JPH11274511A - Method and apparatus for analyzing circuit of semiconductor integrated circuit, computer readable storage medium storing circuit analysis program, and semiconductor integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to test a threshold voltage of an SOI(silicon on insulator)-MOSFET with a floating body node. SOLUTION: A circuit equation solving unit 4A outputs data relating to a threshold voltage of an SOI-MOSFET with a floating body node. The data from the circuit equation solving unit 4A is stored in a memory unit 6. The threshold voltage of the SOI-MOSFET with a floating body node is tested by a floating check unit 7 using the data stored in the memory unit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit analyzing method and a circuit analyzing apparatus used for designing a semiconductor integrated circuit, and more particularly to a circuit analyzing method used for designing a semiconductor integrated circuit including an SOI (silicon-on-insurator) -MOSFET. The present invention relates to a method and a circuit analysis device. The present invention also relates to a semiconductor integrated circuit designed using the circuit analysis method or the circuit analysis device.

[0002]

2. Description of the Related Art In general, as a method for checking the operation of a semiconductor integrated circuit using a computer, there is a circuit analysis method for formulating and analyzing the circuit operation. For example, a circuit simulation is included in such a circuit analysis method. SOI
-A circuit simulator (circuit analysis device) is an indispensable tool in order to increase the efficiency of the development of LSIs including MOSFETs.

[0003] SOI-MOSF in a semiconductor integrated circuit
There are two ways to use ET. One is SOI-MO
SOI-MO with SFET body floating
This is a method of effectively utilizing the design resources of a four-terminal bulk MOSFET, which has been widely used, by treating the SFET as a four-terminal element.
This is a method of fixing the body potential of the MOSFET. SO
To fix the body voltage of the I-MOSFET, SO
It is necessary to handle the I-MOSFET as a five-terminal element. When using a circuit simulator to analyze a semiconductor integrated circuit including an SOI-MOSFET, it is necessary to specify whether the body is floating or the body potential is fixed for each SOI-MOSFET. become. SOI-MOSFET caused by floating body
Specific behaviors include kink phenomena in the saturation region,
The frequency dependency of the delay time is typical.

Here, a conventional circuit analysis method and a conventional circuit analysis apparatus will be described with reference to FIGS. FIG.
FIG. 2 is a block diagram illustrating a configuration of a circuit analysis device. The circuit analysis device 1 reads an input file 2 in which circuit connection information is described. The circuit analysis device 1 analyzes the circuit operation based on the circuit connection information, obtains the voltage of each node in the circuit and the current of the voltage definition branch, and changes the voltage of a predetermined node of the circuit, the input / output current of the circuit, and the like. Output data about Therefore, the conventional circuit analyzer 1 includes a data file input processing unit 3, a circuit equation solving unit 4, and a waveform output unit 5. The data file input processing unit 3 reads the input file 2 and creates simultaneous nonlinear equations based on the circuit connection information. The circuit equation solving unit 4 obtains, from the circuit equation obtained by the data file input processing unit 3, a node voltage and a current of a voltage definition branch, which are solutions of the circuit equation. The waveform output unit 5 displays a voltage change of a predetermined node indicating a circuit operation or data of a current flowing through the predetermined node from the series of calculation results of the circuit equation solving unit 4 on a CRT, for example, by graphic display on the CRT. Report to operator.

Further, the operation of the conventional circuit equation solving section 4 will be described with reference to FIG. FIG. 5 shows an operation in a case where a change in each node voltage is graphically displayed with time taken on the horizontal axis. First, the circuit equation solving section 4 inputs a circuit equation from the data file input processing section 3 (step ST1). Next step ST2
Thus, the circuit equation solving section 4 discretizes the circuit equation.
For the discretization of the equation, for example, a numerical integration method such as a trapezoidal method is used. The discretized equation is obtained in step ST3.
And is solved by iterative calculation using a linearization method such as Newton's method. In step ST4, a change is obtained for each node voltage in the circuit every time.

When an SOI-MOSFET whose body node is floating exists in the circuit connection information, the circuit analysis device 1 performs a circuit analysis using, for example, an equivalent circuit model shown in FIG. . Gate node 1
Between 0 and the body node 14, there is a gate-body capacitance C _GfB determined by the gate oxide film thickness. Further, between the back gate node 13 and the body node 14, a back gate-body capacitance C depending on the buried oxide film thickness is provided.
_GbB exists. The diode 16 connected between the source node 11 and the body node 14
Recombination current component I _BS flowing through PN junction between sources
Is represented. The current flowing between the drain node 12 and the body node 14 includes a body-drain generated current I _BD represented by the diode 17 and a current component I _ii represented by the constant current source 18. The current component _Iii is a current relating to impact ions generated in the high electric field region at the drain end.

