JPS60157741A - Optical memory medium and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to optical storage media, and more specifically,
This invention relates to the design and manufacture of multilayer counting type optical storage media.

BACKGROUND OF THE INVENTION In the past few years, the storage density per unit area of storage media has increased significantly. Tape storage devices in the early 1960's had a storage density of only 2 bits/dc13 bits/1 nch").

The magnetic disk currently in use is 20.5 x 106
It can store up to bit/d (132 x 10' bits/1 nch2) and has a higher storage density in the case of plated magnetic media.

Compared to these, optical storage devices have a much higher storage density in the longitudinal direction, 93 x 106 bits/
It is possible to record up to CD (600X, 10' bit/1nch2).

Optical storage devices usually consist of a rotating disk or phonograph carrying a suitable optical storage medium.

During a write operation, input data is sequentially modulated by a semiconductor laser diode and output. The laser optically records patterned data onto the storage medium by creating symbols in the active layer of the rotating record plate. Since the coherent light beam can be focused into a very narrow area, the individual data signals and their tracks making up the data can be brought extremely close to each other. In fact, optical storage devices can typically store 40 times or more data per unit area than comparable magnetic disks.

During a readout operation, light generated by a gas laser device scans the rotating record plate. The reflected light is modified by a data signal and detected by a group of photodiodes.

The data file consists of tracks arranged concentrically with a spacing of 1 micron.

The position at which the writing laser beam or the reading laser beam is focused is set by position information obtained from reflected light that is functionally different from those laser beams.

A rotating record plate carries an optical storage medium whose optical properties vary with the wavelength of the incident light.

A particularly difficult problem arises when reading, writing and positioning operations are each performed at different wavelengths. 1
When an optical storage medium is used for only one function, the response of the storage medium to incident light of other wavelengths used for other functions must be considered.

The total number of track bands consisting of user data recording tracks formed concentrically on a rotating record plate is 700 or more.
5eek mechanism), it can be accessed by the first actuator.

When a desired track band is detected, a second actuator positions the laser beam at a desired track within the track band. Information regarding the precise position can be obtained by a separate laser beam that is functionally different from other laser beams.

(Problems to be Solved by the Invention) The rotating record plate is composed of a plurality of thin film layers each having different thicknesses, each having a reflective property, a transparent property, an optically active property, or a light-absorbing property. On the other hand, the selection of various thin film layers to obtain the optimum characteristics is carried out through repeated trial and error.

The materials used to manufacture such storage devices are very expensive and the manufacturing process is complex, making trial-and-error work for every wavelength difficult and requiring a lot of effort. It requires cost and time.

(Means for Solving the Problems) A first object of the present invention is to select a plurality of materials for making an optical storage medium and a sequence of thin film layers formed by them to have optimal properties. An object of the present invention is to provide a method for designing an optical storage medium.

A second object of the invention is to enable the multilayer optical storage medium to store and reference the optical properties of preselected materials over a range of wavelengths. The object of the present invention is to provide a device for achieving desired optical characteristics for a specific wavelength.

A third object of the present invention is to take advantage of the high speed and capabilities of modern computer technology to allow the design of optical storage media consisting of a plurality of different thin film layers when a large number of wavelengths are applied. It is to be.

A fourth object of the present invention is to design an optical storage medium comprising a plurality of thin film layers comprising one or more optically active layers with optimal optical properties for a plurality of applied wavelengths, And it's about assembling.

The aforementioned object is achieved by an optical storage medium in which a plurality of wavelengths of light can be used separately, the sensitivity of the storage medium being such that an optically active layer therein is sensitive to the wavelength for writing. The quality of the readout signal is a function of the maximum energy it absorbs, the quality of the readout signal is a function of the optical properties for the readout wavelength, and the performance of the storage medium in writing and readout operations is a function of the optical properties for the position detection wavelength. It can be thought of as

According to the present invention, the method for manufacturing the optical storage medium consisting of a plurality of thin film layers stacked on a reflective substrate includes the steps of selecting the material of each thin film layer and the thickness of each thin film layer. a step of calculating optical characteristics for each of the wavelengths when the respective thin film layers are integrated; and a step of calculating the optical characteristics of the storage medium for each of the wavelengths in all cases of the plurality of wavelengths. To measure optical properties,
a step of repeatedly performing the calculation for a plurality of thicknesses; and a step of selecting a combination of thicknesses of each thin film layer so as to obtain optimal optical characteristics for each of the plurality of wavelengths. and assembling the optical storage medium of thin film layers having a thickness determined by the selection.

