JP2002503801A - Method and apparatus for determining flying height of recording head - Google Patents

Abstract

(57) [Summary] The present invention features a flying height measurement system that measures the flying height of a slider (104) above a disk (112). The flying height measurement system includes a light source (100), a slider (104), a detector module (106), and a processor (108). The light source (100) generates light along one optical path. The slider (104) includes the objective lens arranged so that light from the light source impinges on the objective lens (124) and is directed to the surface (110) of the disk (112). Light propagating from the disk (112) is directed to the detector (106). The processor (108) estimates the flying height of the slider (104) based on the output of the detector module.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION The present invention relates to a disk storage system of the type used to store information. In particular, the invention relates to an apparatus for determining fly height in a head / gimbal assembly of such a disk storage system.

[0002] Disk storage systems are known in the art and are used to store information for later retrieval. Such disk storage systems include rotating disks that carry information. When the disc rotates at high speed, the transducing head (or
In some cases, the read-back head is located above the surface of the disk.
The head is carried on a slider that is designed to "fly" just above the spinning disk. The head can then also be used to write information from the disc. Such information may be, for example, magnetically or optically encoded on the disk surface.

[0003] Increasing storage density is becoming increasingly important. One well-known method for increasing storage density is to reduce the "flying height" of the head. Fly height is defined as the distance between the disk surface and the head or slider during operation of the storage system. Reducing the flying height allows information to be written or read back more accurately and allows such information to be stored in a smaller area (ie, more densely).

[0004] Various techniques have been used in the art to measure head flying height. For example, if a disk is designed to operate at a certain flying height, this flying height must typically be measured to ensure that the system operates within this specification. Generally, this flying height is measured before assembling the head and slider assembly into a disk drive. One method of measuring flying height is
By measuring the electrical capacitance between the head and the disk. Another common technique for measuring fly height employs the method of an optical interferometer, which uses a transparent test disk to fly the slider. Light from the light source onto the other side of the disk is illuminated through the disk onto the slider. Using known techniques, the reflected light can be inspected to determine fly height. US Patent No. 5,280
No. 340, issued Jan. 18, 1994, Lacey describes many such techniques for measuring fly height.

[0005] Another technique used to measure and characterize the head is to measure the read-back signal provided by the head during operation. The signal can be tested for a number of different parameters, including signal strength, inter-signal interference, off-track sensitivity, and the like. For example, U.S. Pat. No. 5,068,754, Jan. 1991
Published January 26, one method and apparatus for measuring bit shifts in magnetic disk drives is described.

[0006] Optical discs provide an alternative to recording media that is purely magnetic. Optical disk drives can be used to obtain high storage densities. One way to increase storage density involves using near-field recording to reduce spot size. Near-field recording involves an optical component mounted on a slider that is approximately within a distance of the order of the wavelength of the disk surface or less. Then, the energy transmitted through the optics element is evanescent (evanescent).
transferred to the surface of the disc through the bond. Solid immersion lens (S
IL) or the like can be used with an objective lens to produce a minimal spot.

Generally, in optical storage systems, data is in the form of marks carried on the surface of the disk, which marks are detected using reflected light of a laser. A number of different optical disc technologies are known in the art. For example, compact discs are currently used to record digital data such as computer programs and digitized music. Typically, compact discs are permanently recorded during manufacture. Another type of optical system is the write-once (WORM) system, which allows a user to write information to a blank disc. Other types of systems are erasable, such as phase change systems and magneto-optical (MO) systems. Phase change systems detect data by sensing changes in reflectivity. The MO system reads the data by measuring the rotation of the polarization of the incident light by the storage medium.

SUMMARY OF THE INVENTION The present invention features a measurement system for estimating the flying height of a recording head relative to a rotating disk. Some attributes of the light reflected from the rotating disk depend on the distance of the recording head to the rotating disk. This flying height measurement system
Includes power supply, slider, detector module, and processor. The objective lens included in the slider is arranged such that light from the light source hits it and is directed to the surface of the disk.

