MXPA06010138A - Optical recording disc adapted to storing data using an ultra-violet laser source - Google Patents

Abstract

Optical record carrier (20) adapted to storing data using a recording/reading device. The recording/reading device comprises an ultra-violet laser source emitting electromagnetic radiation (29) having a wavelength X in the range of 230 nm to 270 nm. The recording/reading device further comprises an objective lens (21) for focussing the electromagnetic radiation (29) on the optical recording carrier. NA is the numerical aperture of the objective lens. The optical record carier comprises a spiral track (22), which has a track pitch TP between 0.55 * lambda/NA and 0.75 * lambda/NA.

Description

OPTICAL RECORDING DISC ADAPTED TO STORE DATA USING AN ULTRAVIOLET LASER SOURCE Field of the Invention The present invention relates to an optical recording carrier for storing data using a recording / reading device. The recording / reading device comprises an ultraviolet laser having a wavelength? on the scale from 230 nm to 270 uni. The recording device comprises a target lens for focusing the light beam on the optical recording disc. The objective lens has a predetermined numerical aperture NA. BACKGROUND OF THE INVENTION Optical data storage systems have undergone an evolutionary increase in data capacity. The optical storage systems and in particular optical discs are read by a monochromatic beam of light, which is focused by means of an objective lens on the disc. The data capacity of the optical disc is limited by the size of the focal point of the monochromatic light beam. The optical dot size is proportional to the wavelength of the laser light used (?) And the numerical aperture of the objective lens (NA): D oc? NA REF: 174258 The total data capacity of an optical disc is determined by the size of the optical point of the reading and / or recording system. By increasing the numerical aperture (NA) of the objective lens and reducing the laser wavelength (?) The total data capacity was increased from 650 Mbytes (CD, NA = 0.45,? = 780 nm) to 4.7 Gbytes (DVD, NA = 0.60,? = 650 nm), and even 25 Gbytes (BD, before DVR, NA = 0.85,? = 405 nm). The data density BD (Blue-ray Disc) was derived from the capacity of the DVD by means of optical scaling. The focused beam of light must be driven by a control mechanism, in such a way that the track is followed accurately during the reading or recording of data. The track is the area on the disk on which the information will be recorded. Commonly the track has a spiral shape.

The focal point of the light beam has to follow the track to read or record information about the disc. For this purpose, a spiral slot structure is provided on an optical disk. For slot-only recording, data is written on the plain of the slot or on the adjacent surface plain. In this text, it is indicated that the plain closest to the incident light beam is the plain over groove. The farthest plain of the incident light beam is called the groove plain. The data can also be written both on the slot floor and on the slot.

This recording scheme is called slot / over slot recording. Figure 13 schematically represents both slot and slot recording. The track is the place where the data is written, in the plain on slot or in slot (recording only slot), or both on the plain in slot as on slot (recording in slot / envelope • slot). The distance between two tracks is called the track step (TP). The error in tracking the track is the difference between the desired position and the actual position of the focal point of the light beam. The desired position of the focal point is in the center of the track. The optical parameter used to generate the track tracking error signal is commonly known as a push-pull signal. The recording / reading device has auxiliary detectors to generate a push-pull signal based on the structure of the slot to thus detect a spatial deviation of the focal point with respect to the track. The pull / push signal is used to control players who put the recording head and consequently the focal point on the track during the rotation of the disc. The groove structure is characterized by the groove depth d, the flank angle,, the groove width Ll and the duty cycle of the groove. The definitions are given in Figure 2. In the case of a slot alignment shown in Figure 2, the passage between two adjacent slots corresponds to the passage of the track. The depth of groove d is the depth of the groove. The working cycle of the slot is defined by the width of slot Ll divided by track pitch TP. The flank angle? determines the slope between a slot and an adjacent plain. In the current definition, slot refers to the part of the substrate that is first observed by the incident light beam (the plain), in slot refers to the part of the substrate that is further away from the incident light beam (the slot ). In addition, the shape of the groove also has a significant impact