Patent Application
20050122886
1. Field of the Invention
The present invention relates to a recording/reproducing head for recording and reproducing polarization information recorded on a dielectric substance, such as a ferroelectric recording medium, as well as a method of producing the recording/reproducing head, and a recording apparatus and a reproducing apparatus which use the recording/reproducing head.
2. Description of the Related Art
A technique of a recording/reproducing apparatus which uses SNDM (Scanning Nonlinear Dielectric Microscopy) for nano-scale analysis of a dielectric recording medium is suggested by the inventors of the present invention. In SNDM, it is possible to increase its resolution associated with the measurement to sub nanometer resolution, by using an electric conductive cantilever (or probe) with a small probe mounted on its tip, which is used for AFM (Atomic Force Microscopy) or the like. Recently, the development of a super high density recording/reproducing apparatus has been advanced, wherein the apparatus records data onto a recording medium having a recording layer made of a ferroelectric material, by using the technique of SNDM (refer to Japanese Patent Application Laying Open NO. 2003-0085969).
The recording/reproducing apparatus of this type which uses SNDM reproduces information by detecting a positive or negative direction of polarization of the recording medium. This is performed by using a change in an oscillation frequency of a LC oscillator, which includes (i) a high frequency feedback amplifier including an L component, (ii) a conductive probe mounted on this amplifier, and (iii) a capacitance Cs of the ferroelectric material under the probe, caused by a change ΔC in a small capacitance due to a non-linear dielectric constant which have origin in the distribution of the positive and negative of the polarization. Namely, it is performed by detecting the change in the distribution of the positive and negative of the polarization, as a change Δf in the oscillation frequency.
Moreover, by applying an alternating electric field whose frequency is sufficiently low with respect to the oscillation frequency in order to detect a difference in the positive and negative of the polarization, the oscillation frequency is changed along with the alternating electric field, and the rate of change in the oscillation frequency including its sign is determined by the non-linear dielectric constant of the ferroelectric material under the probe. Then, by FM (Frequency Modulation)-demodulating and extracting a component due to the alternating electric field, from a high-frequency signal of the LC oscillator which is FM-modulated in accordance with the change in the small capacitance ΔC along with the application of the alternating electric field, the record information (data) recorded on the ferroelectric recording medium is reproduced.
The record and reproduction of the record information is performed by using the probe as a recording/reproducing head. The probe can be broadly classified into a projection portion of a needle shape and a support portion for supporting the projection portion. By applying an electric field to between the projection portion and the recording medium, the information is recorded and reproduced as described above.
The projection portion can directly contact the recording medium. In particular, its tip portion is required to be needle-shaped or sphere-shaped, the size being several-tens nm or less, to practice the above-described recording and reproducing principle. There is, however, such a technical problem that it is difficult to form the needle-shaped member of several-tens nm or less in the conventional technique. For example, there is such a technical problem that even in trying to make the needle-shaped member of several-tens nm or less, the tip portion becomes flat or cannot be needle-shaped nor sphere-shaped. In such a case, the probe contacts a range of the dielectric recording medium which exceeds several-tens nm. Namely, such the contact as this between the surface of the probe and the dielectric recording medium may cause the application of an electric field to a range beyond a micro area or domain, which is one unit of a polarization condition as being an information unit. Because of this, there is such a technical problem that it is not possible to appropriately change the polarization condition and it is not impossible to detect the condition.
It is therefore an object of the present invention to provide a recording/reproducing head which has a relatively simple structure and whose tip portion can contact the dielectric recording medium on the order of several-tens nm or less, as well as a method of producing the recording/reproducing head relatively easily, and a recording apparatus and a reproducing apparatus which use the recording/reproducing head.
The above object of the present invention can be achieved by a recording/reproducing head for performing at least one of a record operation of recording information onto a dielectric recording medium and a reproduction operation of reproducing the information from the dielectric recording medium, the recording/reproducing head provided with: a support member which extends in a longitudinal direction (for example a longitudinal direction of the recording/reproducing head); and a projection portion which is mounted on the support member such that a tip of the projection portion faces the dielectric recording medium, the projection portion having a ridge-line on the tip, the projection portion being capable of contacting (including substantially contacting) the dielectric recording medium at one point on the ridge-line.
According to the recording/reproducing head of the present invention, the projection portion having a ridge-line on its tip can contact (or substantially contact) the dielectric recording medium at one point on the ridge-line. Therefore, it is possible to appropriately apply an electric filed in a domain (micro area) in which the polarization condition is recorded.
Specifically, the recording/reproducing head of the present invention is provided with the support member which extends in the longitudinal direction of the recording/reproducing head. It is preferable to use a material having electric conductivity as the support member, but as described later, it is possible to select an appropriate material in accordance with a resonance frequency of a resonance circuit (in other words, an oscillation frequency of an oscillator) in a reproducing apparatus. Alternatively, by selecting an appropriate material, it is also possible to change an vibration frequency obtained when the recording/reproducing head is moved along the surface of the information recording medium, as occasion demands. The projection portion is mounted on the support member such that the tip of the projection portion faces the dielectric recording medium. The projection portion may be mounted upright on the support member. The projection portion is also preferably constructed from a material having electric conductivity.
