JPS63153748A - Ferroelectric storage device - Google Patents

Abstract

PURPOSE:To prevent the reduction in the impedance attended with the increased capacity by connecting a storage section under read operation selectively to an amplifier CONSTITUTION:Upper electrodes 1a, 1b... isolated electrically, a lower electrode 2 connected to ground via a contact 15 and a ferroelectric thin film 3 among the electrodes 1a, 1b-2 are provided to disk support 10 driven a shaft 11. The storage control of the film 3 is read by the selection connection to a readout amplifier via a common electrode 13 and a contact 15 of a storage section selecteicted by the projection of a selection circuit device laser light 14 to selection circuit 12a, 12b... corresponding respectively to the electrodes 1a, 1b.... Thus, the decrease in the input impedance attended with the increased capacity is prevented and increase in noise and unstable read are evaded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a memory device using a ferroelectric polymer thin film.

(Prior Art) As shown in FIG. 4, the information storage part of a ferroelectric memory device consists of a ferroelectric thin film 3 sandwiched between two electrodes 1 and 2. Erasing, writing, and reading data in a storage device are performed as follows.

i) Erasing: As shown in FIG. 5a, an electric field larger than the coercive field of the ferroelectric thin film 3 is applied to the ferroelectric thin film 3 by the power source 4 to align the polarization of the thin film in one direction.

ii) Writing: As shown in FIG. 5b, the thin film 3 is locally heated with the laser beam 5 while applying an electric field below the coercive electric field of opposite polarity to that during erasing to the thin film 3.

As the coercive electric field decreases due to temperature rise, the polarization of only the irradiated area is reversed.

iii > Readout: As shown in Fig. 5c, the surface of the thin film 3 is scanned with a laser beam spot 5 weak enough not to cause an irreversible polarization change, and the pyroelectric current at the irradiation point is transmitted to the current amplifier 6 and the signal processing connected thereto. The system 7 detects and reads the polarity of polarization.

The ferroelectric thin film 3 may be made of vinylidene fluoride/ethylene trifluoride copolymer.

(Problem to be solved by the invention) A thin film with a thickness of 1 μm used as a memory element is 1 c
It has a capacitance of about 20 nF per station. When the area is increased to configure a large capacity memory, the capacitance increases proportionally and the impedance decreases. In general, when the impedance at the input terminal of a current amplifier for information detection decreases, noise increases and instability occurs.

(Means for solving the problem) The above problem is solved by selecting the information storage section made of a ferroelectric thin film and the part of this information storage section where the readout operation is performed as the readout signal amplifier. The problem is solved by a ferroelectric memory device comprising a switching means for connecting the two.

(Functions and Effects) Of the information storage section made of a ferroelectric thin film, the part of the information storage section where the reading operation is performed is selectively connected to the signal amplifier, so the signal amplifier's capacity increases due to the increased capacity. It is possible to prevent a decrease in input impedance, and it is possible to avoid an increase in noise and instability that accompanies an increase in capacity.

(Example 1) Hereinafter, the present invention will be described in detail based on Examples. 1st
Figures A and 1B are a plan view and a sectional view, respectively, of a first embodiment of the present invention. The disk support 10 is the shaft 11
rotated by This disk support 10 is provided with a ferroelectric thin film 3 sandwiched between an upper electrode 1 and a lower electrode 2. The upper electrodes 1a, lb, and lc are electrically separated from each other, and are connected to the common electrode 13 via selection circuits 12a, 12b, and 12c provided radially inside, respectively.
It is connected to the. Selection circuits 12a, 12b.

12C is constituted by an element whose gate is turned on and off by light, such as a photoconductor or a light-controlled thin film transistor. A laser beam spot 5 for writing and reading and a laser beam 14 for driving a selection circuit are attached to a disk support 100.
They are lined up in the radial direction. The writing/reading laser beam spot 5 moves in the radial direction when writing/reading data, so that a plurality of pieces of information can be successively recorded along the radial direction in one part of the information storage section.

When the write/read laser beam spot 5 is irradiated on the information storage section having the upper electrode 1b, the selection circuit driving laser beam 14 is located on the selection circuit 12b and irradiates it to read information. The upper electrode 1b of the information storage section is electrically connected to the common electrode 13. The common electrode 13 is connected to a current amplifier via a contactor 15, and information is detected.

In this way, the impedance of the memory element can be increased by the number of electrode divisions.