In a first configuration, a detector module receives light reflected from a disk.
A processor estimates the flying height of the slider based on the output of the detector module. In an alternative arrangement, the light transmitted through the disc is received by a detector module. The transmitted light is not spatially dispersed based on wavelength. again,
A processor estimates the flying height of the slider based on the output of the detector module.

In another aspect, the invention features a method of determining a flying height of a slider with respect to a rotating disk, comprising: a) directing light to an objective lens disposed on the slider; and b) propagating light. Measuring the attributes of the light propagating from the disk with a detector module arranged to receive the light, wherein the light directed to the detector is not spatially dispersed based on wavelength; c) the detector And estimating the flying height based on the output of.

A detector module performing this method may include one lens and one two-element detector, wherein the flying height assesses the difference between the signals from the two elements of the detector, It is estimated by comparing this difference with values from a standard curve. In another embodiment of the method, the detector module comprises one polarizing beam splitter;
And two photosensitive elements each configured to measure one component of the split beam. In another embodiment, the detector module includes a detector array, and the fly height is determined by the intensity distribution, phase distribution,
Alternatively, it is estimated by inspecting the polarization distribution.

Detailed Description of the Preferred Embodiment A slider with an objective lens can be used to obtain the distance from the slider to the rotating disk, ie, the flying height. Only one monochromatic or quasi-monochromatic light source is required. The processing between the slider and the disk is kept almost constant in order to make the measurement. Light propagating from the disk is directed to a detector. For example, light reflected back from the disc through the objective lens can be directed to the detector by a beam splitter. Alternatively, light transmitted through the disc can be directed to the detector.

[0013] The detector measures one or more attributes of the reflected (transmitted) light. Attributes suitable for obtaining a distance measurement include, for example, polarization, intensity distribution, and / or phase distribution. Correlating these attributes with the distance attributes allows the microprocessor to monitor the detector output using subsequent measurements to provide output regarding fly height.

Since the slider for an optical recording head is generally equipped with one objective lens and possibly other suitable optics, this solution for measuring the flying height is to reduce the flying height of the optical recording head. Particularly suitable for measuring. Nevertheless, other recording heads may include a slider equipped with the desired objective lens and other optical lenses to perform the distance measurement. Thus, the specifications of the magnetic disk drive system can be measured with the solution described herein.

Some particularly suitable optical recording heads include near-fi
eld) an optical recording head is included. A near-field optical recording head generally has a flying height on the order of the wavelength of light or less. The optical instrument mounted on the slider is coupled to the surface of the disc through evanescent coupling due to the small separation distance. Slider optics generally include an objective lens that focuses light on or slightly below the bottom surface of the slider. Slider optics on the near field recording head also include a solid immersion lens (SIL) or the like to reduce spot size.

Referring to FIG. 1A, a measurement system for measuring light reflected from a disk includes a light source 100, a beam splitter 102, a slider 104, a detector module 106, and a processor 108. When the disk 112 is in a predetermined position,
The measurement system is located near the surface 110 of the disk 112 with respect to the disk rotation system with the slider 104. The disk rotation system includes a motor 114 such as a spindle motor that rotates a disk 112. The measurement system optionally includes a light source 10 reflected by the beam splitter 102.
A power meter 116 may be included that is arranged to receive a portion of the incident light from zero.

In an alternative embodiment, shown in FIG. 1B, the measurement system is configured to measure light transmitted through disk 112. In this alternative embodiment, the beam splitter 102 may be removed or replaced with a polarizer. Additional optical elements such as mirrors and lenses can be used if desired to direct the transmitted light to the detector.

Light source 100 outputs generally monochromatic or quasi-monochromatic light along optical path 118.
Suitable light sources include mercury lamps, light emitting diodes, diode lasers and the like. Optical path 118 passes through beam splitter 102. The transmitted light follows the split light path 120. If the detection system is sensitive to polarized light, a partially polarized beam splitter can be used. For example the light source polarization rate (I _p vs. I _s) is relatively low, as long as such as a laser diode having an approximately 100: 1 polarization ratio, even if the light source 100 is not polarized, a polarizing beam The polarization ratio can be increased by using a splitter. When a partially polarized beam splitter is used, light transmitted along split path 120 is partially plane polarized. Light with partially orthogonal polarization is reflected at 90 degrees to the direction of incidence.
The reflected incident light is directed to power system 16 if desired.