Particularly in the present invention, the projection portion has a ridge-line on the tip. The projection portion contacts or substantially contacts the dielectric recording medium at one point on the ridge-line. Incidentally, the “one point” here not only includes point contact as it is written, but also includes a range which can be regarded as the point contact in a recording apparatus and a reproducing apparatus as described later (e.g. a range with a diameter of approximately several tens nm). Namely, the tip of projection portion and the dielectric recording medium can contact on the order of several tens nm or less.
Normally, from the viewpoint of the application of an electric field to the domain, the projection portion is preferably formed such that it can contact the dielectric recording medium at one point (or in a range of approximately 10 nm order) on the tip portion. Specifically, the projection portion preferably has a shape such as a quadrangular pyramid. However, it is difficult to realize such a shape on the order of nanometer, and even if it realizes, it is not possible to produce it with stability and with a good yield. Therefore, the shape tends to be a pyramid with a ridge-line on the tip in many cases. It is conceivable to produce the projection portion that contacts the dielectric recording medium at one point, by mechanically cutting the tip of the project portion having the above shape (e.g. the pyramid shape with a ridge-line on the tip). But the mechanical cutting is difficult on the order of nanometer, and the production processes for the recording/reproducing head are difficult.
However, in the present invention, even in the case of the projection portion having such a shape (the pyramid shape with the ridge-line on the tip), the projection portion is formed to contact the dielectric recording medium at one point on the ridge-line in advance. For example, the ridge-line may be formed with an inclination with respect to the horizontal direction of the record/reproducing head (or the dielectric recording medium), or as described later, with an inclination with respect to the recording surface of the dielectric recording medium. By this, even without a shape such as a quadrangular pyramid, it is possible to contact the dielectric recording medium appropriately at one point on the ridge-line. Therefore, if the recoding/reproducing head of the present invention is used for a recording apparatus described later, there is such an advantage upon recording that it is possible to appropriately apply the electric field from the one point on the ridge-line, with respect to a domain whose polarization condition is desired to be changed, for example, without influence on the polarization conditions of adjacent domains. Moreover, if the recoding/reproducing head of the present invention is used for a reproducing apparatus described later, there is such an advantage upon reproducing that it is possible to appropriately apply an alternating electric field from the one point on the ridge-line, with respect to a domain whose polarization condition is desired to be detected, for example, without its reproduction signal influenced by the polarization conditions of adjacent domains. Therefore, it is possible to stabilize the record operation and the reproduction operation.
Consequently, according to the recording/reproducing head of the present invention, the tip thereof and the dielectric recording medium can contact on the order of several tens nm or less. By this, it is possible to appropriately record and reproducing the information.
Moreover, the support member and the projection portion may be formed in one body. Namely, even if the support member and the projection portion are formed from a single material, if the support member and the projection portion can be distinguished from a difference in their shapes, then, this aspect is included in the present invention.
In one aspect of the recording/reproducing head of the present invention, the ridge-line is inclined with respect to a recording surface of the dielectric recording medium.
According to this aspect, since the ridge-line is inclined with respect to the recording surface, it is possible to contact the dielectric recording medium (or the recording surface thereof) at one point on the ridge-line (i.e. on one end portion (point) of the ridgeline).
In this case, the ridge-line may be inclined or may not be inclined with respect to the support member. However, if the support member is placed along or in parallel with the recording surface of the dielectric recording medium, the ridge-line is preferably inclined even with respect to the support member. On the other hand, if the support member is not placed along or in parallel with the recording surface of the dielectric recording medium, the ridge-line may not be inclined even with respect to the support member.
In this aspect, the projection portion is provided with a crystal, and a crystal axis of the crystal is inclined with respect to a normal line of the recording surface of the dielectric recording medium and crosses the ridgeline at substantially right angles.
By constituting in this manner, in relation to the crystal axis that is inclined with respect to the normal line of the recording surface and that crosses the ridge-line at substantially right angles, it is possible to realize such a structure that the mechanical strength on the ridge-line of the inclined projection portion is extremely high. For example, if a crystal which has a not-inclined crystal axis with respect to the normal line of the recording surface and which has a ridge-line extending in a first direction is polished or the like to be a projection portion which has a ridge-line extending in a second direction different from the first direction, the projection portion possibly has low mechanical strength on the ridge-line in relation with the crystal axis.
In another aspect of the recording/reproducing head of the present invention, the ridge-line extends along the longitudinal direction.