Body node 14 of SOI-MOSFET
Is floating, the body potential V _BS at each time point of the analysis is obtained from Kirchhoff's current law for the body node 14. The threshold voltage V _th of the SOI-MOSFET depends on the potential of the body node 14, and the time t and the body potential V _BS
Is obtained as a function of The circuit analysis device 1 performs a circuit analysis using a threshold voltage V _th that varies with time. That is, as shown in FIG. 7, the data 20- ₁ ~20- _n of the threshold voltage V _th at each time t ₁ ~t _n is generated. However, the threshold voltage V of the SOI-MOSFET
Information about _th is not output from the conventional circuit analysis device 1. For example, JP-A-1-94484 discloses that
A circuit simulator incorporating a model of a change in threshold voltage of a normal MOSFET is disclosed. However, this is a simulator for simulating long-term reliability deterioration characteristics, and calculates how the apparently stable threshold voltage of a MOSFET deteriorates in the long term. It does not monitor the threshold voltage of an SOI-MOSFET whose body node is floating, which changes every moment depending on the operation state of the circuit.

[0008]

SUMMARY OF THE INVENTION SOI-MOSFET
, The chip size of the semiconductor integrated circuit is prevented from increasing due to the body contact for fixing the body potential of the SOI-MOSFET, and the bulk M
In order to use OSFET effectively, SOI-
It is conceivable that the body of the MOSFET is floating. However, when the body node is floated, the body potential is not stable, so the SOI-MOSFE
The threshold voltage of T changes to make the operation of the semiconductor integrated circuit unstable, making it difficult to meet a predetermined standard and making design difficult. The conventional circuit analysis method and the conventional circuit analysis device are configured as described above, and do not output information about the threshold voltage of the SOI-MOSFET in the semiconductor integrated circuit, thereby facilitating circuit design. There is no problem. Further, in a conventional semiconductor integrated circuit, the SOI-M in which the fluctuation of the threshold voltage becomes larger than a predetermined value is used.
The problem that OSFETs and SOI-MOSFETs that do not have such a body contact are not provided, and the stability of circuit operation and the improvement of integration are not harmonized, one of which is sacrificed. There is.

The present invention is directed to all SOI-MOs having a body node floating in a semiconductor integrated circuit.
It is an object of the present invention to obtain a circuit analysis method and a circuit analysis device capable of automatically selecting SFETs that deviate from a predetermined standard with respect to fluctuations in threshold voltage and outputting information on the selected SOI-MOSFET. . It is another object of the present invention to provide a semiconductor integrated circuit in which the stability of the circuit operation and the improvement of the integration degree are harmonized by using such an analysis method or an analysis apparatus.

[0010]

According to a first aspect of the present invention, there is provided a circuit analysis method for a semiconductor integrated circuit comprising a plurality of SOI-MOSFEs.
A circuit analysis method for analyzing a circuit operation of a semiconductor integrated circuit including T, wherein a threshold value of the plurality of SOI-MOSFETs that changes every time during operation of the semiconductor integrated circuit because a body node is floating. Outputting data relating to a voltage; and determining, from the plurality of SOI-MOSFETs, an SO that does not conform to a predetermined standard relating to a threshold voltage based on the data relating to the threshold voltage.
Selecting an I-MOSFET.

According to a second aspect of the present invention, in the circuit analysis method for a semiconductor integrated circuit according to the first aspect, the step of selecting the plurality of SOI-MOSFETs includes the step of selecting the plurality of SOI-MOSFETs. SOI-MOSFET exceeding the predetermined reference value by comparing the variation with a predetermined reference value
And a step of selecting

According to a third aspect of the present invention, in the circuit analysis method for a semiconductor integrated circuit according to the second aspect, the step of selecting the plurality of SOI-MOSFETs includes the step of selecting the plurality of SOI-MOSFETs. SOI-MO exceeding the predetermined average value by comparing the average value of the fluctuation amount with the predetermined average value
Selecting an SFET.