The transmitted light continues along the optical path 120 to the slider 104. Referring to FIG. 2, slider 104 is generally at the end of arm 122, which may be a flexible spring suspension arm. The slider 104 includes an objective lens 124. Objective lens 124 can be mounted on slider base 126 using spacer 128. The slider 104 is an optional slider optical instrument 1
30. Slider optics 130 helps optically couple objective lens 124 to the surface of disk 110 to minimize distortion due to refractive index changes. Suitable slider optics 130 include a solid immersion lens (SIL) or the like. Preferably, the slider is part of a near-field optical recording head. Objective lens 1
Reference numeral 24 is arranged within the range of the split optical path 120 to generate a focused optical path 132.

Referring to FIG. 1A, light passing through the optical element of the slider 104
12 from the surface 110. The reflected light passes through the optical elements of the slider 104 including the objective lens 124 and returns. This reflected light continues to beam splitter 102. In beam splitter 102, a portion of this reflected light is directed 90 degrees along detection path 140, as shown in FIG. 1A. The detection path 140 intersects with the detection module 106.

With a suitable disk, a portion of the light is transmitted through disk 112. In an alternative embodiment, shown in FIG. 1B, the transmitted light path 142 is directed to detector 106.

Disk 112 is typically a test disk specially designed for distance measurement. The surface properties can be selected based on the attributes of the detector module 106 and the type of measurement corresponding thereto. In particular, the surface 110 of the disk 112 can be transparent or reflective. Further, the surface 110 of the disk 112 may have a coating if appropriate. If desired, pre-embossed media having holes or grooves can be used. Also, a portion of the data storage disk may have a specific portion used as a test disk.

In particular, one embodiment of the disk 112 is a reflective aluminum coated disk. This aluminum coated disc is optional
It may include a thin layer of an optically transparent material such as iN. The thin film generally has a thickness on the order of one wavelength or less. The thickness of the SiN layer changes the attributes of the reflected light. In addition, the air incident surface of SiN can be coated with a lubricant.

Another embodiment of the disk 112 includes a glass disk with or without a thin film layer such as SiN. For this type of disc, reflectivity is a particularly suitable measurement for determining fly height. A third embodiment of the test disk 112 is an optical stack that includes a magneto-optical (MO) medium.
ack) is a disk coated with glass or aluminum.

Some attributes of the reflected (transmitted) light are
It depends on the distance to 12. Detector module 106 may include elements that measure one or more of these distance-dependent attributes and provide output to processor 108, for example, via cable 144. If necessary, an analog-to-digital converter or other signal conditioner may be included to prepare the signal for processor 108. The selection of an appropriate detection method and test disk will be based on acceptable tolerances on fly height and the range of expected deviations from acceptable values of fly height.

The disk is rotated at a constant speed to perform the measurement. After a short transition period, the slider acquires a relatively constant height above the disk. Then the measurement is performed. The optical head is aligned with the optical path by minimizing the light reflected back to the detector module. In general, the output of the detector module presented herein correlates to fly height. Using an alternative fly height measurement technique, a correlation is obtained, which is stored in the memory 146 of the processor 108.

Three embodiments of the detector module 106 are shown in FIGS. Referring to FIG. 3, a first embodiment of the detector module 106 includes an optional slit aperture 15
0, a lens 152, an optional iris stop 154, and a two-element detector 156. The slit opening 150 can reduce noise. Lens 152 focuses the light on detector 156. The optional iris stop 154 is connected to the lens 15 in the optical path.
It can be placed before or after 2. In FIG. 3, the iris diaphragm 1
54 is located behind the lens 152 between the lens 152 and the two-element detector 156. The iris stop 154 is a half (50%) aperture stop (apertur
e stop) can be used for a central aperture stop. The iris stop 154 generally reduces the contribution of reflected light near normal incidence with respect to the disk surface and increases the contribution of light waves having relatively high angles of incidence.

