Author: claimsbot

1. A method for depositing a film on a substrate that is within a reaction chamber, the method comprising applying an atomic layer deposition cycle to the substrate, the cycle comprising:
exposing the substrate to a first precursor gas pulse sequence, wherein the first precursor gas sequence includes:
exposing the substrate to a first precursor gas for a first precursor pulse interval then removing the first precursor gas thereafter; and
exposing the substrate to a first oxidant gas for a first oxidation pulse interval then removing the first oxidation gas thereafter;

exposing the substrate to a second precursor gas pulse sequence, wherein the second sequence includes:
exposing the substrate to a second precursor gas for a second precursor pulse interval then removing the second precursor gas thereafter; and
exposing the substrate to a second oxidant gas for a second oxidation pulse interval then removing the second oxidation gas thereafter;

wherein the first precursor gas comprises at least one of tetrakis-ethyl-methylamino hafnium (TEMAHf) and lanthanum tris-formamidinate (LaFAMD)3.
2. The method of claim 1 wherein the second precursor gas comprises at least one of tetrakis-ethyl-methylamino hafnium (TEMAHf) and lanthanum tris-formamidinate (LaFAMD)3.
3. The method of claim 1 wherein the first precursor gas comprises TEMAHf and the second precursor gas comprises (LaFAMD)3.
4. The method of claim 1 wherein the first oxidant gas and the second oxidant gas comprise one or more of the group selected from O, O2, O3, H2O, H2O2, NO, N2O, N2O5 and NO2.
5. The method of claim 2 wherein each of the first oxidant gas and the second oxidant gas comprises O2 and O3.
6. The method of claim 5 wherein each of the first oxidant gas and the second oxidant gas comprises approximately 10 atomic percent to 20 atomic percent O3.
7. The method of claim 5 wherein each of the first oxidant gas and the second oxidant gas comprises approximately 12 atomic percent to 18 atomic percent O3.
8. The method of claim 1 further comprising repeating the atomic layer deposition cycle until the deposited film has reached a predetermined thickness.
9. The method of claim 1 further comprising in any atomic layer deposition cycle:
performing the first precursor gas pulse sequence a predetermined number of n iterations; and
performing the second precursor gas pulse sequence a predetermined number of m iterations, wherein the ratio of n:m is 1:1.
10. The method of claim 9 wherein the ratio if n:m is greater than 1.
11. The method of claim 9 wherein the ratio if n:m is less than 1.
12. The method of claim 9 wherein the n iterations of the first precursor gas sequence are performed before the m iterations of the second precursor gas sequence.
13. The method of claim 9 wherein the number of n iterations and the number of m iterations are determined by at least one of:
a dielectric constant of the deposited film;
an index of refraction of the deposited film;
a molecular composition of the deposited film; and
a ratio of atomic hafnium to atomic lanthanum to be deposited in the deposited film.
14. The method of claim 1 wherein:
the first precursor pulse interval is in the range of 300 milliseconds to 5 seconds;
the first oxidation pulse interval is in the range of 50 milliseconds to 10 seconds;
the second precursor pulse interval is in the range of 500 ms to 10 seconds; and
the first oxidation pulse interval is in the range of 50 milliseconds to 10 seconds.
15. The method of claim 1 wherein:
the first precursor pulse interval is in the range of 1 second to 2 seconds;
the first oxidation pulse interval is in the range of 50 milliseconds to 2 seconds;
the second precursor pulse interval is in the range of 1 second to 4 seconds; and
the first oxidation pulse interval is in the range of 50 milliseconds to 2 seconds.
16. The method of claim 1 wherein the first precursor gas sequence deposits a first sequence film on the substrate wherein the first sequence film is deposited with a thickness between 0.8-1.1 \u212b per first precursor gas sequence.
17. The method of claim 1 wherein the second precursor gas sequence deposits a second sequence film on the substrate wherein the second sequence film is deposited with a thickness between 0.6-0.8 \u212b per second precursor gas sequence.
18. The method of claim 1 wherein the film deposited by the atomic layer deposition cycle deposits the film with a thickness between 1.4-2.7 \u212b per deposition cycle.
19. The method of claim 1 wherein during the atomic layer deposition cycle, the substrate is maintained at a temperature in the range of 140\xb0 C. to 300\xb0 C.
20. The method of claim 1 wherein during the atomic layer deposition cycle, the substrate is maintained at a temperature in the range of 175\xb0 C. to 250\xb0 C.
21. The method of claim 1 wherein during the atomic layer deposition cycle, a vessel temperature of at least one of the first precursor gas and the second precursor gas is maintained at a temperature in the range of 135\xb0 C. to 145\xb0 C.
22. The method of claim 1 wherein removing the first precursor gas, removing the first oxidation gas, removing the second precursor gas and removing the second oxidation gas comprises at least one of:
evacuating gas from the reaction chamber for a predetermined evacuation period; and
introducing a purge gas into the reaction chamber for a purge period, wherein:
the purge gas comprises one or more of the group consisting of: argon, nitrogen, helium, hydrogen, forming gas, krypton, and xenon; and
the purge period is in the range of approximately 500 milliseconds to 10 seconds.
23. The method of claim 22 wherein the purge period is in the range of approximately 500 milliseconds to 4 seconds.
24. The method of claim 22 wherein the purge period is in the range of approximately 3 seconds to 10 seconds.
25. A method for depositing a film on a substrate that is within a reaction chamber, the method comprising applying an atomic layer deposition cycle to the substrate, the cycle comprising:
exposing the substrate to a first precursor gas pulse sequence, wherein the first sequence includes:
exposing the substrate to a first precursor gas comprising tetrakis-ethyl-methylamino hafnium (TEMAHf) for a first precursor pulse interval;
removing the first precursor gas by introducing a purge gas into the reaction chamber for a first precursor purge period;
exposing the substrate to a first oxidant gas for a first oxidation pulse interval; and
removing the first oxidant gas by introducing the purge gas into the reaction chamber for a first oxidant purge period;