According to this aspect, because of the ridge-line which is inclined along the longitudinal direction, the projection portion can contact the dielectric recording medium at one point on the ridge-line. Particularly if the recording/reproducing head of the present invention is used as a cantilever, it can contact the dielectric recording medium at one point on the ridge-line, regardless of the slight wobble (or the slight oscillation) of the support member which extends along the longitudinal direction. Even if the ridge-line does not extend along the longitudinal direction, for example, if it extends along a direction crossing the longitudinal direction, it is possible to receive the above-described various benefits from the viewpoint of the possibility of contact with the dielectric recording medium at one point.
In another aspect of the recording/reproducing head of the present invention, the projection portion is formed by using a mold which is formed by performing anisotropic etching with respect to an offcut substrate.
According to this aspect, by performing anisotropic etching with respect to the offcut substrate, as described later, it is possible to realize the shape of the projection portion which can contact the dielectric recording medium at one point on the ridge-line relatively easily. Therefore, the projection portion can contact the dielectric recoding medium at one point on the ridge-line.
The above object of the present invention can be also achieved by a production method of producing the above-described recording/reproducing head (including its various aspects), the production method provided with: a mold-forming process of forming a mold for forming the projection portion and the support member; and a member-forming process of forming the projection portion and the support member by using the formed mold, an offcut substrate being used as the mold in the mold-forming process.
According to the production method of the present invention, it is possible to produce the above-described recording/reproducing head of the present invention relatively easily.
Specifically, at first, in the mold-forming process, the mold for forming the recording/reproducing head is formed. Here, it is possible to form the mold by combining various processes, such as patterning by a resist and etching or the like. Particularly in the present invention, the offcut substrate whose crystal axis is inclined with respect to the surface of the substrate is used as the mold in the mold-forming process. The use of such an offcut substrate allows the formation of the mold in which the ridge-line is inclined in advance, when the mold portion for forming the projection portion is formed. Namely, it is possible to relatively easily form the mold for forming the projection portion which can contact the dielectric recording medium at one point on the ridge-line.
If the offcut substrate is not used, the mold is formed such that a portion of the ridge-line is parallel to the surface of the mold without an inclination, so that it is difficult to form the shape of the recording/reproducing head of the present invention. It is conceivable that the addition of machining by another process to this mold allows the formation of the mold for forming the shape in which the ridge-line is inclined, but this requires for fine machining (micro machining) on the order of nanometer, which is really difficult in reality and is expensive in cost. However, in the present invention, the fine machining on the order of nanometer is unnecessary by using the offcut substrate as the mold, and it is possible to form the mold for forming the shape of the projection portion of the recording/reproducing head of the present invention at low cost.
Then, in the member-forming process, the projection portion and the support member are formed. Here, they can be formed by using a film formation method (or a film growth method) or the like. Since the mold is formed in advance such that the ridge-line of the projection portion is inclined in the mold-forming process, it is possible to produce the above-described recoding/reproducing head of the present invention, relatively easily, without using a special method in the member-forming process.
Consequently, according to the production method of the present invention, it is possible to produce the above-described recoding/reproducing head of the present invention efficiently and relatively easily.
Incidentally, the production method of the present invention can take various aspects in association with the various aspects of the recording/reproducing head of the present invention.
In one aspect of the production method of the present invention, the mold for forming the projection portion is formed by performing anisotropic etching in the mold-forming process.
According to this aspect, in the case that a silicon substrate being the offcut substrate is used as the mold, by performing anisotropic etching with respect to the offcut substrate, the etching is performed with respect to a direction along the crystal axis (e.g. the normal direction of a (100) surface of the substrate), while the etching is relatively difficult to be performed in directions which are not along the crystal axis (e.g. the normal direction of a (111) surface of the substrate). Therefore, it is possible to relatively easily form the mold that the ridge-line of the projection portion is inclined, in accordance with the direction of the crystal axis (e.g. a direction of the offcut of the offcut substrate).
In an aspect of the production method of forming the mold by using the anisotropic etching as described above, the anisotropic etching may be performed by using a rectangular masking, in forming the mold for forming the projection portion in the mold-forming process.
By constituting in this manner, it is possible to produce the mold for forming such a shape that the ridge-line is inclined in accordance with the rectangular masking.
Normally, in order to produce the recording/reproducing head having the projection portion which can contact the dielectric recording medium at one point (e.g. the project portion having a quadrangular pyramid shape), it is necessary to make a square masking. However, it is difficult to form such a square masking that an error between the long side and the short side is approximately several-tens nanometer order, and it is expensive to do so. However, according to this aspect of the production method of the present invention, even if the masking is not square, but if it is rectangular, it is possible to produce the above-described recording/reproducing head of the present invention.
In another aspect of the production method of the present invention, at least the projection portion is formed by growing a crystal in a concave portion which is etched with an inclination in association with at least the projection portion in the mold in the member-forming process.