The element detector 154 has photosensitive elements 158 (A) and 160 (B). The focus signal can be defined as the difference between the measured values of the two photosensitive elements, focus signal = AB.
The focus signal can be correlated to the distance of the disk 110 to the slider 104.

FIG. 4 shows a second embodiment of the detector module 106. In this example,
The detector module 106 includes an iris diaphragm and an optional wave plate (wavepla).
te), polarizing beam splitter 174, photosensitive elements 176 (C), 178 (D
) Includes a central aperture stop. The different polarizations generally reflect differently from the surface of disk 110. The difference in reflectivity generally depends on the distance between the slider 104 and the disk 110. The difference in the reflection attribute of the deflected light appears in the difference between the measured values of the photosensitive elements 176 and 178. These differences can be expressed as polarization ratio = C / D or polarization difference CD. This configuration of the detector module 106 can also be used to obtain a value proportional to the total amount of reflected light by adding (C + D) the measurements of the elements 176, 178. A wave plate 172 can be used to change the polarization of the light following path 140 before hitting the polarizing beam splitter 174. For example, the wave plate may be a half wave plate arranged at 22.5 degrees or a quarter wave plate arranged at 45 degrees.

Referring to FIG. 6, the polarization as a function of flying height has been evaluated using an aluminum coated disk using the experimental apparatus shown schematically in FIG. 1A. Polarization index is defined as the ratio of y-polarized light to x-polarized light in the reflected beam when the incident light is purely x-polarized. The objective lens is 0.
The SIL has a numerical aperture of 65 and the SIL has a numerical aperture of 2.15. The RIM intensity at the objective lens is 0.28.

As shown in FIG. 6, the effect of SiN thickness on aluminum coated disks is also evaluated in terms of polarization (PR) as a function of flying height. Different S
The iN thickness produces a PR curve as a function of flying height with areas of different effect corresponding to areas where the curve varies monotonically. Once the fly height and PR correlation is established, this correlation can be stored and used for subsequent fly height measurements. Similarly, using disks separated by zones with several different SiN thicknesses, for a particular SiN thickness within its effective measurement range, the flying height can be increased to 500 nm without the need for a monotonic curve. Above the range, measurements can be made with good accuracy. FIG.
Referring to, measurements obtained with different numerical apertures of the objective lens demonstrate that this technique can accept a wide range of numerical apertures.

FIG. 8 plots the measured reflection percentage as a function of flying height for five different thicknesses of SiN. The reflectivity has been measured with respect to a power meter reading corresponding to element 114 of FIG. The reflectance curve has a monotonic range of about 250 nm for a specific numerical aperture of the objective lens. Referring to FIG. 9, the effective measurement range of the reflectance measurement is a gradual function of the numerical aperture, since the flying height does not change significantly for several different values of the numerical aperture at the initial maximum of the reflectance.

As shown in FIG. 3, by adding a central aperture stop prior to the detector in the incident light or reflected beam, the measurement range can be greatly improved. The effect of the 50% stop on the reflectance measurements is seen in FIG. The lens for these measurements is S
No iN coating. This 50% stop corresponds to a pupil radius of 0.707 for a maximum clear aperture radius of 1.0. For a numerical aperture of 0.65, this 50
A percent aperture increases the effective measurement range by about 500 nm. Referring to FIG. 11, the polarization as a function of fly height is obtained at 50% aperture for two aluminum coated disks with different SiN thickness. This 50% stop greatly enhances the sensitivity of the polarization measurements.