on local light absorption. For example, it is known from the surface / slot recording scheme in the initial phase of the Blu-ray Disc system (the DVR system) that the surface and groove flats exhibited different recording phenomena. In the surface / groove definition scheme, different differences between surface and groove heating were observed with respect to writing power and thermal cross-writing (the phenomenon in which marks on adjacent tracks are partially erased by writing marks in the center court). Slot heating (in slot) leads to higher write powers and more thermal cross-writing. Proper selection of the shape of the slot with optimum performance both with respect to track tracking and optical absorption is therefore of paramount importance for the recording of high-quality optical data. Brief Description of the Invention The objective of the present invention is to provide an optical recording carrier for storing data, which has a scaled data capacity for deep UV recording and is optimized with respect to track tracking and optical absorption. The objective is solved by an optical recording carrier for storing data characterized by a spiral track having a track pitch TP of between 0. 55 *? / NA and 0.75 *? /? A for both single slot and slot / over slot recording,? It is the wavelength of the ultraviolet laser used to read / write data, and varies between 230 nm to 270 nm. ? A is the numerical aperture of the objective lens used to focus the light beam on the optical recording disk. A typical numerical aperture for high-end objective lenses, such as those currently used for the Blu-ray Disc system, is? A = 0.85. In that case, the effective point radius RO, that is, the radius at which the intensity of the laser point has decreased to 1 / e of its maximum intensity, of a system with? = 266nm is R0 = 99nm. This value of RO is compared with that of the other three known systems (CD, DVD and BD) in Table 1. Also, the related point area and the anticipated data capabilities are shown. If the effective point area (pRO2) is considered, it can be seen that a data capacity of 60-65 Gbytes is anticipated for the UV system. The data capacity gained is lower for a numerical aperture NA = 0.65 than for a numerical aperture NA = 0.85. Table 1 Point size and scaled data capabilities of four In conclusion, the effective point radius R0 is approximately 100 nm for? = 266 nm and NA = 0.85. If a track pitch is too small, the optical point will overlap widely with adjacent tracks and with written data which can lead to data deterioration, optical crosstalk during data reading and severe reduction. of track tracking signal by push-pull. On the other hand, if a track is searched for too large, the desired data capacity will never be obtained. The present invention achieves an optimal data track pitch with respect to minimal thermal cross-writing, acceptable optical crosstalk, acceptable push-pull signals and maximum achievable data capacity. Numerous simulations of cross-track (side) temperature profiles for a CD, DVD, BD and UV system are given in Figure 1. Figure 1 shows cross-track (side) temperature profiles for CD, DVD conditions , BD and UV as a result of laser pulse heating (50 ns write pulses). The profiles are normalized with the maximum temperature in the center of the track and plotted as a function of the cross-track coordinate (lateral) scale with the effective point size (RO). It is observed that all the temperature profiles are scaled to the same generic curve. From the figure, it is observed that the temperature in the center of the adjacent track has fallen to 0.2 times the maximum temperature Tmax in a radial position y = 2 * Ro. In rewritable optical discs based on phase change, the thermal cross-writing is in particular a (partial) recrystallization of marks on the adjacent tracks due to writing in the center track. Laser-induced recrystallization occurs at temperatures above the crystallization temperature (200 ° -300 ° C). The maximum temperature (Tmax) in the track is approximately 800 ° C-1000 ° C to make it possible to melt a sufficiently wide mark. Depending on the detailed properties of the recording material, a temperature of 0.2Tmax or less on an adjacent track is a reasonable criterion to avoid thermal crosswriting. In this case, the temperature remains below 200 ° C in the adjacent track. If we take TP = 2 * R0 as the minimum value of the track pitch, thermal crosswriting can be avoided. If a Gaussian profile is adjusted on the intensity distribution of the point, the following expression is obtained for RO: R0 = 0.52 * 1.22 *? / (2 * NA) To avoid thermal cross-writing as much as possible, TP = 2 * R0. Thus TP = 2 * R0 TP = 2 * 0.52 * 1.22 *? / (2 * NA) TP = 0.63 *? / NA A scale is secured around the value 0.63, particularly 0.55 *? / NA < TP < 0.75 *? / NA The lower limit of 0.55 is governed by thermal cross-writing in practical materials. The upper limit of 0.75 is related to the data capacity. Therefore, an optical disk for UV lasers is provided, which has an optimized track pitch. Preferably, the optical recording disk is characterized by a slot depth d where, where 1? 