exposing the substrate to a second precursor gas pulse sequence, wherein the first sequence includes:
exposing the substrate to a second precursor gas comprising Lanthanum tris-formamidinate (LaFAMD)3 for a second precursor pulse interval;
removing the first precursor gas by introducing the purge gas into the reaction chamber for a second precursor purge period;
exposing the substrate to a second oxidant gas for a second oxidation pulse interval; and
removing the second oxidant gas by introducing the purge gas into the reaction chamber for a second oxidant purge period.
26. The method of claim 25 wherein each of the first oxidant gas and the second oxidant gas comprises a mixture of O2 and O3, and wherein the mixture comprises approximately 10 atomic percent to 18 atomic percent O3.
27. The method of claim 25 further comprising repeating the atomic layer deposition cycle until the deposited film has reached a predetermined thickness.
28. The method of claim 25 further comprising repeating the first precursor gas pulse sequence a plurality of times before exposing the substrate to the second precursor gas sequence.
29. The method of claim 25 wherein:
the first precursor pulse interval is in the range of about 1 second to 2 seconds;
the first oxidation pulse interval is in the range of 50 milliseconds to 2 seconds;
the second precursor pulse interval is in the range of 1 second to 4 seconds; and
the first oxidation pulse interval is in the range of 50 milliseconds to 2 seconds.
30. The method of claim 25 wherein during the atomic layer deposition cycle, the substrate is maintained at a temperature in the range of 175\xb0 C. to 250\xb0 C.
31. The method of claim 25 wherein during the atomic layer deposition cycle, a vessel temperature of a vessel holding at least one of the first precursor gas and the second precursor gas is maintained at a temperature in the range of 135\xb0 C. to 145\xb0 C.
32. An electronic device comprising a HfLaO dielectric layer and a conductive layer in communication with the dielectric layer, the dielectric layer deposited in a film by
applying an atomic layer deposition cycle according to claim 1 to the substrate.
33. The electronic device of claim 32 wherein the first oxidant gas and the second oxidant gas comprise a mixture of O2 and O3, and wherein the mixture comprises approximately 12 atomic percent to 18 atomic percent O3.
34. The electronic device of claim 32 further comprising repeating the atomic layer deposition cycle until the dielectric layer has reached a predetermined thickness.
35. The electronic device of claim 32 further comprising repeating the first precursor gas pulse sequence a plurality of times before exposing the substrate to the second precursor gas sequence.
36. The electronic device of claim 32 wherein:
the first precursor pulse interval is in the range of 1 second to 2 seconds;
the first oxidation pulse interval is in the range of 50 milliseconds to 2 seconds;
the second precursor pulse interval is in the range of 1 second to 4 seconds; and
the first oxidation pulse interval is in the range of 50 milliseconds to 2 seconds.
37. The electronic device of claim 32 wherein during the atomic layer deposition cycle, the substrate is maintained at a temperature in the range of 175\xb0 C. to 250\xb0 C.
38. The electronic device of claim 32 a vessel temperature of a vessel holding at least one of the first precursor gas and the second precursor gas is maintained at a temperature in the range of 135\xb0 C. to 145\xb0 C.
39. The electronic device of claim 32 wherein the electronic device comprises at least one of a capacitor, a transistor, a FLASH memory cell, and a DRAM memory cell.
40. An electronic system comprising:
a processor;
a memory device coupled to the processor, wherein the memory device includes a plurality of transistors, wherein the transistors include an HfLaO dielectric layer and a conductive layer in communication with the dielectric layer, the dielectric layer deposited in a film by applying an atomic layer deposition cycle according to claim 1 to the substrate.
41. The electronic device of claim 40 wherein the first oxidant gas and the second oxidant gas comprise a mixture of O2 and O3, and wherein the mixture comprises approximately 12 atomic percent to 18 atomic percent O3.
42. The electronic device of claim 40 further comprising repeating the atomic layer deposition cycle until the dielectric layer has reached a predetermined thickness.
43. The electronic device of claim 40 further comprising repeating the first precursor gas pulse sequence a predetermined plurality of times before exposing the substrate to the second precursor gas sequence.
44. The electronic device of claim 40 wherein:
the first precursor pulse interval is in the range of 1 second to 2 seconds;
the first oxidation pulse interval is in the range of 50 milliseconds to 2 seconds;
the second precursor pulse interval is in the range of 1 second to 4 seconds; and
the first oxidation pulse interval is in the range of 50 milliseconds to 2 seconds.
45. The electronic device of claim 40 wherein during the atomic layer deposition cycle, the substrate is maintained at a temperature in the range of 175\xb0 C. to 250\xb0 C.
46. The electronic device of claim 40 a vessel temperature of a vessel holding at least one of the first precursor gas and the second precursor gas is maintained at a temperature in the range of 135\xb0 C. to 145\xb0 C.
47. The electronic device of claim 40 wherein the electronic system comprises at least one of a computer, a mobile subscriber unit such as a cellular telephone or smart phone, and a PDA.