According to this aspect, in relation to the crystal axis of the crystal growing in the inclined concave portion, the projection portion constructed from the crystal whose growth is completed in the end has extremely high mechanical strength on the inclined ridge-line. For example, if a crystal is grown in a not-inclined concave portion and then it is polishing or the like, to thereby incline the ridge-line of the projection portion, the projection portion possibly has low mechanical strength on the ridge-line, in relation to the crystal axis.
The above object of the present invention can be also achieved by a recording apparatus for recording data onto a dielectric recording medium, the recording apparatus provided with: the above-described recording/reproducing head of the present invention (including its various aspects); and a record signal generating device for generating a record signal corresponding to the data.
According to the recording apparatus of the present invention, it is possible to record the data on the basis of the record signal generated by the recording signal generating device, while taking advantage of the above-described recording/reproducing head of the present invention. Namely, there is such an advantage upon the record operation that it is possible to appropriately apply an electric field from the one point on the ridge-line, with respect to a domain whose polarization condition is desired to be changed, for example, without influence on the polarization conditions of adjacent domains. If the projection portion can contact not at one point but on the entire ridge-line or in a broad range of the ridge-line, there is a possibility that even the polarization conditions of the adjacent domains may be changed. However, according to the recording apparatus of the present invention, it is possible to remove such a bad influence and stabilize the record operation.
The above object of the present invention can be also achieved by a reproducing apparatus for reproducing data recorded on a dielectric recording medium, the reproducing apparatus provided with: the above-described recording/reproducing head of the present invention (including its various aspects); an electric field applying device for applying an electric field to the dielectric recording medium; an oscillating device whose oscillation frequency (resonance frequency) varies depending on a difference in a capacitance corresponding to a non-linear dielectric constant of the dielectric recording medium; and a reproducing device for demodulating and reproducing an oscillation signal from the oscillating device.
According to the reproducing apparatus of the present invention, by applying an electric field to the dielectric recording medium by using the electric filed applying device, the oscillation frequency of the oscillating device is changed, due to a change in the capacitance corresponding to a change in the non-linear dielectric constant of the dielectric recording medium. Then, the oscillation signal corresponding to the change in the oscillation frequency of the oscillating device is demodulated and reproduced by the reproducing device, to thereby reproduce the data.
Particularly in the present invention, the data can be reproduced by taking advantage of the above-described recording/reproducing head of the present invention. Namely, there is such an advantage that it is possible to appropriately apply an alternating electric field from the one point on the ridge-line, with respect to a domain whose polarization condition is desired to be detected, for example, without its reproduction signal influenced by the polarization conditions of adjacent domains. If the projection portion can contact not at one point but on the entire ridge-line or in a broad range of the ridge-line, there is a possibility that the electric field is applied even with respect to the adjacent domains. Thus, there is the possibility that the change in the capacitance by the polarization conditions of the adjacent domains is detected, to thereby change the oscillation frequency which has the origin in the polarization condition of a domain which is originally desired to be reproduced. However, according to the reproducing apparatus of the present invention, it is possible to remove such a bad influence and stabilize the reproduction operation.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with reference to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below.
As explained above; according to the recording/reproducing head of the present invention, it is provided with the support member and the projection portion. Therefore, the tip thereof and the dielectric recording medium can contact (or substantially contact) on the order of several tens nm or less. By this, it is possible to appropriately record and reproduce the information.
Moreover, according to the production method of the present invention, it is provided with the mold-forming process and the member-forming process. Therefore, it is possible to produce the recording/reproducing head of the present relatively easily and efficiently.
Moreover, according to the recording apparatus of the present invention, it is provided with the recording/reproducing head and the record signal generating device. Therefore, it is possible to receive various benefits owned by the recording/reproducing head of the present invention, and thus, it is possible to record the data with more stability.
Furthermore, according to the reproducing apparatus of the present invention, it is provided with: the recording/reproducing head; the electric field applying device; the oscillating device; and the reproducing device. Therefore, it is possible to receive various benefits owned by the recording/reproducing head of the present invention, and thus, it is possible to reproduce the data with more stability.
The embodiment associated with the recording/reproducing head of the present invention will be hereinafter explained with reference to the drawings.