1 ? the slot depth is between - * - and - * -, nO being v 12 nO 4 «0 a refractive index of a cover layer of the optical recording disc. The groove depth determines the amplitude of the push-pull signal used for tracking the track. The push-pull signal must be strong enough to determine whether the laser spot is on the track or not. The groove depth is selected in such a way that a partial destructive interference occurs between a light beam of wavelength? reflected in slot and a wavelength of light? about slot. If the optical retardation between the reflected light beam from the surface and the reflected light beam from the slot is? / (N0 * 2), that is, 2 * d * n0 =? / 2, the two beams are canceled between yes completely and the total intensity of light reflected from the optical disc is minimal. nO is the refractive index of the medium between the recording head and the objective lens. In case a cover is used, the refractive index nO is that of the cover material, for incident recording with air n0 = l. d is the groove depth and 2 * d * n0 is the optical retardation between reflected beams from the groove and groove. The optical path difference between slot and groove is defined as d * n0 or half of the optical retardation. Thus, the groove depth must be smaller than d =? / (4 * n0), to avoid a complete destructive interference resulting in a very low reflected light intensity and consequently a very low signal amplitude. For groove depths greater than this value the polarity of the push-pull track tracking signal is reversed. Therefore, in practical disks, a path difference of about? / 8 is used. The minimum trajectory difference of? / 12 is to guarantee a sufficiently large track tracking signal. This is not a big limit since the amplitude of push-pull depends not only on the groove depth but also on the track pitch: for a larger track pitch, shallower slots can be accepted. The invention covers both slot-only recording and slot / over-slot recording. The only slot recording is the recording scheme in which only the plain in slot or over slot is used for recording. In slot / over-slot recording, both plains are used for recording. The two recording schemes are illustrated in Figure 13 for Blu-ray Disc conditions. The arrows indicate incident laser beams. A graph for slot / over-slot recording (upper graph) and a graph for single-slot recording (lower graph) are shown in figure 13. The lower graph represents a recording scheme, in which plains are used over slot for recording. The track passage TP of the lower graph is equal to 320 nm and corresponds to the distance between the centers of adjacent plains. The track pitch TP of the upper graph is equal to 300 nm and corresponds to the distance between the center of a plain and the center of an adjacent slot. The distance between the centers of two adjacent plains in the upper graph is equal to 600nm. Preferably, the optical disk has a DC slot duty cycle of between 30% and 70%. If the duty cycle reaches 0% or 100% the traction-push signal vanishes. BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. Figure 1 shows a diagram of cross track (side) temperature profiles for CD, DVD, BD and UV conditions as a result of laser pulse heating (50 ns write pulses). The profiles are normalized with the maximum temperature in the center of the track and plotted as a function of the cross-track (lateral) coordinates scaled with the effective optical spot size (R0). Figure 2 is a schematic representation of the preferred embodiment of the present invention. Figure 3 shows cross track temperature profiles in BD and UV slotted media. The temperature profiles in slot and on slot are shown. Figure 4 shows cross track temperature profiles for groove heating for various groove depths (UV recording conditions). Figure 5 shows cross track temperature profiles for heating on groove for two groove depths (UV recording conditions). Figure 6 shows a push-pull signal as a function of the radial position normalized to the track pitch. The recording is carried out through the cover layer. The track pitch TP is equal to 175 nm and the slot duty cycle is equal to 50%. Figure 7 shows a push-pull signal as a function of the radial position normalized to the track pitch. The recording is carried out through the cover layer, the track pitch TP is equal to 200 nm and the slot duty cycle equals 50%. Figure 8 shows a push-pull signal as a function of the radial position normalized to the track pitch. The recording is carried out through the cover layer, the track pitch TP is equal to 225 nm and the slot duty cycle is equal to 50%. Figure 9 shows a push-pull signal as a function of the radial position normalized to the track pitch. The incident recording with air is carried out. The