Data processing: structural design – modeling – simulation – and em – Simulating electronic device or electrical system – Target device
Reexamination Certificate
1998-07-23
2001-12-04
Teska, Kevin J. (Department: 2123)
Data processing: structural design, modeling, simulation, and em
Simulating electronic device or electrical system
Target device
C703S002000
Reexamination Certificate
active
06327558
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The entire disclosure of Japanese Patent Application No. Hei 9-360753 filed on Dec. 26, 1997 including specification, claims, drawings and summary are incorporated herein by reference in its entirety.
BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates to a simulation apparatus for a ferroelectric device, more specifically an apparatus for simulating dynamic characteristics of a circuit including a ferroelectric memory device.
2. Description of the Related Art
It is known that a ferroelectric device shows a hysteresis in a relation between applied voltages and polarization charges. The ferroelectric device can be used as an nonvolatile type semiconductor memory or other devices by utilizing the electric characteristic. In this connection, the hysteresis of the ferroelectric device need to be evaluated quantitatively in case of using the ferroelectric device to a memory or other circuits.
In order to evaluate the hysteresis of the ferroelectric device quantitatively, a method presented on the JAPANESE JOURNAL OF APPLIED PHYSICS Volume 30, Number 9B page 2384 to 2387 issued on September, 1991 as a “Simulations of Ferroelectric Characteristics Using a One-Dimensional Lattice Model” under the name of OMURA et. al. can be used.
The method uses a simulation model utilizing an overall free energy “f” defined as an equation shown in below,
f=&Sgr;
n=1, N
{&agr;/2·
p
n
2
+&bgr;/4·p
n
4
+k/
2·(
p
n
−p
n−1
)
2
−p
n
·e}
In the equation, P
n
shows a dipole moment of the n th lattice, k is an interaction coefficient of atoms located adjacently, e means an electric field and the equation satisfies a condition of &agr;<0, &bgr;>0. Also, &agr; can be shown in a numerical formula shown in below as a function of temperature T,
&agr;=a
(
T−T
0
)
wherein a condition of a>0 must be satisfied, and T
0
shows the Curie temperature. In addition, an equation shown in below is the equation for defining symbols in the above equation calculating the simulation model utilizing the overall free energy “f”,
&Sgr;
n=1, N
{X
n
}=X
1
+X
2
+ . . . X
N
The hysteresis of the ferroelectric device will be evaluated quantitatively in accordance with the overall free energy “f” thus calculated.
However, the simulation method described above has the following problems to be resolved. The equation shown in above which describes physical phenomena under atomic basis is used as the simulation model in the conventional simulation method. Therefore, it is not appropriate to use the equation for describing phenomena caused under electric basis. Also, complication of the equation make hard to understand the equation itself at sight. As a result, it is not-easy to use the simulation results on engineering basis such as circuit analysis or the like. In addition, a computer having higher processing capabilities is required when the equation is calculated by the computer because the equation itself is complicated.
Further, in order to increase an operation speed of the ferroelectric memory or similar devices, it is necessary to evaluate not only the hysteresis of the ferroelectric device quantitatively but also quantitatively evaluate dynamic characteristics of a circuit including the ferroelectric device such as transient responses. The simulation model described above can not be used for simulating the dynamic characteristics of the circuit on engineering basis because the calculation is too complex to carry out.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a simulation apparatus capable of easily evaluating dynamic characteristics of a circuit including a ferroelectric device quantitatively.
In order to apply a simulation model to a practical ferroelectric device, specific constants such as characteristic constants realizing a simulation model need to be determined. Eventually, it is hard to apply the simulation model to the practical circuit using the ferroelectric device when determination of the characteristic constants is difficult to carry out. Further, it is another object of the present invention to provide an apparatus for extracting the characteristic constants of the ferroelectric device easily.
In accordance with the present invention there is provided an apparatus for simulating electrical characteristics of a circuit including a ferroelectric device, the apparatus calculating dynamic characteristics of the circuit in accordance with a hysteresis representing a relationship between voltages applied to the ferroelectric device and polarization charges charged in the ferroelectric device, the apparatus comprises:
first means for determining a without-polarization reversal term at least a part of which as a saturation function, the without-polarization reversal term corresponds to phenomena not accompanying with reversal of spontaneous polarization of the ferroelectric device in the hysteresis,
second means for determining a with-polarization reversal term at least a part of which as a saturation function, the with-polarization reversal term corresponds to phenomena accompanying with reversal of spontaneous polarization of the ferroelectric device in the hysteresis, and
third means for determining dynamic characteristics of the circuit including the ferroelectric device in accordance with the hysteresis of the ferroelectric device composing of both the without-polarization reversal term and the with-polarization reversal term.
In another aspect, the present invention provide a method for simulating electrical characteristics of a circuit including a ferroelectric device, the method is characterized by calculating dynamic characteristics of the circuit in accordance with a hysteresis representing a relationship between voltages applied to the ferroelectric device and polarization charges charged in the ferroelectric device, the method comprises the steps of:
determining a without-polarization reversal term at least a part of which as a saturation function, the without-polarization reversal term corresponds to phenomena not accompanying with reversal of spontaneous polarization of the ferroelectric device in the hysteresis,
determining a with-polarization reversal term at least a part of which as a saturation function, the with-polarization reversal term corresponds to phenomena accompanying with reversal of spontaneous polarization of the ferroelectric device in the hysteresis, and
determining dynamic characteristics of the circuit including the ferroelectric device in accordance with both the without-polarization reversal term and the with-polarization reversal term.
Further, in accordance with the present invention there is provided a program storage medium readable by a machine, the machine performs procedures for calculating dynamic characteristics of a circuit including a ferroelectric device based on a hysteresis representing a relationship between voltages applied to the ferroelectric device and polarization charges charged in the ferroelectric device in accordance with a program stored in the program storage medium, the program is characterized by comprising the steps of:
determining a without-polarization reversal term at least part of which as a saturation function, the without-polarization reversal term corresponds to phenomena not accompanying with reversal of spontaneous polarization of the ferroelectric device in the hysteresis,
determining a with-polarization reversal term at least a part of which as a saturation function, the with-polarization reversal term corresponds to phenomena accompanying with reversal of spontaneous polarization of the ferroelectric device in the hysteresis, and
determining the dynamic characteristics of the circuit including the ferroelectric device in accordance with both the without-polarization reversal term and the with-polarization reversal term.
In another aspect, there is provided an apparatus for extracting characteristic constants of a ferroelectric device used for
Frejd Russell W.
Merchant & Gould P.C.
Rohm & Co., Ltd.
Teska Kevin J.
LandOfFree
Apparatus for simulating electrical characteristics of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for simulating electrical characteristics of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for simulating electrical characteristics of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2578727