At first, with reference to
At first, the recording/reproducing head in the embodiment will be explained with reference to
As shown in
The projection portion 110 has a narrowed and pointed tip so that an electric field is applied to a dielectric recoding medium 20 as described later (refer to
Particularly in the embodiment, the portion which can actually contact (or substantially contact) the dielectric recording medium 20 out of the projection portion 110 (i.e. the tip portion of the projection portion 110) is a point (a contact point or a contact portion) 111 positioned at one end of a ridge-line 110L and is satisfied with the size of 10 nm order described above. Therefore, on a dielectric recording/reproducing apparatus 1 as described later (refer to
The support member 130 is a base for supporting the recording/reproducing head 100. The support member 130 has electric conductivity as with the projection portion 110. Moreover, as described later, the support member 130 and the projection portion 110 may be formed in one body (refer to
Furthermore, as described later, the projection portion 110 and the support member 130 constitute a part of a resonance circuit 14 in the reproduction operation as a part of a probe 11 (refer to
Even in a recording/reproducing head 101 as shown in
Moreover, even if the projection portion 110 is not formed at one of the end portions of the support member 130, as shown in
Now, a comparison example of the recording/reproducing head in the embodiment will be explained with reference to
In the recording/reproducing head which requires for a machining accuracy of nanometer order, it is difficult to realize an ideal shape such as a quadrangular pyramid (i.e. the shape to contact the dielectric recording medium 20 at the point), and in fact, in many cases, the recording/reproducing head has a shape like that of the recoding/reproducing head in the comparison example. In this case, the recording/reproducing head in the comparison example can contact the dielectric recording medium 20 on the whole ridge-line, as shown in
However, in the recording/reproducing head 100 (or 101 or 102) in the embodiment, the projection portion 110 is inclined from the normal line of the recording surface, i.e., the ridge-line 110L is inclined from the recording surface, so that the recoding/reproducing head 100 (or 101 or 102) can contact the dielectric recording medium 20 at the point 111. Therefore, it is possible to appropriately apply an electric field in a single domain, and as a result, it is possible to record and reproduce the information appropriately.
Moreover, even in the recording/reproducing head as shown in
(ii) PRODUCTION METHOD FOR RECORDING/REPRODUCING HEAD
Next, with reference to
Incidentally, the recording/reproducing head produced in the production method explained here has the projection portion 110 and the support member 130 which are unified. However, even if the projection portion 110 and the support member 130 are not unified, the recording/reproducing head can be produced in the same production method, and it is obvious that such a production method is also included in the scope of the present invention.
At first, as shown in
Particularly in the embodiment, as the silicon substrate 201, a silicon offcut substrate is used. The silicon offcut substrate is a silicon substrate which is cut not along its (100) surface but at a predetermined angle with respect to the (100) surface, in cutting the substrate from a silicon wafer, for example. Namely, it is a silicon substrate whose crystal axis (i.e. the normal line of the (100) surface) is inclined at a predetermined angle with respect to the cut surface of the silicon substrate 201. Incidentally, an arrow shown in
Then, as shown in
Then, as shown in
Incidentally,
Then, as shown in
After the etching of the silicon dioxide film 202, the photoresist 203 is removed. Here, the removal of the photoresist 203 may be performed by dry etching or wet etching.
Then, as shown in
Here, the silicon substrate 201 has such a characteristic that the etching can be performed in the normal direction of the (100) surface (i.e. the offcut direction in
Incidentally,
Incidentally, the recording/reproducing head associated with the above-described comparison example is generally produced by using a silicon substrate whose crystal axis is not inclined as a mold. Therefore, as with the recoding/reproducing head in the embodiment, in order to form the projection portion 110 which can contact the dielectric recording medium 20 at the point 111 (i.e. in order to form the projection portion 110 such as a quadrangular pyramid), it is necessary to apply the photoresist 203 such that the window of the photoresist 203 is square. The window of the photoresist 203 is preferably square, with an error between the long side and the short side of approximately several-tens nanometer order. However, it is difficult to form such a square accurately, under the condition of the nanometer order.
In the embodiment, the crystal axis is inclined, so that even if the photoresist 203 is not square but rectangular, for example, it is possible to produce the recording/reproducing head which can contact the dielectric recording medium 20 at the point 111 (i.e. at one point on the inclined ridge-line 110L). Therefore, without considering a fine mask on the order of nanometer, it is possible to produce the recording/reproducing head which can contact the dielectric recording medium 20 at the point 111, relatively easily and at low cost, which is extremely advantageous.
Then, as shown in
Incidentally,
Then, as shown in
Incidentally,
Then, as shown in
Then, as shown in
Moreover, the diamond film is used as the above-described projection portion 110, so that it needs to have electric conductivity. Therefore, B (Boron) is doped in the diamond film by adding a doping gas, such as B2H6 (diborane) and (CH3O)3B (trimethoxy boron).
Incidentally, the method of growing the diamond film is not limited to the one by the scratch process as shown in
Then, as shown in
Then, as shown in
Incidentally, in this case, the support member 130 and the projection portion 110 are formed in one body, so that in the explanation below, the projection portion 110 shall include a function as the support member 130.
Then, after the projection portion 110 is formed, etching is performed, as shown in
Then, as shown in
Incidentally,
Incidentally, with respect to the specific size of the recording/reproducing head shown in
In this case, the support member 130 is unified with a support base 130a. The support base 130a is fixed, and the support member 130 is unified with the support base 130a such that the support member 130 can move (or wobble or oscillate) slightly as a cantilever in accordance with its elasticity. Even in this case, the support member 130 and the support base 130a may be collectively referred to as the support member 130.