Referring to FIG. 12, a measurement of the polarization difference is made as a function of flying height with a disk coated with an optical stack containing MO media. FIG. 13 shows similar measured values of the reflection percentage (REF), the total percentage, and the polarization ratio. "Reflectance" is the overall intensity of the beam returning through the lens, and "Total" is the overall intensity measured after reflection from the partially polarized beam splitter. These measurements were made at a 50% stop in the reflected beam. All of the measurements shown in FIGS. 14 and 15 show good properties indicating that they are appropriate for measurements up to a fly height of about 500 nm.

A third embodiment of the detector module 106 is shown in FIG. In this embodiment, detector module 106 includes optional slit aperture 190, polarizer 19
2, including a detector array 194. This embodiment may also include an iris stop.
For initial polarization according to the desired measurement, polarizer 192 is preferably oriented at 0, 45, or 90 degrees. To measure the brightness distribution of the various polarization states, the polarizer is rotated between a preferred value and various other values. Similar information is obtained from the measurements with the polarizer and from the second measurement without the polarizer. Detector array 194 can be a CCD array or any other photosensitive array or appropriate dimension. Detector array 194 may have a one-dimensional or two-dimensional array of photosensitive elements. The luminance pattern measured by the detector array 194
The distance between the disk 112 and the disk 112.

Other measurements, such as intensity distribution, phase distribution, polarization distribution, can be used to assess fly height. FIG. 14 illustrates the intensity distribution of the x-polarized field component of the reflected beam obtained with an aluminum-coated test disk and x-polarized incident light. These measurements can be made using an array detector. The intensity distribution is shown for four flying heights. Similarly, FIG. 15 illustrates the phase distribution of the x-polarized field component of the reflected beam for four fly heights. Since the intensity distribution and the phase distribution differ depending on the flying height, they can be used for calculating the flying height. In the case of the phase distribution, the measurement based on the focus sensor of the detector module of FIG. 3 is a measurement that is particularly suitable for calculating the flying height.

The embodiments described above are intended to be representative, but not limiting. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. The terms "light" or "optical" as used herein refer to radiation of any wavelength and are not limited to visible radiation.

[Brief description of the drawings]

FIG. 1A is a schematic diagram illustrating a measurement system for determining a slider distance with respect to a rotating disk.

FIG. 1B is a schematic diagram illustrating another embodiment of a measurement system for determining a slider distance with respect to a rotating disk.

FIG. 2 is a side cross-sectional view of the slider and its support arm, having a cross-section taken through the center of the slider.

FIG. 3 is a schematic side view of an embodiment of a detector module with two photosensitive elements for use in the measurement system of FIG. 1, wherein any covering is transparent to expose the internal components of the detector module; It is made in.

FIG. 4 is a schematic side view of an embodiment of a detector module with a polarizing beam splitter for use in the measurement system of FIG. 1, wherein any covering is transparent for exposing the internal components of the detector module. It is made in.

FIG. 5 is a schematic side view of an embodiment of a detector module incorporating an array detector for use in the measurement system of FIG. 1, wherein any shroud is used to expose the internal components of the detector module. Made transparent.

FIG. 6 shows five different SiNs on the surface of an aluminum coated test disk
5 is a plot of polarization as a function of flying height for thickness.

FIG. 7 is a plot of the polarization as a function of flying height for a plurality of different numerical apertures of the objective lens.

FIG. 8 is a plot of percent reflection as a function of flying height for five different SiN thicknesses on a glass test disk.

FIG. 9 is a plot of percent reflection as a function of flying height for five different numerical apertures of the objective lens.

FIG. 10 is a plot of percent reflection as a function of flying height with or without 50% aperture.

FIG. 11 is a plot of the percent reflection as a function of flying height with or without 50% aperture for two different SiN thicknesses on the test disk.

FIG. 12 is a plot of the difference in polarization as a function of flying height for a disk with an optical stack of magneto-optical material.

FIG. 13 is a plot of percent reflection, polarization and polarization as a function of flying height obtained with a disk having an optical stack of magneto-optical material.

FIG. 14 shows x-polarized incident fields for four different flying heights above an aluminum coated disk: a) flying height of 0 nm, b) flying height of 100 nm, c) flying height of 200 nm, d) flying height of 400 nm. 2 is a two-dimensional plot of the intensity of the x-polarized light component of the reflected light obtained following the reflection of.