Furthermore, according to the invention, each selection and calculation step in the aforementioned method is facilitated by the use of a computer to determine the properties of the material of each thin film layer in a suitable When input into the program, calculation results can be obtained for each predetermined wavelength. These calculation results are printed on a list or displayed graphically.

More specifically, in accordance with the present invention, for the plurality of materials used in the thin film layers of the multilayer structure formed on the reflective layer, the identification labels of each material and their 200 nanometer (109 meter) Various data including optical constants at each wavelength set every 10 nanometers within the range from 900 nanometers to 900 nanometers is stored in the computer. By performing linear interpolation between the stored values, a value for the desired wavelength can be obtained.

In actual work, according to the combination of materials for each thin film layer constituting a specified multilayer body, the thickness of each thin film layer according to the specified combination and the material name of each thin film layer are sequentially input. The thickness and optical constants of each thin film layer are calculated using a mathematical model that determines the optical properties of the multilayer optical storage medium for a particular wavelength. The said calculation is
This is repeated for each wavelength of the multiple wavelengths used in the optical storage device according to the invention. The final calculation results are the reflectance, phase and absorption of the reflected light in each thin film layer of the multilayer as a function of the applied wavelength.

In this way, by entering data for various sequences of thin film layers, each with different thicknesses, it is possible to determine the optimal configuration for multiple wavelengths that is as close as possible to the desired response. can.

Furthermore, according to the present invention, an optical storage medium consisting of a multilayer body of thin film layers can be manufactured such that it has optimal optical properties for a plurality of different incident wavelengths.

(Example) Hereinafter, the present invention and its objects will be more clearly explained with reference to the accompanying drawings.

FIG. 1 illustrates the configuration of a multilayer body used in an optical storage medium according to the invention.

As shown, the multilayer body comprises a substrate (IO), a first layer (12) made of aluminum, for example, a second layer (14) made of silica, and a third layer acting as an active layer. (16) and a fourth layer (18) made of dielectric material.
) and a fifth layer (20
).

For information on these thin film layers and their optical properties, see 19
U.S. Pat.
5structure Involving In-5
itu Chemical Reaction in t
It is disclosed in detail in he Active 5 structure). Rights in this U.S. patent application are assigned to the assignee of this application.

Although the number of thin film layers shown in FIG. 1 is five, in theory any number of thin film layers may be used according to the present invention. In practice, the optical storage medium may consist of 5 to 20 layers.

To achieve the objectives of the present invention, an optimal optical storage device has the following optical properties: That is, the absorption must be at a maximum for the wavelength of the writing laser, the reflectance must be approximately 15% for the wavelength of a focus detection laser using, for example, a helium-neon laser, and the laser The reflectivity is low for the wavelength used to determine the course access search position for positioning within the track band.

For example, the write wavelength is 820-850 nanometers (109 meters), the readout and focus detection wavelength is 633 nanometers (109 meters), and the course access search wavelength is 790 nanometers (109 meters). ) lasers with three different wavelengths are used. Although these parameters and wavelengths can take various values, they are the optimum values insofar as they are limited to the characteristics of the present invention.

From this, it can be seen that three types of wavelengths, which differ from each other by a few tens of nanometers, are applied to the same optical storage medium. Therefore, it is a necessary condition that the spectral characteristics be optimal for all three types of wavelengths.

To determine the optical properties, certain reference values are used in a multilayer structure model of theoretical thin film layers.

According to the invention, a multilayer structure of thin film layers is assembled on a predetermined substrate, for example made of aluminum.

Furthermore, according to the invention, there can be any number of thin film layers. The parameters that determine the optical properties of said multilayer structure of thin film layers are the physical thickness and optical constants of each thin film layer.

Optical constants defined in conventional thin film optical theory are used in the mathematical model according to the invention.

Two parameter values are used, denoted n and k.

Here, the parameter n is the refractive index of the ordinary ray part in birefringence, and the parameter is the refractive index of the extraordinary ray part. The refractive index of each material changes depending on the wavelength of incident light.

The thickness and optical constants of each thin film layer determine three relevant optical properties of the multilayer they constitute. The first is the reflectance of the multilayer as a function of the wavelength of the applied light.

The second property is the absorption of laser light in the active layer as a function of the wavelength of the applied light. Third
is the phase of the reflected light with respect to the incident light, which is also expressed as a function of the wavelength of the applied light.

For each material selected, optical constants are stored in each table in the mathematical model every 10 nanometers in the range 200 nanometers to 900 nanometers. The program employs optical constants obtained from one of two data sources for a particular thin film layer.