Then, as shown in
Moreover, the groove-cutting machining is performed to the glass 206, by forming a cut in the vicinity of the center of the glass 206. This is formed to easily break the glass 206 in a process described later (refer to
Incidentally,
Then, as shown in
Then, as shown in
Then, with reference to
As with the recording/reproducing head 102 in one modified example shown in
Moreover, as with a recording/reproducing head 103 in another modified example shown in
Next, the recoding/reproducing apparatus which uses the recording/reproducing head in the embodiment described above will be explained.
(i) Basic Structure
At first, the basic structure of the dielectric recording/reproducing apparatus in the embodiment will be explained with reference to
The dielectric recording/reproducing apparatus 1 is provided with: the probe 11 for applying an electric field with its tip portion facing a dielectric material 17 of the dielectric recording medium 20; a return electrode 12 for returning the high-frequency electric field for reproduction applied from the probe 11; an inductor L placed between the probe 11 and the return electrode 12; an oscillator 13 which oscillates at a resonance frequency determined from the inductor L and a capacitance Cs in a portion formed in the dielectric material 17 under the probe 11 and polarized correspondingly to the record information; an alternating current (AC) signal generator 21 for applying an alternating electric field which is intended to detect the polarization condition recorded in the dielectric material 17; a record signal generator 22 for recording the polarization condition into the dielectric material 17; a switch 23 for switching outputs from the AC signal generator 21 and the record signal generator 22; a High Pass Filter (HPF) 24; a demodulator 30 for demodulating a FM signal modulated by the capacitance Cs corresponding to the polarization condition owned by the dielectric material 17 under the probe 11; a signal detector 34 for detecting data from the demodulated signal; and a tracking error detector 35 for detecting a tracking error signal from the demodulated signal.
The probe 11 is connected to the oscillator 13 via the HPF 24, and connected to the AC signal generator 21 and the record signal generator 22 via the HPF 24 and the switch 23. Incidentally, with respect to the probe 11, for example, a cantilever shape or a needle shape, as in
Particularly in the embodiment, as the probe 11, the recording/reproducing head 100 in the embodiment described above is used. Namely, the recording/reproducing head which can contact the dielectric recording medium 20 at the point 111 is used.
Incidentally, it is also possible that a plurality of probes 11 are provided. In this case, a plurality of AC signal generators 21 are preferably provided for the respective probes 11. Moreover, in order to distinguish, on the signal detector (detectors) 34, reproduction signals corresponding to each of a plurality of the AC signal generators 21, it is preferable that a plurality of signal detectors 34 are provided and that each of the signal detectors 34 obtains reference signal from the corresponding AC signal generator 21, to thereby output the corresponding reproduction signal.
The return electrode 12 is an electrode for returning the high-frequency electric field applied to the dielectric material 17 from the probe 11 (i.e. a resonance electric field from the oscillator 13), and is placed to surround the probe 11. Incidentally, the shape and placement of the return electrode 12 can be arbitrarily set as long as the high-frequency electric field can return to the return electrode 12.
The inductor L is placed between the probe 11 and the return electrode 12, and may be formed using a micro-strip-line, for example. The inductor L and the capacitance Cs constitute the resonance circuit 14. The inductance of the inductor L is determined such that this resonance frequency is approximately 1 GHz, for example.
The oscillator 13 is an oscillator which oscillates at the resonance frequency determined from the inductor L and the capacitance Cs. The resonance frequency varies, depending on the change of the capacitance Cs. Therefore, FM modulation is performed correspondingly to the change of the capacitance Cs determined by the polarization domain corresponding to the recorded data. By demodulating this FM modulation signal, it is possible to read the data recorded in the dielectric recording medium 20.
Incidentally, as described in detail later, the probe 11, the return electrode 12, the oscillator 13, the inductor L, the HPF 24, and the capacitance Cs in the dielectric material 17 constitute the resonance circuit 14. The FM signal amplified on the oscillator 13 is outputted to the demodulator 30.
The AC signal generator 21 applies an alternating electric field to between the return electrode 12 and an electrode 16. The frequency of the alternating electric field is approximately 5 kHz, and the alternating electric field is applied to the domain of the dielectric material 17. In the dielectric recording/reproducing apparatus having the plurality of proves 11, the frequencies of the alternating electric fields are used as reference signals in the signal detector (detectors) 34 to distinguish reproduction signals detected with the probes 11.
The record signal generator 22 generates a signal for recording (hereinafter referred to as a “record signal”), which is supplied to the probe 11 at the time of recording. This record signal is not limited to a digital signal but may be an analog signal. This record signal includes various signals, such as audio data, video data, and digital data for a computer. An AC signal which is superimposed to the record signal is used, as a reference signal in the reproduction operation, to distinguish and reproduce the reproduction signal of each probe 11.