FIG. 15 shows x-polarized incident fields for four different flying heights above an aluminum coated disk: a) 0 nm flying height, b) 100 nm flying height, c) 200 nm flying height, and d) 400 nm flying height. 2 is a two-dimensional plot of the phase of the x-polarized light component of the reflected light obtained following the reflection of.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventors Mauri, Gregory, S United States Minnesota, Burnsville, Geneva Boulevard 18F term (reference) 2F064 AA00 BB00 FF02 GG22 GG23 GG38 GG39 HH05 JJ01 2F065 AA22 BB03 GG03 GG51 GG03 JJ26 LL36 LL37 LL46 QQ03 QQ27 QQ28

Claims (20)

[Claims] 1. A flying height measurement system for measuring a flying height of a slider on a storage disk, comprising: means for focusing light near a bottom of the slider; and a light propagating from a disk pivoting directly below the slider. Means for estimating the flying height based on the light emitted. 2. A flying height measuring system for measuring a flying height of a slider on a storage disk, comprising: a light source for generating light along one optical path; and a light from the light source impinging on an objective lens, and a surface of the disk. A slider including one of said objective lenses arranged to be directed to a light source; a detector module for receiving light reflected from a disk; and a processor for estimating a flying height of the slider based on an output of the detector module. Fly height measurement system including: 3. The measurement system according to claim 2, wherein the light from the light source is monochromatic or quasi-monochromatic. 4. The measurement system according to claim 2, further comprising a beam splitter in an optical path between the light source and the objective lens. 5. The measurement system according to claim 4, wherein said beam splitter is a partially polarized beam splitter. 6. The measurement system of claim 2, wherein said slider further comprises a solid immersion lens such that said light is coupled to said disk surface through a nearby field. 7. The measurement system according to claim 2, wherein said light source includes a red laser. 8. The measurement system according to claim 2, wherein the detector module includes one lens and one two-element detector. 9. The measurement system according to claim 2, wherein the detector module includes a polarizer. 10. The measurement system according to claim 2, wherein said detector module comprises a detector array. 11. The detector module of claim 2, wherein the detector module includes a polarization beam splitter and two photosensitive elements each configured to measure one component of the split beam. Measurement system. 12. The measurement system according to claim 2, wherein said detector module includes one central aperture stop. 13. The detector module outputs a signal related to the total amount of reflected light received by the detector module, and the processor outputs a signal between the detector module output and information stored in a memory. The measurement system according to claim 2, wherein the flying height is estimated based on the comparison. 14. The detector module outputs a signal related to the polarization of the reflected light received by the detector module, and the processor outputs a signal between the output of the detector module and information stored in memory. The measurement system according to claim 2, wherein the flying height is estimated based on the comparison. 15. The measurement system according to claim 14, wherein the polarization ratio of the reflected light is evaluated. 16. The detector module outputs one signal relating to the distribution of the intensity, phase, and polarization of the reflected light received by the detector module, and the processor stores the signal in the memory with the output of the detector module. The measurement system according to claim 2, wherein the flying height is estimated based on comparison with information stored in the storage device. 17. A flying height measuring system for measuring a flying height of a slider on a storage disk, comprising: a light source for generating light along one optical path; and a light from the light source impinging on an objective lens, and a surface of the disk. A slider including one of said objective lenses arranged to be directed to a detector module for receiving light reflected through a disk, wherein said light directed to said detector is based on wavelength. A flying height measurement system that includes a detector module that is not spatially dispersed and a processor that estimates a flying height of a slider based on an output of the detector module. 18. The detector module of claim 17, wherein the detector module includes a polarization beam splitter and two photosensitive elements each configured to measure one component of the split beam. Measurement system. 19. The measurement system according to claim 17, wherein said detector module includes one central aperture stop. 20. The measurement system according to claim 17, wherein said detector module comprises a detector array.