A fourth aspect of the present invention is directed to a circuit analyzing apparatus, comprising: a plurality of SOI-Ms each having a floating body node;
A circuit analysis device for analyzing a circuit operation of a semiconductor integrated circuit including an OSFET, wherein the plurality of SOI-Ms in a circuit are analyzed.
A circuit equation solver for finding a change with time in the threshold voltage of the OSFET; a memory for storing data relating to the threshold voltages of the plurality of SOI-MOSFETs obtained by the circuit equation solver; The plurality of SOI-MOSFs based on data stored in the
A floating check unit for checking the threshold voltage of the ET.

A computer-readable recording medium storing a circuit analysis program according to a fifth aspect of the present invention is a computer-readable recording medium used when a computer analyzes a circuit operation of a semiconductor integrated circuit including a plurality of SOI-MOSFETs. Wherein the plurality of SOI-MOSFETs are changed based on threshold voltages of the plurality of SOI-MOSFETs that change during operation of the semiconductor integrated circuit because the body node is floating.
Wherein a circuit analysis program for causing a computer to execute a process of selecting an SOI-MOSFET that does not conform to a predetermined threshold voltage standard from among the above is stored.

A semiconductor integrated circuit according to a sixth invention is a semiconductor integrated circuit including a plurality of SOI-MOSFETs, wherein the plurality of SOI-MOSFETs are all SOI-MOSFETs.
-In the operation of the semiconductor integrated circuit when the body node of the MOSFET is floating, the first SOI-MO having a threshold voltage variation exceeding a predetermined reference value.
In the operation of the semiconductor integrated circuit when the body nodes of all the SOI-MOSFETs are floating, the semiconductor integrated circuit includes an SFET and a second SOI-MOSFET whose variation in threshold voltage does not exceed the predetermined reference value. The first SOI-MOSFET has a body contact, and the second SOI-MOSFET does not have a body contact.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing a configuration of a circuit analysis device according to an embodiment of the present invention. The circuit analysis apparatus 1A shown in FIG. 1 includes a data file input processing unit 3 and a waveform output unit 5 similar to those of the related art. The circuit analysis device 1A further includes a circuit equation solving unit 4A. The circuit equation solving section 4A of the conventional circuit analysis apparatus 1
Has new features. Further, the circuit analysis device 1A shown in FIG.
The storage unit 6 for storing data relating to the threshold value of the OI-MOSFET and the S in which the body node is floating
And a floating check unit 7 for checking the threshold voltage of the OI-MOSFET.

In the circuit analyzer 1A, the data file input processing unit 3, the circuit equation solving unit 4A, and the waveform output unit 5
Cooperates with each other to analyze the circuit operation based on the circuit connection information, obtain the voltage of each node in the circuit and the current of the voltage definition branch, and determine the change in voltage for a predetermined node of the circuit, the input / output current of the circuit, etc. The operation of outputting the data is the same as the operation performed by the data file input processing unit 3, the circuit equation solving unit 4, and the waveform output unit 5 of the circuit analysis device 1 in cooperation. The circuit analysis device 1A is different from the conventional circuit analysis device 1 in that the SO has a body node floating.
A change in the threshold voltage of the I-MOSFET can be monitored. As a result of the circuit simulation, the circuit analysis device 1A can detect and notify the fluctuation of the threshold voltage that does not satisfy the condition specified in advance, and thereby, the SOI in which the threshold voltage must be fixed.
-MOSFETs and SOI-MOSFETs that are not can be sorted out.

The circuit analyzer 1A is an SOI-MOSFE
In order to monitor the fluctuation of the threshold voltage of T, a new function is added to the circuit equation solving unit 4A and the storage unit 6
And a floating check unit 7. FIG. 2 is a flowchart for explaining the operations of the circuit equation solving unit 4A, the storage unit 6, and the floating check unit 7 when monitoring the fluctuation of the threshold voltage of the SOI-MOSFET. The circuit equation solving unit 4A
As in the conventional case, steps ST1 to S shown in FIG.
The circuit equation is solved by T4 to output data relating to each node voltage in the circuit. At this time, the circuit equation solving unit 4A outputs to the storage unit 6 data on the threshold voltage of the SOI-MOSFET (see FIG. 7) obtained during the calculation in steps ST3 and ST5. SOI-MOSFET threshold voltage V _th
The amount of variation is determined by the number 1, using the body potential V _BS at each time point of the analysis from the current law Kirchhoff's related body node.