The switch 23 selects its output to supply an AC signal (the alternating electric field) from the AC signal generator 21 at the time of reproducing, or a record signal from the record signal generator 22 at the time of recording, to the probe 11. A mechanical relay or a semiconductor circuit may be used for this device. In the case of the analog signal, the relay is preferably provided, and in the case of the digital signal, the semiconductor circuit is preferably provided.
The HPF 24 includes an inductor and a condenser. The HPF 24 is used to constitute a high pass filter for cutting off a signal system to prevent the signals obtained from the AC signal generator 21 and the record signal generator 22 from interfering with the oscillation of the oscillator 13. The cut-off frequency is f=1/{2π{square root}{square root over ( )}(LC)}, wherein L is the inductance of the inductor included in the HPF 24, and C is the capacitance of the condenser included in the HPF 24. The frequency of the AC signal is approximately 5 KHz, and the resonance frequency of the oscillator 13 is approximately 1 GHz, so that the separation at a first LC filter can be performed sufficiently. A higher-order filter may be used, but since the number of elements increases, the size of the apparatus may be increased.
The demodulator 30 demodulates the resonance frequency of the oscillator 13, which is FM-modulated due to the small change of the capacitance Cs, and reconstructs a waveform corresponding to the polarized condition of a portion which is traced by the prove 11. If the recorded data are digital data of “0” and “1”, there are two types of frequencies which are modulated, and the data is reproduced easily by distinguishing the frequencies.
The signal detector 34 reproduces the recorded data from the signal demodulated on the demodulator 30. A lock-in amplifier is used as the signal detector 34, for example, and synchronized detection is performed on the basis of the frequency of the alternating electric field of the AC signal generator 21, to thereby reproduce the data. Incidentally, it is obvious that other phase detection devices may be used.
The tracking error detector 35 detects a tracking error signal for controlling the apparatus (especially, tracking operation), from the signal demodulated on the demodulator 30. The detected tracking error signal is inputted into a tracking mechanism for the control.
Next, one example of the dielectric recording medium 20 shown in
As shown in
The record area 8 is an area to record the data therein and has tracks and spaces between the tracks. Moreover, on the tracks and the spaces, such areas are provided that record therein control information associated with the record and reproduction. Furthermore, the inner area 7 and the outer area 9 are used to recognize the inner position and the outer position of the dielectric recording medium 20, respectively, and can be used as areas to record therein information about the data which is recorded, such as a title, its address, a recording time length, and a recording capacity. Incidentally, the above-described construction is one example of the dielectric recording medium 20, and other construction, such as a card-shape, can be also adopted.
Moreover, as shown in
The substrate 15 is Si (silicon), for example, which is a preferable material in its strength, chemical stability, workability, or the like. The electrode 16 is intended to apply an electric field between the electrode 16 and the probe 11 (or the return electrode 12). By applying such an electric field to the dielectric material 17 that is greater than the coercive electric field of the dielectric material 17, the polarization direction is determined. By determining the polarization direction in accordance with the data, the record operation is performed.
The dielectric material 17 is formed by using a known technique, such as spattering method of LiTaO3 or the like, which is a ferroelectric substance, onto the electrode 16. The record operation is performed with respect to such a Z surface of LiTaO3 that the plus and minus surfaces of the polarization have a 180-degree domain relationship. It is obvious that other dielectric materials may be used. The dielectric material 17 forms the small polarization at high speed by using a direct current bias voltage and a voltage for the data which are both applied at the same time.
Alternatively, as the shape of the dielectric recoding medium 20, for example, there are a disc shape and a card shape and the like. The displacement of the relative position with the probe 11 is performed by the rotation of the dielectric recording medium 20, or by displacing linearly either the probe 11 or the dielectric recording medium 20.
(ii) Operation Principle
Next, with reference to
(Record Operation)
At first, with reference to
As shown in
For example, it is assumed that the domains have a downward polarization P when an electric field is applied from the probe 11 to the electrode 16, and that the domains have an upward polarization P when an electric field is applied from the electrode 16 to the probe 11. This corresponds to a condition where the information is recorded. If the probe 11 is moved in a direction shown with the arrow, a detection voltage is outputted as a rectangular wave having a high level or a low level (i.e. the digital signal), correspondingly to the polarization P. Incidentally, this level varies depending on the extent of the polarization P, to thereby allow the recording as the analog signal.
Particularly in the embodiment, the use of the recording/reproducing head 100 as the probe 11 allows the contact (substantially contact) with the dielectric recording medium 20 at the point 111. Therefore, it is possible to apply an electric field with pinpoint precision with respect to a domain whose polarization direction is originally desired to be changed. If the recording/reproducing head in the comparison example shown in
(Reproduction Operation)
Next, with reference to
The non-linear dielectric constant of a dielectric substance changes correspondingly to the polarization direction of the dielectric substance. The non-linear dielectric constant of the dielectric substance can be detected as a difference in the capacitance of the dielectric substance or a difference in the change of the capacitance, when an electric field is applied to the dielectric substance. Therefore, by applying an electric field to a dielectric material and detecting, at that time, a difference in the capacitance Cs or a difference in the change of the capacitance Cs in a certain domain of the dielectric material, it is possible to read and reproduce the data recorded as the polarization direction of the dielectric material.
