GB2069741A

GB2069741A - Reproducing stylus for information signal recording mediums of electrostatic capacitance type

Info

Publication number: GB2069741A
Application number: GB8004811A
Authority: GB
Original assignee: Victor Company of Japan Ltd; Nippon Victor KK
Current assignee: Victor Company of Japan Ltd; Nippon Victor KK
Priority date: 1980-02-13
Filing date: 1980-02-13
Publication date: 1981-08-26
Also published as: DE3005442A1; DE3005442C2; CH634164A5; GB2069741B; NL8000898A

Abstract

There is provided a reproducing stylus 15 for reproducing a signal from a recording medium 21 on which the signal has been recorded as variations in geometrical configurations. The stylus 15 comprises a body 31 and an electrode 33 formed on a surface of the body 31 for reproducing the signal from the medium 21 as variations in electrostatic capacitance corresponding to the variations in the geometrical configurations. The electrode 33 comprises a part of the body 31 rendered electroconductive by an ion-implantation process over a predetermined surface of the body 31 to a predetermined depth. <IMAGE>

Description

SPECIFICATION Reproducing stylus for information signal recording mediums of electrostatic capacitance type The present invention relates generally to reproducing styluses for information signal recording mediums of electrostatic capacitance type. More particularly, the invention relates to a reproducing stylus for reproducing, as variations in electrostatic capacitance, an information signal recorded as variations in geometrical configurations on a disc-shaped recording medium, which stylus has an electrode part formed on the stylus body thereof by an ion-implantation process.

In general, an information signal recording medium of electrostatic capacitance type, in one example thereof, has a construction comprising a recording medium structure made of a synthetic resin and having, formed on the surface thereof, variations of geometrical shapes made up of a plurality of pits in responsive accordance with an information signal, a thin film of an electroconductive metal formed by evaporation deposition on the surface of the recording medium structure, and a thin film of a dielectrice material formed in adhering state on the metal thin film. A reproducing stylus for relatively tracing this information signal recording medium of electrostatic capacitance type and reproducing an information signal recorded thereon has an electrode.

As a reproducing stylus having an electrode traces over the surface of a recording medium fabricated in this manner, the electrostatic capacitance between the electrode of the reproducing stylus and the metal thin film of the recording medium through the dielectric thin film or through the dielectric thin film and an air gap varies in response to the variation of the geometrical shape of the recording medium. The recorded signal is reproduced by a known method in response to this variation of the electrostatic capacitance.

The electrode of a reproducing stylus of this kind known heretofore has been formed as an adhering layer by depositing a metal such as tantalum, hafnium, or titanium by vacuum evaporation deposition or sputtering on a specific surface of a reproducing stylus body made of sapphire or diamond. Since the electrode of a known reproducing stylus of this character is formed as an adhering layer by vacuum evaporation deposition or sputtering of a metal on the surface of reproducing stylus body, it is easily peeled off from the stylus body during use. For this reason, the serviceable life of a known reproducing stylus of this type has been disadvantageously short, being of the order of several hours to 100 hours at the most.

Furthermore, since the wear resistances of the reproducing stylus body and the electrode are clearly different, in the action of wear of the stylus tip as it contacts the recording medium rotating at high speed, the stylus body and the electrode do not undergo mutually uniform wear. This is another reason why the known reproducing stylus cannot carry out good signal reproduction in a stable condition over a long period of time. Still another problem is the difficulty, during production, of depositing metal layers by evaporation deposition or sputtering all with the same thickness on large number of reproducing stylus bodies, whereby irregularities in the characteristics of the reproducing styluses disadvantageously occur.

Particularly in the case where diamond, which has high wear resistance, is used for the stylus body, it is difficult to deposit a metal thereon by evaporation deposition, and even when a metal layer electrode is thus formed, it is easily peeled off. On the other hand, when sapphire is used for the stylus body, the deposition of a metal layer thereon be evaporation deposition is easier than that on diamond, but sapphire has less wear resistance than diamond, whereby the life of the sapphire stylus is short.

