JPH02177036A - Multivalued memory element - Google Patents

Abstract

PURPOSE:To obtain a large capacity with a simple and small-sized structure by forming information pits of an optical memory as a multivalued information memory. CONSTITUTION:The multivalued memory element is formed by laminating a magnetic material 12 consisting of, for example, TbFeCo and an insulator layer 11 consisting of ZnS which is transparent to, for example, the light with which the layer is irradiated. The plural information pits 13, 14 are formed on this element and the element has the thickness corresponding to the information. The peak of the rotating angle of the plane of polarization appears at a certain wavelength when the element is irradiated with light form the layer 11 side while the wavelength is scanned. Since the thickness of the layer 11 varies with the pits 13 and 14 in this case, the number of the wavelengths indicating the peak varies. The number of the wavelengths indicating the peak can be changed by adjusting the thickness, by which the multivalued memory can be formed. The information quantity per unit area is extremely increased in this way and since the element is constituted by laminating the magnetic material and the insulator of the thickness varied according to the sections, the extremely simple structure is obtd.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a ROM that can record multilevel information using magneto-optical effects such as Kerr effect and Faraday effect.
and other memory devices.

[Prior art and problems to be solved by the invention] Conventionally,
As ROMs (read only memories), those made of semiconductors and those that form bits (such as CDs) are known. However, these usually have a signal of "1".
This is a binary ROM that is recorded in binary values of "0" and "0".

On the other hand, in response to the demand for higher density memory, attempts are being made to realize multilevel ROMs. For example, in semiconductors, multilevel ROMs have multiple gates and multiple charge distributions.
is being realized.

However, such a multilevel ROM ultimately becomes a binary ROM.
Since this is just a combination of M, there are drawbacks such as the area of the unit ROM becoming large and the addition of a power supply voltage distribution circuit.

This invention was made in view of such circumstances, and
It is an object of the present invention to provide a multilevel memory element that is small in size and has a simple structure.

[Means for Solving the Problems] A multi-level memory element according to the present invention includes a magnetic material and an insulating layer formed on the magnetic material and transparent in the wavelength range of the irradiated light. The insulating layer has a plurality of information recording parts having a thickness according to the information, and the number of peaks of the rotation angle of the polarization plane of these recording parts is used as data. The plane of polarization of linearly polarized light irradiated onto a magnetic material rotates when it passes through the magnetic material and when it is reflected by the magnetic material, which is known as the Faraday effect and the Kerr effect. has a peak when the irradiating light has a certain wavelength. The number of peaks, that is, the number of wavelengths at which the peaks appear, differs depending on the thickness of the insulating layer on the magnetic material. Utilizing this fact, multi-value information can be recorded.

[Example] This invention will be described in detail below. FIG. 3 is a diagram for explaining the invention in detail.

Reference numeral 1 in the figure indicates the atmosphere or vacuum, in which a laminate consisting of a transparent insulating thin film 2 (thickness d) and a magnetic material 3 in an ordered state exists. The reflectance on the insulator side at the interface between the insulator thin film 2 and the atmosphere 1 is RZI2, and the reflectance on the insulator side at the interface between the insulator thin film 2 and the magnetic material 3 is RL.
3Z, RZ3λ is a complex number, and the product of these is given by the following equation (1).

RL, 2 ΦR23□ Trout δe′ ・・・・・・・・・
......(1) Here, δ is the absolute value of R,, L* R,,2, and ψ is the argument angle of R2LIZ '' Rz3x. Note that ψ is generally a negative value. Become.

In this case, if multiple reflections in the insulator thin film 2 are considered, the rotation angle of the plane of polarization due to the magneto-optic effect has a peak at a specific wavelength. The wavelength at that time is λ. When L is the effective film thickness for binding and light, the following (2) holds true.

λn −L/ C2yrn−ψ) (n−0,1,
2゜・・・oo)・・・・・・・・・(2) Here, ψ is the value given by equation (1), and L is the refractive index ntz of the insulator with respect to the atmosphere and the insulator thin film 2. It is expressed by the following equation (3) using the thickness d.