(Embodiment 2) FIGS. 2A and 2B are a sectional view and a plan view of a second embodiment of the present invention. A ferroelectric thin film 3 sandwiched between a lower electrode 2 and a plurality of upper electrodes 1a, 1blc, and ld is provided on a card-shaped support 10. Upper electrode la, l
b, lc, and ld are selection circuits 12a and 12b, respectively.
, 12C, and 12d to the common electrode 13. The selection circuits 12a, 12b, 12c, and 12d are photoconductors or light-controlled thin film transistors that become conductive when irradiated with light. When reading out information stored in the information storage portion of the portion including the upper electrode 1a, the upper electrode 1a is connected to the common electrode 13 by irradiating the selection circuit 12a with a laser beam 14 for driving the selection circuit. At this time, since the upper electrodes other than the upper electrode 1a are separated from the common electrode 13, a decrease in impedance can be avoided. If a plurality of information storage sections and selection circuits are arranged in parallel as shown in the figure, when the entire card is moved in the direction of the arrow shown in FIG. When the laser beam spot 10 is irradiated, the selection circuit driving laser beam 14 irradiates the selection circuit 12a,
A reading laser beam spot 5 is placed at the position of the upper electrode 1b.
When the selection circuit driving laser beam 14 is irradiated with the selection circuit 12b, the selection circuit 12b is irradiated with the selection circuit 12b, and there is no need to apply a signal for switching the electrodes from the outside.

In addition, in the first and second embodiments described above, in addition to using the selection circuit 12 based on optical control, a switching means for selectively bringing the contact 15 into contact with the upper electrode 1a of the information storage section that is being read is used. It can also be used.

(Example 3) FIG. 3 is a side sectional view of a third embodiment of the invention.

In this embodiment, the support body 10, the lower electrode 2, the selection circuit (photoconductor) 12, and the intermediate electrode 16a.

16b, 16c, 16d, ferroelectric thin film 3, upper electrode 1
are stacked in this order. Intermediate electrodes 16a, 16b,
16c and 16d are electrically separated from each other. During reading, a laser beam spot 5 for writing and reading is irradiated from above, and a laser beam 14 for selection is irradiated from the bottom of the area being read. This selection beam causes the selection circuit (photoconductor) 12 to conduct and the intermediate electrode 1
The impedance between the electrode 6a and the lower electrode 2 decreases, and only that portion is selected. Intermediate electrode 16a.

Even in the state where 16b, 16C, and 16d are removed, the ferroelectric thin film 3 at the position irradiated with the selection laser beam 14
Since only the end faces of the intermediate electrodes 16a, 16b, 16C are electrically connected to the lower electrode 2.

16d is not necessary in principle, but current concentrates on a part of the photoconductor, causing an increase in impedance, and writing and reading cannot be performed completely. By providing this intermediate electrode, the impedance with the lower electrode 2 is reduced, and writing and reading can be performed perfectly. Further, the support 10 and the lower electrode 2 need to be transparent.

In each of the above embodiments, the upper electrode may be made transparent so that the ferroelectric thin film itself absorbs the laser light and converts it into heat, or the opaque upper electrode may absorb heat and indirectly convert the ferroelectric thin film into heat. The thin film may also be heated. Further, it is preferable that the irradiation of the selection laser beam precedes the irradiation of the read/write laser beam spot to compensate for the time delay in conduction.

[Brief explanation of the drawing]

1A and 1B are a plan view and a sectional view, respectively, of a first embodiment of the present invention, FIG. 2A and 2B are a plan view and a sectional view, respectively, of a second embodiment of the present invention, and FIG. 3 is a plan view and a sectional view, respectively, of a second embodiment of the present invention. 4 is a sectional view showing the basic configuration of a conventional ferroelectric memory device, and FIGS. 5A, 5B, and 5C are respectively a side sectional view of a third embodiment of the present invention. A diagram explaining basic operations of erasing, writing, and reading. 1.1 a, 1 b, l C---...upper electrode, 2
... lower B electrode, 3 ... ferroelectric thin film, 4 ... power supply, 5 ... laser beam spot for writing and reading, 6 ... ...Current amplifier, 7...Signal processing system, 10...Support, 11...
... Axis, 12.12a, 12b, 12c, 12d--
---Selection circuit, 13...Common electrode, 1
4... Laser light for driving selection circuit, 15...
...Contactor, 16a, 16b, 16c, 16d...Intermediate electrode. Figure 1A Figure 1B Figure 2A Figure 2B Movement direction

Claims (1)

[Claims] A ferroelectric storage device comprising an information storage section made of a ferroelectric thin film, and switching means for selectively connecting a portion of the information storage section where a read operation is being performed to a read signal amplifier.