If a numeric value is provided by the operator specifying any thin film layer of the multilayer body, that numerical value is used. On the other hand, if no numeric value is given, the program looks up the appropriate number from its internal table.

A linear interpolation is performed between the stored numerical values.

Based on the basic principles described above, the design of an optical storage medium consisting of multiple thin film layers formed on a reflective substrate involves the process of selecting the material for each thin film layer and A step of calculating the overall optical characteristics when the respective thin film layers are integrated, and repeating the calculation while varying the thickness of each of the thin film layers, and calculating the optical characteristics of each of the plurality of wavelengths for all cases of the plurality of wavelengths. measuring the optical properties of the storage medium with respect to wavelength; and selecting, for all of the plurality of wavelengths, a combination of thicknesses of each thin film layer that provides the optimum optical properties for each wavelength. and manufacturing the optical storage medium such that each thin film layer has a thickness determined by the selection.

The sequence of each step according to the present invention is shown in FIG.

As shown, data is entered into the computer in a user-friendly interactive sequence. According to said sequence, the wavelength, angle of incidence and polarization state of the light used are first required. The wavelength can be described for any desired storage device, provided the thickness of each thin film layer of the multilayer is described. The angle of incidence is described in degrees, and the polarization state is described as either S-polarized, P-polarized, or circularly polarized.

For each thin film layer of the multilayer, the identification label, n value, k value, and thickness of the material from which it is formed are entered into the computer. For a thin film layer made of a material for which all optical constants are stored in advance in the model, n and k are indicated, for example, with an asterisk. This supports that when calculating the optical properties of a multilayer body of thin film layers, the model should retrieve values from its internal table for those thin film layers marked with an asterisk. It is for.

An example of a screen displaying the input state of the model data is shown below for reference.

MATERIAL THICKNESS N Ksil
ica 8001.32 When all the data is input, the calculation result will be displayed in response to the rRUNJ command. The reflectance, transmittance, and phase shift in reflection of a multilayer body for a specific wavelength are
The absorption rate of each thin film layer of the multilayer is generated and displayed.

An example of a screen displaying the results of the calculations performed on the four thin film layers on the substrate is shown below for reference.

Kuchi-kun ΣRαm = run for d(21= 10 SY105YNONY: PI(ASE 3COMP
[Jr Engineering NG,,.

S P Co) LA Snow 4 Flood Open ■ Leap 0.0564370.056437
0.056437mmMANIll: Judging from this screen, the thickness and material of a predetermined number of thin film layers formed on the substrate are selected, thereby determining the optical properties of the thin film layers for a specific wavelength. Understand the process.

The above calculations are repeated for various configurations until a configuration is found that exhibits a response as close as possible to the desired response for each expected wavelength.

In order to change the thickness of a specific thin film layer and display the optical properties for a specific wavelength as a function of the thickness,
It is also possible to instruct a computer.

It is also possible to simultaneously change the thickness of each of a set of thin film layers constituting a multilayer body and observe the resulting spectral response.

The phase of the reflected light wave can also be analyzed by displaying the coordinates as shown in FIG. 4, 13.

The above program uses IBM's VM.
/CMS processing system, it is clear that the same objectives can be achieved using other equivalent computer systems.

Attached Document A shows the mathematical model or algorithm used to calculate the optical response. This mathematical model is an example of a formula for calculating the optical properties of an optical storage medium for each wavelength used.

In addition, in the attached separate manual B, in order to input the various data mentioned above and perform calculations based on a mathematical model so that appropriate optical characteristics can be obtained,
and all uses of the programs created to cause the resulting data to be displayed graphically are described.

Once the appropriate materials and thicknesses have been selected for each thin film layer, a multilayer of each of those thin film layers is then manufactured. Each thin film layer is successively deposited by sputtering or vapor deposition on a substrate of a suitable material to complete the multilayer. The thickness of each thin film layer is precisely controlled by known techniques.

With reference to the multilayer body consisting of five layers shown in the first diagram, a plurality of
In particular, one embodiment of an optical storage medium having optimal optical characteristics for three types of wavelengths will be described. This embodiment of the optical storage medium according to the invention constitutes a multilayer body consisting of thin film layers of the materials and thicknesses shown in Table 1.

Table 1 In such a configuration, 820 nanometers, 63
Optimal optical properties are obtained for three wavelengths: 2.8 nanometers and 790 nanometers. Table 2 shows the numerical values for each thin film layer in the state configured in this way.

Table 2 It is clear that the present invention is not limited to the technical scope shown by these Examples, and can be implemented with various changes or modifications.