Specifically, at first, as shown in
Then, the probe 11 is approached to the recording surface until the distance between the tip of the probe 11 and the recording surface becomes extremely small on the order of nanometers. Under this condition, the oscillator 13 is driven. Incidentally, in order to detect the capacitance Cs of the dielectric material 17 under the probe 11 highly accurately, it is preferable to contact the probe 11 with the surface of the dielectric material 17, i.e. the recording surface. However, in order to read the data recorded in the dielectric material 17 at high speed, it is necessary to relatively displace the probe 11 on the dielectric recording medium 20 at high speed. Thus, in view of reliability in the high-speed displacement, and the prevention of damage caused by the collision and friction between the probe 11 and the dielectric recording medium 20, or the like, it is practically better to make the probe 11 approach the recording surface close enough to regard this as the actual contact (i.e. substantially contact), than make the probe 11 contact the recording surface. Particularly in the embodiment, it is the point 111 out of the probe 11 that contacts the recording surface.
Then, the oscillator 13 oscillates at the resonance frequency of the resonance circuit, which includes the inductor L and the capacitance Cs associated with the dielectric material 17 under the probe 11 as the constituent factors. The central frequency of the resonance frequency is set to approximately 1 GHz, as described above.
Here, the return electrode 12 and the probe 11 constitute a part of the resonance circuit 14 including the oscillator 13. The high-frequency signal of approximately 1 GHz, which is applied to the dielectric material 17 from the probe 11, passes through the dielectric material 17 and returns to the return electrode 12, as shown with solid lines in
In addition, the change of the capacitance Cs corresponding to the non-linear dielectric constant of the dielectric material 17 is extremely small, and in order to detect this change, it is necessary to adopt a detection method having high detection accuracy. In a detection method using FM modulation, generally, it is possible to achieve the high detection accuracy, but it is necessary to further improve the detection accuracy to likely detect the small capacitance change corresponding to the non-linear dielectric constant of the dielectric material 17. Thus, in the dielectric recording/reproducing apparatus 1 in the embodiment (i.e. a recording/reproducing apparatus which uses the SNDM principle), the return electrode 12 is placed in the vicinity of the probe 11 to shorten the feedback route (the feedback path) to the resonance circuit 14 as much as possible. By this, it is possible to obtain extremely high detection accuracy, and thus it is possible to detect the small capacitance change corresponding to the non-linear dielectric constant of the dielectric substance.
After the oscillator 13 is driven, the probe 11 is displaced in parallel with the recording surface on the dielectric recording medium 20. By the displacement, the domain of the dielectric material 17 under the probe 11 is changed, and whenever its polarization direction changes, the capacitance Cs changes. If the capacitance Cs changes, the resonance frequency (the oscillation frequency) of the oscillator 13 changes. As a result, the oscillator 13 outputs a signal which is FM-modulated on the basis of the change of the capacitance Cs.
This FM signal is frequency-voltage converted by the demodulator 30. As a result, the change of the capacitance Cs is converted to the change of a voltage. The change of the capacitance Cs corresponds to the non-linear dielectric constant of the dielectric material 17. The non-linear dielectric constant corresponds to the polarization direction of the dielectric material 17. The polarization direction corresponds to the data recorded in the dielectric material 17. Therefore, a signal obtained from the demodulator 30 is a signal whose voltage changes correspondingly to the data recorded in the dielectric recording medium 20. Moreover, the signal obtained from the demodulator 30 is supplied to the signal detector 34, and the data recorded in the dielectric recording medium 20 is extracted by the synchronized detection, for example.
At this time, in the signal detector 34, the AC signal generated by the AC signal generator 21 is used as a reference signal. This makes it possible to extract the data highly accurately by referring the reference signal (i.e. synchronizing with the reference signal), as described above, even if the signal obtained from the demodulator 30 includes much noise or the data to be extracted is weak, for example.
Particularly, in the embodiment, the use of the recording/reproducing head 100 as the probe 11 allows the contact (substantially contact) with the dielectric recording medium 20 at the point 111. Therefore, it is possible to apply an alternating electric field with pinpoint precision with respect to a domain whose polarization direction is originally desired to be detected. If the recording/reproducing head in the comparison example shown in
Moreover, in the above-described embodiment, the dielectric material 17 is used for a recording layer, but from the viewpoint of the presence or absence of spontaneous polarization and the non-linear dielectric constant, the dielectric material 17 is preferably a ferroelectric substance.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
The entire disclosure of Japanese Patent Application No. 2003-392773 filed on Nov. 21, 2003 including the specification, claims, drawings and summary is incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-392773 | Nov 2003 | JP | national |
