under a predetermined energization condition,
Means for obtaining a first junction temperature, which is a junction temperature at a first point in time in the semiconductor element;
Means for determining a forward voltage of the semiconductor element according to the first junction temperature according to a voltage temperature characteristic defining a relationship between a junction temperature and a forward voltage in the semiconductor element;
Obtaining a change based on the forward voltage according to the first junction temperature, an energization current of the semiconductor element, and a thermal resistance characteristic of the semiconductor element, and adding the change to the first junction temperature. Means for obtaining a second junction temperature that is a junction temperature of the semiconductor element at a second time point after the first time point on the time course;
A junction temperature estimation system for a semiconductor device, comprising: The means for obtaining the second bonding temperature is:
Means for obtaining an integrated value of the forward voltage according to the first junction temperature and the energization current of the semiconductor element at the first time point;
In the case where the thermal resistance characteristic is divided into the predetermined number of times according to the passage of time, the value corresponding to the first time point when calculated backward from the final value of the thermal resistance characteristic divided into the predetermined number of times. Means for obtaining a difference between an order value one order before and an order value corresponding to the first time point;
Means for obtaining the change based on an integrated value of the integrated value and the difference;
Means for determining the second junction temperature by adding the change to the first junction temperature;
The semiconductor device junction temperature estimation system according to claim 1, comprising: According to the leakage current temperature characteristic that defines the relationship between the junction temperature and the leakage current value in the semiconductor element, according to the junction temperature when an applied voltage is applied to the semiconductor element after energization of the semiconductor element A means for obtaining a leakage current value;
3. The semiconductor element junction temperature estimation system according to claim 1, wherein a loss value determined based on a product of the leakage current value and the applied voltage is included in a calculation for obtaining the change. 4.   The transient voltage value calculated according to the transient characteristic that defines the relationship between the current increase rate during energization of the semiconductor element and the transient voltage generated during the energization is the order in the calculation for obtaining the change. 4. The junction temperature estimation system for a semiconductor device according to claim 1, wherein the system is included in a value of a directional voltage. Means for acquiring a failure probability characteristic that defines a relationship between an energization condition in which the semiconductor element is broken and a failure probability;
Means for estimating an estimated value of the junction temperature of the semiconductor element under energization conditions in which the semiconductor element is destroyed using the semiconductor element junction temperature estimation system according to any one of claims 1 to 4;
Means for estimating an estimated value of the junction temperature of the semiconductor element for energization conditions for which a failure probability is to be estimated using the semiconductor element junction temperature estimation system according to any one of claims 1 to 4;
Based on a comparison between an estimated value of the junction temperature of the semiconductor element under an energization condition in which the semiconductor element is destroyed and an estimated value of the junction temperature of the semiconductor element with respect to an energization condition for which a failure probability is to be estimated, Means for estimating the failure probability of the semiconductor element for energization conditions for which the probability is to be estimated;
A failure probability estimation system for a semiconductor device, comprising: A semiconductor element junction temperature estimation program for causing an arithmetic processing unit to execute a process for calculating a predetermined number of times a junction temperature according to the passage of time after starting energization under the energization condition for a semiconductor element under a predetermined energization condition,
A process of causing the arithmetic processing unit to acquire a first junction temperature, which is a junction temperature at a first time point in the time course, in the semiconductor element;
In accordance with a voltage temperature characteristic that defines a relationship between a junction temperature and a forward voltage in the semiconductor element, a process for causing the arithmetic processing device to acquire a forward voltage of the semiconductor element according to the first junction temperature;
Obtaining a change based on the forward voltage according to the first junction temperature, an energization current of the semiconductor element, and a thermal resistance characteristic of the semiconductor element, and adding the change to the first junction temperature. A process for causing the arithmetic processing unit to execute a calculation for obtaining a second junction temperature that is a junction temperature of the semiconductor element at a second time point after the first time point on the time passage;
A junction temperature estimation program for a semiconductor element, comprising: For a semiconductor element under a predetermined energization condition, a semiconductor element junction temperature estimation method for calculating a predetermined number of times the junction temperature according to the passage of time after the start of energization under the energization condition,
Obtaining a first junction temperature, which is a junction temperature at a first point in time in the semiconductor element,
Obtaining a forward voltage of the semiconductor element according to the first junction temperature according to a voltage temperature characteristic defining a relationship between a junction temperature and a forward voltage in the semiconductor element;
Obtaining a change based on the forward voltage according to the first junction temperature, an energization current of the semiconductor element, and a thermal resistance characteristic of the semiconductor element, and adding the change to the first junction temperature. Obtaining a second junction temperature that is a junction temperature of the semiconductor element at a second time point after the first time point over the time course;
A method for estimating a junction temperature of a semiconductor element, comprising:

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