[0019]

(Equation 1)

The floating check unit 7 processes the data relating to the threshold voltage stored in the storage unit 6 in steps ST6 and ST7, and monitors a change in the threshold voltage of the SOI-MOSFET. That is, the floating check unit 7 classifies the change in threshold voltage for each transistor (step ST6), and compares the range of change in the threshold voltage of each transistor with a reference value (step ST7). For example, the floating check unit 7 searches the entire circuit to be analyzed for SOI-MOSFETs in which the fluctuation amount of the threshold voltage _Vth increases due to the floating effect of the body, and highlights the SOI-MOSFET in the circuit diagram on the screen. Display (warning).

According to the circuit analyzer 1A, the reference to be compared by the floating check unit 7 can be set in any manner, and the operator can automatically specify the node whose fluctuation of the threshold voltage is to be analyzed without automatically specifying the node to be analyzed. It is possible to select SOI-MOSFETs in which the effect of the floating effect is large. Depending on the setting of the reference for the fluctuation of the threshold voltage of the SOI-MOSFET, the timing at which the effect becomes large, operating conditions, and positions in the circuit. Can be obtained comprehensively.

FIG. 3 is a graph showing an example of a change in threshold voltage of one SOI-MOSFET.
ΔV _th (t _n ) in FIG. 3 is the amount of change in the threshold voltage at time t _n . During a predetermined period, the magnitude of the variation is determined by comparing the variation with a reference value every time,
It becomes an index of the stability of the operation of the circuit including the SOI-MOSFET. When the variation of the threshold voltage exceeds a predetermined reference value, the stability of the circuit operation can be improved by fixing the body node to a constant potential. When the body nodes of all SOI-MOSFETs are floating and the variation of the threshold voltage does not exceed a predetermined reference value, formation of a body contact for fixing the potential of the body node is required. By omitting it, the degree of integration of the semiconductor integrated circuit can be improved, and the design resources of the bulk MOSFET can be effectively utilized.

SOI-M with large variation in threshold voltage
As a criterion for selecting an OSFET, for example, an average variation ΔV _th −
_ave may be used.

[0024]

(Equation 2)

Even if the variation of the threshold voltage falls within a predetermined range, the average variation ΔV _{th -ave} is compared with a reference value to obtain the average variation ΔV _{th -ave.
When the value of ave} is large, it can be determined that the operation of the circuit including the SOI-MOSFET is not very stable. In a semiconductor integrated circuit, an SOI
-The stability of the circuit operation and the improvement of the integration degree can be harmonized by selecting the MOSFET and the non-MOSFET and forming the body contact only on the one that does not satisfy the standard.

When the power supply voltage is V _DD , dV _th
By monitoring / V _DD , it is possible to select a device in which the rate of change in the threshold voltage becomes large at a low power supply voltage and a device in which the ratio does not become large. SOI-MOSFETs can be selected according to whether or not dV _th / V _DD exceeds a predetermined reference value. By forming a body contact only in a device exceeding the predetermined reference value, the stability of circuit operation and the degree of integration can be improved. Harmony of improvement.

It should be noted that the circuit analysis described in the above embodiment can be realized by a computer by causing a computer to read the circuit analysis program related to the circuit analysis described in the above embodiment from a recording medium storing the program. Needless to say.

[0028]

According to the method for analyzing a circuit of a semiconductor integrated circuit according to the first aspect of the present invention, or by performing a circuit analysis using a computer that reads a circuit analysis program stored in a recording medium according to the fifth aspect, SOI-MOSFET
Are automatically selected from those which do not satisfy a predetermined criterion for the threshold voltage, and the operation stability of the semiconductor integrated circuit can be easily evaluated.

According to the circuit analysis method for a semiconductor integrated circuit according to the second aspect, it is possible to automatically warn about a variation in the threshold voltage of the SOI-MOSFET exceeding a predetermined reference value, and to operate the semiconductor integrated circuit. There is an effect that the stability of can be easily improved.

According to the circuit analysis method for a semiconductor integrated circuit according to the third aspect, it is possible to automatically warn about an average value of the fluctuation amount related to the threshold voltage of the SOI-MOSFET exceeding a predetermined average value. There is an effect that the stability of the operation of the circuit can be easily improved.