One manual A- 07,2J″9

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a multilayer thin film structure according to the present invention. FIG. 2 is a flowchart representing the sequence of processing performed in the selection process according to the present invention. FIG. 3 is an example of data graphed based on calculation results regarding optical characteristics according to the present invention. FIG. 4 is another example of data graphed in the same manner as FIG. (10) Base (12) First layer, reflective layer (14) Second layer, phase layer (16) Third layer, active layer (18) Fourth layer, matrix layer (20) Fifth layer, protective coatingゝ-X < o o o o o chi cs o θ
な褌じ≧TAnanami艷 01% Continued from page 1 0 Inventor: Fred Sponzo United States of America, United States of America Roach Drift 0 Inventor: Franklin Cork United States of America, United States of America, United States of America, United States of America, United States of America, United States of America, United States of America, United States of America, United States of America, United States of America, United States of America, United States of America, United States of America, United States of America
208 1 Colorado 80302 Boulder No:I
3100 Number 212 Procedural Amendment Form) February 28, 1985 Manabu Shiga, Commissioner of the Japan Patent Office1, Indication of the case 1984 Patent Application No. 1949332, Name of the invention Optical storage medium and its manufacturing method 3 , Relationship to the case of the person making the amendment Patent applicant name Strain Technology Corporation 4, Agent 5, Date of amendment order January 9, 1985 (Shipping date January 29, 1985) 6. Subject of amendment ( 1) Applicant's column in the application (2) Agent's column (3) Power of attorney and its translation (4) Detailed explanation of the invention and brief explanation of the drawings in the specification (5) Drawing 7, Contents of the amendment (1) (2) (3) (4) As shown in the attached sheet (5) Engraving of the drawing (no change in content)

Claims (8)

[Claims] (1) a base, a first layer on the base constituting a phase layer, a second layer on the first layer constituting an active light absorption layer, and a second layer on the base constituting another phase layer; It consists of the third layer of
An optical storage medium in which the thickness and configuration of each layer are selected such that the optical properties thereof are optimal for a plurality of wavelengths. (2) The optical storage medium according to claim (1), wherein the optical properties are optimal for three different wavelengths. (3) Optical storage consisting of a plurality of thin film layers stacked on a reflective substrate, capable of separately using a plurality of wavelengths of light, and having performance as a function of optical properties for each said wavelength. A method for manufacturing a medium, comprising: a process of selecting a material for each of the thin film layers, a process of selecting a thickness of each of the thin film layers, and a process of selecting a material for each of the thin film layers, and a process of selecting a material for each of the wavelengths when the thin film layers are integrated. calculating optical properties; and repeating said calculations for a plurality of thicknesses in order to measure the absorption of light by said optical storage medium for each of said plurality of wavelengths. and a step of selecting a combination of thicknesses of the respective thin film layers so as to obtain optimal optical characteristics for each of the plurality of wavelengths in all cases of the plurality of wavelengths, and a step of selecting the thickness combination determined by the selection. assembling said optical storage medium comprising thin film layers comprising: (4) The materials of the thin film layer each have a plurality of associated optical constants, and for the plurality of selected materials,
The optical constants are stored in a computer, the computer is searched for the optical constants based on the identification label attached to each material, and the optical properties for each wavelength are determined based on the optical constants obtained thereby. 3. A method according to claim 3, characterized in that: (5) The method according to claim (3), wherein the optical properties are calculated based on Fresnel's interference theory regarding the optical properties of a thin film multilayer structure. (6) For wavelengths in the range of 200 nanometers to 900 nanometers, a plurality of different materials, each having a plurality of A method according to claim 3, characterized in that the optical properties are calculated by using a computer in which optical constants are stored. (7) A method for adjusting a thin film multilayer body containing a light reflective material and a light absorbing material, the method comprising: adjusting the optical properties of each thin film layer constituting the thin film multilayer body for a plurality of wavelengths of incident light; measuring based on the thickness of each thin film layer for each wavelength; adjusting the thickness of each thin film layer for each wavelength so as to be as close to a predetermined spectral characteristic as possible; assembling a thin film multilayer of a predetermined material, each of said thin film layers having a thickness selected to most closely approximate a desired spectral response for each of said wavelengths. (8) A method for manufacturing an optical storage medium consisting of a plurality of thin film layers constituting a thin film multilayer stacked on a reflective substrate, the method comprising the steps of: The process of calculating the optical thickness and for each wavelength,
The method includes the steps of selecting the thickness of each of the thin film layers so as to obtain a desired optical response, and assembling the thin film multilayer body based on the thickness of each of the thin film layers so selected. Method. (Engraving of the following 4 unit specifications (no changes to the contents)