In the production of the reproducing stylus according to the present invention, the electrode of the stylus is not formed by depositing a metal layer by a conventional technique such as evaporation deposition or sputtering but is formed as an electrode part on a specific face of the stylus body by an ionimplantation process.

That is, it is a general object of the present invention to provide a new and useful reproducing stylus for information signal recording mediums of electrostatic capacitance type in which the above described difficulties accompanying known reproducing styluses of like type have been overcome.

The present invention provides a reproducing stylus for reproducing an information signal from a recording medium on which said information signal has been recorded as variations in geometrical configurations, said reproducing stylus comprising a reproducing stylus body and an electrode part formed on a specific surface of the reproducing stylus body and functioning to reproduce the information signal recorded on the recording medium as variations in electrostatic capacitance reponsive to the variations in geometrical configurations, said electrode part comprising a part of the reproducing stylus body rendered electroconductive by carrying out an ion-implantation process over said specific surface to a specific depth from the outer surface.

Another and specific object of the invention is to provide a reproducing stylus for information signal recording mediums of electrostatic capacitance type which has an electrode part formed by ionimplantation of ions of a substance such as a metal, metalloid or semimetal, or a semiconductor. In accordance with the invention, an electrode part is formed on a specific face of a reproducing stylus body by imparting electroconductivity to the stylus body over that face to a specific depth from the outer surface by ion-implantation. For this reason, there is no possibility of peeling off of the electrode part.

Furthermore, since the electrode part wears evenly with the stylus body, the reproducing stylus can carry out good signal reproduction in a stable manner over a long period of use. Still another advantageous feature of the invention is that, in the quantity production of a large number of reproducing stylus bodies, their electrode parts can be formed uniformly to precisely the same depth, whereby reproducing styluses of uniform characteristics can be produced at low cost.

Other objects and further features of the present invention will be apparent from the following de- tailed description with respect to one embodiment thereof when read in conjunction with the accompanying drawing, in which: Figure 1 is a bottom perspective view of one example of a pickup cartridge in which the reproducing stylus according to the present invention can be applied; and Figure 2 is a greatly enlarged perspective view showing the extreme end part of one embodiment of the reproducing stylus according to the invention for information signal recording mediums of electrostatic capacitance type.

One example of a pickup cartridge in which a reproducing stylus according to the present invention can be applied will first be described with reference to Figure 1.The cartridge assembly 10 has a support plate 11, to the bottom surface of which a bracket 12 made of a ferromagnetic material is fixed.

A magnet plate 13 is provided on one downwardly extending surface of the bracket 12. A bipod-shaped cantilever 14 supports at its distal or free end a reproducing stylus 15, described hereinafter, fixedly mounted thereon. The bipod legs of this cantilver at its proximal or base end pass through and are fixed to a transverse bridge member 16. A magnet plate 17 is fixed to the rear surface of this bridge member 16.

The cantilever 14 is stably supported with respect to the support plate 11 by the magnetic attraction of the magnet plate 17 against the magnet plate 13. The reproducing stylus 15 has at a specific face thereof an electrode surface. One end of a lead wire 18 is connected this electrode surface by an electroconductive adhesive, while the other end of the lead wire 18 is connected to a terminal 19 provided on the lower surface of the support plate 11.

At the time of use of the cartridge, the cartridge 10 is loaded into an actuator section provided on a rotating cover (both not shown) of a carriage. When the rotating cover is closed, the terminal 19 becomes connected to the core conductor of a coaxial resonator provided in the carriage, whereupon the cartridge is placed in the state wherein signal reproduction can be carried out.

A pickup cartridge of this kind is described in detail in the specification of U.S. Patent No. 4,160,268, entitled "Signal pickup device with tracking control and jitter compensation for a video disc" which was assigned to the same assignee as in the present application.