According to the circuit analysis device of the fourth aspect, the threshold voltage of the plurality of SOI-MOSFETs in the circuit obtained by the circuit equation solving unit in the floating check unit can be automatically inspected, and the inspection result is obtained. Based on this, it is easy to determine whether to float the body node of the SOI-MOSFET, and it is easy to design a semiconductor integrated circuit with stable circuit operation.

According to the semiconductor integrated circuit of the sixth aspect,
SOI-MOSF with threshold voltage variation exceeding a predetermined reference value when body node is floating
An ET and a non-ET can be selectively provided with a body contact, and there is an effect that harmony between stability of circuit operation of the semiconductor integrated circuit and improvement in integration can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a circuit analysis device according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a circuit analysis method according to an embodiment of the present invention.

FIG. 3 is a graph for explaining an amount of change in a threshold voltage of an SOI-MOSFET.

FIG. 4 is a block diagram illustrating a configuration of a conventional circuit analysis device.

FIG. 5 is a flowchart for explaining a conventional circuit analysis method.

6 is a circuit diagram showing a model of an SOI-MOSFET used in the circuit analysis device shown in FIG. 4 and the circuit analysis method shown in FIG.

7 is a conceptual diagram showing data relating to a threshold voltage generated by the circuit analysis device shown in FIG. 4 and the circuit analysis method shown in FIG.

[Explanation of symbols]

1, 1A circuit analyzer, 2 input files, 3 data file input processing unit, 4, 4A circuit equation solving unit,
5 Waveform output unit, 6 Storage unit, 7 Floating check unit.

Claims (6)

[Claims] 1. A circuit analysis method for analyzing a circuit operation of a semiconductor integrated circuit including a plurality of SOI-MOSFETs, wherein the plurality of the plurality of semiconductor integrated circuits change momentarily during the operation of the semiconductor integrated circuit because a body node is floating. SO
Outputting data relating to a threshold voltage of the I-MOSFET; and outputting, from the plurality of SOI-MOSFETs, an SOI-MOSFET not conforming to a predetermined standard relating to a threshold voltage, based on the data relating to the threshold voltage. A method for analyzing a semiconductor integrated circuit, comprising: 2. The step of selecting the plurality of SOI-MOSFETs includes a step of comparing the amount of change in the threshold voltage with a predetermined reference value to select an SOI-MOSFET exceeding the predetermined reference value. 2. The circuit analysis method for a semiconductor integrated circuit according to claim 1, wherein: 3. The step of selecting the plurality of SOI-MOSFETs includes: comparing an average value of the amount of change in the threshold voltage with a predetermined average value;
3. The method for analyzing a circuit of a semiconductor integrated circuit according to claim 2, further comprising the step of: 4. A circuit analysis device for analyzing a circuit operation of a semiconductor integrated circuit including a plurality of SOI-MOSFETs whose body nodes are in a floating state, wherein a threshold voltage of the plurality of SOI-MOSFETs in the circuit is time-dependent. A circuit equation solving unit for calculating a change for each of the plurality of SOI-calculated by the circuit equation solving unit;
A circuit analysis device comprising: a storage unit that stores data relating to a threshold voltage of a MOSFET; and a floating check unit that checks threshold voltages of the plurality of SOI-MOSFETs based on the data stored in the storage unit. . 5. A computer-readable recording medium used when analyzing a circuit operation of a semiconductor integrated circuit including a plurality of SOI-MOSFETs by a computer, wherein the operation of the semiconductor integrated circuit is performed because a body node is floating. The plurality of SOs that change every moment
Based on the threshold voltage of the I-MOSFET, the plurality of S
A computer-readable recording medium storing a circuit analysis program for causing a computer to execute a process of selecting an SOI-MOSFET that does not conform to a predetermined threshold voltage standard from OI-MOSFETs. 6. A semiconductor integrated circuit including a plurality of SOI-MOSFETs, wherein the plurality of SOI-MOSFETs have a threshold in an operation of the semiconductor integrated circuit when body nodes of all SOI-MOSFETs are floating. The first voltage variation amount exceeding a predetermined reference value
In the operation of the semiconductor integrated circuit when the body nodes of all the SOI-MOSFETs are floating, the second SOI-MOSFET in which the amount of change in the threshold voltage does not exceed the predetermined reference value Wherein the first SOI-MOSFET has a body contact, and the second SOI-MOSFET does not have a body contact.