L-4πdJ Possible T: Punishment Goat...(3)
Here, φ is the angle of incidence on the stack.

The above λn is in the visible light region (wavelength is 300 nm-900 nm)
r+a+), from (2), the following (
4) It is necessary to satisfy the formula.

300<L/(2πn+ψ)<900−・−・・
... (4) The following equation (5) is derived from this equation (4).

(1/2π) ((L/900)−1ψ1)<n<
(1/2 π) f (L/300)
−lψ1 ) ... ... (5) Therefore, by appropriately setting the value of L, multiple n
Equation (5) can be made to hold for .

Here, 1ψ1 can be approximately regarded as 0 in actual materials, so in equation (5), the maximum value of n (nl.8) and the minimum value of n (nI, r ,
l) and the number of peaks of the rotation angle of the plane of polarization are shown in Table 1 for each range of L.

Table 1 As described above, by setting L within a certain range, the number of peaks of the rotation angle of the plane of polarization, that is, the number of wavelengths at which the peaks appear can be arbitrarily determined.

Therefore, by changing the thickness of the insulating thin film, it is possible to set the number of peaks of the rotation angle of the plane of polarization according to the thickness. This means that the information per bit is multivalued.

Next, a multilevel memory device according to an embodiment of the present invention will be specifically described.

FIG. 1 is a sectional view showing a multilevel memory element according to a first embodiment. This element is constructed by laminating a magnetic material 12 made of, for example, TbFeCQ, and an insulating layer 11 made of, for example, ZnS and transparent to irradiated light. This element is formed with a plurality of information bits (only two bits 13 and 14 whose insulator layers have different thicknesses are shown in FIG. 1), and each of these bits has a thickness corresponding to the information. are doing.

When the information bits of the memory element configured in this manner are irradiated with light from the insulator layer 11 side while scanning the wavelength, a peak of the rotation angle of the plane of polarization appears at a certain wavelength, as described above. In this case, for example, bit 13
As shown in FIG. 1, the thickness of the insulating layer is different between the two types, and therefore the number of wavelengths at which the peak of the rotation angle of the polarization plane appears is different, as described above. In this case, by appropriately adjusting the thickness, the number of wavelengths exhibiting a peak can be changed arbitrarily, so a multilevel memory can be formed.

Next, a second example will be described. FIG. 2 is a sectional view showing a memory element according to a second embodiment. The memory element according to this embodiment includes a magnetic material 22 and an insulator 21 laminated thereon, and further includes a plurality of recording bits (24 and 25 in FIG. 2) on the surface of the insulator layer 21. An opaque layer 23 made of metal, semiconductor, or the like is provided in a portion other than those shown in ). This opaque layer 23
has a function of reducing background information other than recording bits, that is, noise.

In this second embodiment as well, a multilevel memory can be formed in exactly the same manner as in the first embodiment.

[Effects of the Invention] According to the present invention, since the information bits in the optical memory are multilevel information memory, the amount of information per unit area can be extremely increased. As a result, it is possible to obtain a memory element that is small in size but has a large capacity. Moreover, since it is constructed by laminating a magnetic material and an insulating material whose thickness varies depending on the portion, the structure is extremely simple. Therefore, there is an advantage that even if the memory deteriorates, it can be repaired very easily.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing a multilevel memory element according to an embodiment of the invention, and FIG. 3 is a diagram for explaining the invention in detail. 11.21; Insulator layer, 12, 22; Magnetic material, 13.1
4, 24, 25; information bit; 23; opaque layer. Figure 1 Patent applicant Casio Computer Co., Ltd. Figure 2

Claims (1)

[Claims] A multilevel memory element comprising a magnetic material and an insulating layer formed on the magnetic material and transparent in the wavelength range of the irradiated light, the insulating layer comprising a plurality of layers having a thickness depending on information. 1. A multi-valued memory element having information recording parts and using the number of peaks of polarization plane rotation angles of these recording parts as data.