The state of tracing of the reproducing stylus 15 relative to the information signal recording medium of electrostatic capacitance type of disc shape (hereinafter referred to simply as "disc") is indicated in Figure 2. This disc 21 is not provided with a guide groove but has a large number of pits formed on its surface in responsive correspondence to the recorded signal. Pits 22 are formed in the disc 21 in responsive accordance with the above mentioned main information signal. Only one part of the main information signal track turns comprising each of successions of pits 22 is shown. The tracks are those of a single spiral track and are respectively parts corresponding to revolutions of the disc 21. In the present embodiment of the invention, an informa tion signal of four fields of a video signal are recorded along the track.In the present embodiment of the invention, the pits are so formed that one of the edge lines of each track is substantially coinci dent with the nearest edge line of the adjacent track.

That is, the adjacent track are so formed that they are successively contiguous. Accordingly, the track pitch is substantially equal to the track width.

At central positions (coinciding with the edge lines of the tracks in the present embodiment of the invention) approximately intermediate between the centerlines of the mutually adjacent tracks pilot signal pits 23 and 24 responsively corresponding to pilot signals of the different frequencies are formed.

An arrangement of the pits of this kind is described in detail in the specification of British Patent Application No. 14533/77, entitled "Information signal recording system", of which applicant is the same as of the present application.

The disc 21 comprises a polyvinyl chloride resin disc structure 25 on the upper surface of which the pits 22, 23, and 24 are formed, an aluminum foil layer 26 adhering to the upper surface of the disc structure 25, and a dielectric film 27 adhering to the outer surface of the aluminum foil layer 26.

The bottom face 32 of the stylus body 31 made of diamond of the stylus 15 has a part of maximum width, which is greater than the track pitch of the disc 21, and an electrode part 33 having a thickness of 500 - 3000 A is formed by ion-implantation at rear face of the stylus at the rear edge of the bottom face 32. As the disc 21 rotates in the arrow direction, the tracing stylus 15 traces relatively along the surface of the disc 21, the electrostatic capacitance between the electrode part 33 and an aluminum foil layer 26 as of an electroconductive layer covering the entire surface of the disc varies in response to the pits 22, whereby the main information signal recorded by the pits 22 is reproduced.

At the same time, the pilot signals recorded by the pits 23 and 24 are also reproduced by the electrode part 33. In the case where the center of the electrode part 33 deviates from the centerline of the track, a level difference occurs in the reproduced pilot signals. A control signal formed in response to the level difference in supplied to the actuator part of the pickup device, whereby tracking servo operation is, carried out.

Next, the electrode part 33 constituting an essential part of the reproducing stylus of the present invention will now be described.

As the material for the stylus body 31, sapphire is used for producing a low-price reproducing stylus, but the use of a diamond, which has a great hardness, is desirable for long serviceable life of the stylus. As for the kind of diamond to be used, there are not specific particulars.

At the time of forming of the electrode part 33, the stylus body of prismatic shape of its state prior to grinding into a specific stylus shape is placed, in a state wherein it is supported by a supporting tool, in the sample chamber of an ion-implantation appar atus, which may be of any suitable known type. In one desirable embodiment of ion-implantation, hafnium (Hf) ions are implanted into a specific surface of a diamond stylus body with an ion acceleration voltage of the order of 30 to 100 KeV. By this process, the hafnium atoms are driven into the interstices between the carbon atom lattices of the diamond crystal, and the electrical resistance of the ionimplanted part is reduced to an extent whereby the part can be used as an electrode.The depth (i.e., thickness) of the ion-implanted layer thus obtained is, for example, 0.31lem, and the electric resistance of the part (electrode part) formed by this ionimplantation is approximately 1 KQ/cm (an example of value measured by electric resistance measuring apparatus). The electric resistance of a diamond is, for example, 1016 Q/cm., while the electrode part which has been subjected to ion-implantation exhibits electroconductivity.

The ions thus implanted in order to impart electroconductivity to the diamond are not limited to those of hafnium, ions of semimetals, semiconductors, and metals such as aluminum (At), molybdenum (Mo), titanium (Ti),tantalum (Ta), chromium (Cr), nickel (Ni), copper (Cu), gold (Au), silver (Ag), and carbon (C) being also usable.