track pitch TP is equal to 175 nm and the slot duty cycle is equal to 50%. Figure 10 shows a push-pull signal as a function of the radial position normalized to the track pitch. Incidental recording with air is carried out, the track pitch TP is equal to 200 nm and the slot duty cycle is equal to 50%. Figure 11 shows a push-pull signal as a function of the radial position normalized to the track pitch. Incidental recording with air is carried out, the track pitch TP is equal to 200 nm and the slot duty cycle is equal to 50%. Figure 12 shows two graphs representing cross track temperature profiles for groove and slot heating on optical discs having slot work cycles of 30%, 50% and 70%. Figure 13 is a schematic illustration of surface and groove and slot-only recording and heating. Detailed Description of the Invention Figure 2 is a schematic representation of one embodiment of the present invention. Shows the proposed conformational groove shape. The MIPI head (M refers to metal, I refers to the dielectric layers and P is the phase change layer) is deposited on a pre-grooved substrate. The optical recording carrier shown in Figure 2 consists of the following layers: a cover layer, an upper dielectric layer, the phase change layer PC, a lower dielectric layer, a metal layer and finally the substrate layer. The cone 29 indicates the direction of the focused incident electromagnetic radiation beam. In slot refers to the slot mastered on the substrate. A slot-only recording scheme is being considered. A slot / over slot recording scheme is a further embodiment of the present invention, which is not covered by the present embodiment. In the case of the slot alignment shown in FIG. 2, the passage between two adjacent slots corresponds to the track pitch TP. Other groove dimensions are flank width FW, width in groove Ll, width over groove L2, flank angle? and the groove depth d. In groove are the surface plains. As can be seen in figure 2, the track pitch TP of the recording medium is equal to 200 nm; the slot depth is equal to 20 nm; The slot duty cycle equals 50%. Both the width on groove and groove Ll and L2 have a width of 100 nm. The flank angle? is equal to 60 °. The flank width FW is equal to 11.5 nm. The following table 2 represents the properties of the optical disc of the present embodiment shown in Figure 2. N is the refractive index of the respective layer and K is the absorption coefficient of the layers other than the wavelength of 266 nm. Table 2 Head arrangement with layer thickness and optical properties (at wavelength = 266nm) The optical recording disc shown in Figure 2 is optimized for a laser having a wavelength equal to 266 nm and a target lens having a numerical aperture NA = 0.85. The track pitch equal to 200 nm is given by TP = 0.64 *? / NA. This is well within the scale covered by appended claim 1. The slot depth of 20 1,? nm corresponds to, which is within the scale 7.5 nO covered by claim 2. The 50% slot duty cycle is ponderable under appended claim 3. The cross track temperature profiles are given in Figure 3 for optical recording vehicles BD and UV with a groove depth of 20 nm. The other parameters for the BD head were TP = 320 nm, FW = 11.5 nm, L1 = L2 = 160 nm (DC = 50%), the parameters for the UV slot shape were TP = 200 nm, FW = 11.5 nm, L1 = L2 = 100 nm (DC = 50%). The UV medium corresponds to the mode of Figure 2. The temperature profiles for slot and slot heating are shown. The groove profiles are half of the offset TP to facilitate the comparison between groove heating and groove heating. For a 20 deep groove, it is observed that the differences between groove and groove heating are relatively small for BD recording conditions (NA = 0.85,? = 405 nm) while the differences are significant for UV recording (NA = 0.85,? = 266 nm). For both recording systems, heating over groove leads to lower side lobes and wider central peak temperatures. The two narrower curves shown in the graph of Figure 3 represent the UV temperature profiles for the groove and groove tracks. The temperature distribution of the UV curves is better than the distribution of the BD curves, since the UV curves have smaller side lobes and a higher peak. Therefore, thermal cross writing is more easily avoided. Thermal cross-writing is the phenomenon in which marks present on adjacent tracks are partially erased or overwritten during writing on the center track. Slot heating will cause higher temperatures in the adjacent tracks and therefore, slot recording is more sensitive to thermal crosswriting. In the case of the UV system, the marks on the adjacent tracks are located at y = TP = 200 nm. Therefore, the side lobes extend only up to y = 100 nm and most likely will hardly cause partial recrystallization of the adjacent marks. If the cast edge is taken as a criterion for the formation of marks, the slot recording results in a wider mark. Obviously, slot recording requires less writing power than