Furthermore, the depth of ion-implantation can be controlled by suitably adjusting the ion-implantation energy. While the optimum ion acceleration voltage varies depending on the kind of ion and the depth of implantation, a desirable value thereof is in the range of 20 to 300 KeV, for example, a value of the order of 100 KeV. The reason for this is that an ion acceleration voltage less than 20 KeV will result in an insufficient implantation depth, while an ion acceleration voltage exceeding 300 KeVwill give rise to destruction of the crystal lattice of the diamond.

The quantity of ions implanted is selected in a range of 1015 to 1025 ions/cm2., preferably at a value of the order of 1 x 1023 ions/cm2. The ion implantation depth is selected in a range of 0.01 to 0.5 um, preferably at a value of the order of 0.3 ism.

When the ion-implantation thickness, that is, the thickness of the electrode part 33 is insufficient, the ion-implanted layer fails to function as an electrode.

On the other hand, when this thickness is excessive, satisfactory signal reproduction cannot be carried out because of the relationship with the dimension of the pits 22 in the track longitudinal direction.

Accordingly, with consideration of these conditions, the thickness of the electrode part is selected at a value within above stated range.

The ion-implantation thickness, the ionimplantation quantity, and other quantities are so selected in accordance with the kind of ions that the electrical resistance of the electrode part will be a value within a range of 1 Q/cm to 104 Q/cm.

The stylus body which has been subjected to the above described ion-implanation process and thereby has had an electrode part formed by the ionimplantation on a specific surface thereof is then formed by grinding to a specified shape. By this machining, a reproducing stylus 15 as shown partially in Figure 2 having an electrode part 33 of a shape with a width over a certain distance upward from the extreme tip which is less than the transverse track width of a pit 22 is obtained. It is desirable that the two lateral edges of the electrode part 33 be parallel, but a diverging angle of the order of 3 to 8 degrees between the two lateral edges, arising from the need to facilitate the grinding process, is not detrimental in actual practice.

The process of grinding a reproducing stylus of a shape as shown in Figure 2 is described in detail in the specification of British Patent Application No.

47733/77, entitled "Stylus for reproducing information signals recorded on a recording medium" of which applicant is the same as of the present application.

In the reproducing stylus of the present invention, the electrode part is formed by ion-implantation into a diamond stylus body and is not formed into a layer on the stylus body surface by evaporation deposition, sputtering, or some other conventional method. For this reason, there is no possibility of the electrode part being peeled off from the stylus body even after a long time of tracing the disc 21.

Therefore, in the case where the opposite lateral edges of the electrode part 33 have a diverging angle, the life end of the stylus is reached only when the electrode part 33 is worn away together with the stylus body 31 and the electrode width at the tip of the stylus exceeds track width. In a known reproducing stylus of like kind, the electrode tends to be peeled off from the stylus body, whereby the life end thereof is reached in about 100 hours. In contrast, the serviceable life of the reproducing stylus of the present invention is very long, being of the order of 2,000 hours.

A further advantageous feature of the ionimplantation process, in comparison with the vacuum evaporation deposition and sputtering processes, as applied to the production of reproducing styluses of the instant character, is that a large number of stylus bodies can be processed in a relatively simple manner with accurate control of the thickness of the electrode part. Accordingly, reproducing styluses of constant product quality with little deviation can be produced at low cost.

In the above described embodiment of the invention, a specific surface of the prismatic blank for the stylus body is subjected to an ion-implantation process, and, thereafter, the blank is ground into the specified stylus shape, the electrode part 33 being left. Alternatively, however, ion-implantation may be carried out with respect to a specific surface of a stylus body which has been ground beforehand into a specific stylus shape. In this case, the stylus body is so orientated that the surface on which the electrode part 33 is to be formed is perpendicular to the direction of the ion beam. The opposite lateral flank surfaces of the surface on which the electrode part is formed is inclined relative to the direction of the ion beam, and the quantity of implantation differs greatly depending on the implantation angle. For this reason, there is almost no ion-implantation into these flank surfaces, and even if there lissom ion-implantation, it will not be sufficient to form an ion-implantation thickness which will function as an electrode. Accordingly, as an effective result, the electrode part 33 is formed on substantially only the surface shown in Figure 2.

In the above described ion-implantation process, when the ion-implantation operation is continued further after ion-implantation has been carried out to a depth determined by factors such as the kind of ions and the ion acceleration voltage, atoms of the - ions adhere to and precipitate on the ion-implanted surface of the stylus body. In this case, the part where the atoms have adhered and precipitated on the surface is also effective as an electrode, and the above mentioned ion-implantation thickness is inclusive of the ion-implantation thickness and the thickness of this adhering and precipitated part.

In the ion-implatation process, furthermore, the control of the ion acceleration voltage is not limited to regulating this voltage at a constant value but may be a variable control depending on the necessity. In this case, when the process is carried with the ion acceleration voltage at a low value, ion atoms adhere to and are precipitated on the ion-implanted surface similarly as in the above described case.

The disc 21 has, on the upper surface of the disc structure 25 made of a polyvinyl chloride resin in the example shown in Figure 2, the thin aluminum foil layer 26 to function as the other electrode for the purpose of creating an electrostatic capacitance between it and the electrode part 33 of the reproducing stylus 15, but this layer may alternatively be a layer formed from a synthetic resin into which an electroconductive material such as carbon powder has been admixed. In this case, the electroconductive material admixed in the disc itself functions as an electrode and, moreover, is covered to a suitable degree by the synthetic resin at the surface. For this reason the thin film 26 and the film 27 of the above described example are not necessary.

While, in the above described example, the disc 21 does not have a reproducing stylus guide groove, it may be provided with a groove for guiding the reproducing stylus. In this case, of course, the shape of the tip of the stylus is so formed that it will appropriately match the guide groove.

Furthermore, the main information signal recorded in the pits 22 of the disc 21 may be a television video signal, or it may be a PCM audio signal. Thus, the kind of signal to which the reproducing stylus of the invention is applied is not limited.

Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope of the invention.

Claims

1. A reproducing stylus for reproducing an information signal from a recording medium on which said information signal has been recorded as variations in geometrical configurations, said reproducing stylus comprising a reproducing stylus body and an electrode part formed on a specific surface of the reproducing stylus body and functioning to reproduce the information signal recorded on the recording medium as variations in electrostatic capacitance responsive to the variations in geometrical configurations, said electrode part comprising a part of the reproducing stylus body rendered electroconductive by carrying out an ion-implantation process over said specific surface to a specific depth from the outer surface.

2. A reproducing stylus as claimed in claim 1 in which said electrode part has been formed by ion-implantation with ions of a substance from the group consisting of metals, semimetals, and semiconductors to the reproducing stylus body.

3. A reproducing stylus as claimed in claim 2 in which the ions are ions selected from the group consisting of ions of hafnium, aluminum, molybdenum, titanium, tantalum, chromium, nickel, copper, gold, silver, and carbon.

4. A reproducing stylus as claimed in claim 1 in which the ion-implatation process has been carried out at an acceleration voltage of 20 to 300 KeV to implant ions into said surface of the stylus body.

5. A reproducing stylus as claimed in claim 1 in which ions have been implanted in a quantity of of 1015 to 1025 ions/cm2. in said surface by the ionimplantation process.

6. A reproducing stylus as claimed in claim 1 in which ions have been implanted to a depth of 0.01 to 0.5 um in said surface by the ion-implantation process.

7. A reproducing stylus as claimed in claim 1 in which the electrode part has electric resistance of a value within a range of 1 #/cm - 104 ##Sllcm.

8. A reproducing stylus as claimed in claim 1 in which said ions are hafnium ions, and have been implanted to a depth of approximately 0.3 cm into the stylus structure at said at least one surface by the ion-implantation process carried out at approximately 30-100 KeV.

9. A reproducing stylus as claimed in claim 1 in which an ion acceleration voltage used in the ion-implantation process is variably controlled.

10. A reproducing stylus for information signal recording mediums of electrostatic capacitance type substantially as described with reference to the accompanying drawings.