slot recording. The cross track temperature profiles for groove heating are indicated in Figure 4 for various groove profanities. From the profiles, it is clear that a groove depth of 25 nm leads to a maximum temperature in the center of the track. The cross track temperature profiles for slot heating are shown in Figure 5. The temperature profiles are wider in the center track and also have less pronounced side lobes. Both slot and groove heating can be considered for UV recording. In the case of slot-only recording, the marks are written partially on the adjacent flanks and plains. If marks with a width exceeding the central plain are required, slot recording is beneficial. The relatively high side lobes can be used properly and only moderate energy levels are required to write the marks. If narrow marks are sought, for example to further reduce the passage of data tracks, slot recording is recommended. From a thermal point of view, the preferable slot depth is approximately 20-25 nm. further, the effect of the work cycle is important. The effect of the duty cycle is explained in Figure 12 for the Blue-ray Disc conditions. The upper graph in Figure 13 shows a temperature distribution for slot recording. The lower graph of Figure 13 shows a temperature distribution for slot recording. The track pitch TP, slot depth d and flank angle are identical for both graphs. The temperature profiles for different DC duty cycles, particularly 30%, 50% and 70% are shown in both graphs. The side lobes in the temperature distribution are made larger for slot recording as compared to recording over slot. A large duty cycle leads to wide temperature profiles. Confined temperature profiles result for small duty cycles. Traction-push track tracking signals are shown for different optical disc structures in Figures 6 to 11. The traction push signals in Figure 6 to 11 are calculation results. A track tracking signal for? = 266 nm and NA = 0.85 was assumed for the case of recording through a cover layer (refractive index n0 = 1.5) and for the case of incident recording with air (refractive index n0 = 1.0) for three different track steps (TP). Figure 6 shows a push-pull signal as a function of a radial position normalized to the track pitch. The recording is carried out through the cover layer. The track pitch TP is equal to 175 nm and the slot duty cycle is equal to 50%. In Figure 7 - the recording is carried out through the cover layer, the track pitch TP is equal to 200 nm and the slot duty cycle is equal to 50%. In FIG. 8 the recording is carried out through the cover layer, the track pitch is equal 225 nm and the slot duty cycle is equal to 50%. In FIG. 9, incident recording with air is carried out. The track pitch TP is equal to 175 nm and the slot duty cycle is equal to 50%. In FIG. 10, incident recording with air is carried out. The track pitch TP is equal to 200 nm and the slot duty cycle is equal to 50%. In FIG. 11, incident recording with air is carried out. The track pitch TP is equal to 200 nm and the slot duty cycle is equal to 50%. A further requirement that should be considered in the choice of slot geometry is the push-pull signal is required for the formation of tracks. Although a small track pitch is beneficial from the point of view of data capacity, it deteriorates the push-pull signal thus compromising the reliability of track tracking. In practice, a normalized push-pull signal of 0.2 provides an adequate compromise between reliability in track tracking and density of radial data. The curve for a 20 nm groove depth in the graph of Figure 7 is the curve for the optical disc of the preferred embodiment shown in Figure 2. The normalized push-pull signal exceeds 0.2 for the curve mentioned above. Therefore, the optical disc of the preferred embodiment provides a satisfactory push-pull signal. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims (3)

1. Having described the invention as above, the content of the following claims is claimed as property: 1. An optical recording carrier adapted to store data using a recording / reading device, the recording / reading device comprises a source of ultraviolet laser light which emit electromagnetic radiation that has a wavelength? on the 230 nm to 270 nm scale and an objective lens having a numerical aperture NA for focusing the electromagnetic radiation on the optical recording carrier, characterized in that it has a spiral track having a track pitch TP of between 0.55 *? / NA and 0.75 *? / A.
2. 2. The optical recording carrier according to claim 1, characterized by a groove depth d, wherein the groove depth is between - 1 * / 1 and _1_ * - / 1, nO being a refractive index of a layer of 12 «0 4 rcO cover of the optical recording carrier, or nO being equal to 1 in the case of an optical recording carrier without a cover layer. The optical recording carrier according to claim 1 or 2, characterized in that it has a slot duty cycle of between 30% and 70%.