The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.

1. A coupling assembly for providing a fluid connection comprising:
a female connector defining a bore, said bore extending axially inwardly into said connector from an entrance, an annular face being defined in said bore axially inwardly of said entrance;
a tube received within said bore with an enlarged upset;
a retainer disposed in said bore having a member directly contacting said upset and extending to said annular face to retain said tube in said bore; and
a cap slidable mounted on said tube and attached to said female connector, said cap having a protrusion directly contacting said upset.
2. The coupling assembly as claimed in claim 1 wherein said cap further has an arm abutting said annular face for attaching said cap to said female connector.
3. The coupling assembly as claimed in claim 1 wherein said protrusion is a beam extending axially.
4. The coupling assembly as claimed in claim 1 wherein said cap further has a portion surrounding said entrance of said female connector.
5. The coupling assembly as claimed in claim 4 wherein said portion of said cap has a diameter at least as large as the outer diameter of said female connector radially outward of said entrance.
6. The coupling assembly as claimed in claimed in claim 1 further comprising an O-ring sealingly engaging said tube axially inward of said upset.
7. The coupling assembly as claimed in claim 1 wherein said retainer has four members.
8. The coupling assembly as claimed in claim 2 wherein said protrusion is located ninety degrees from said arm.
9. A coupling assembly for providing a fluid connection comprising:
a female connector defining a bore, said bore extending axially inwardly into said connector from an entrance, an annular face being defined in said bore axially inwardly of said entrance;
a tube received within said bore with an enlarged upset;
a retainer disposed in said bore having a member directly contacting said upset and extending to said annular face to retain said tube in said bore; and
a cap slidable mounted on said tube having a portion surrounding said entrance of said female connector and an arm abutting said annular face for attaching said cap to said female connector.
10. The coupling assembly as claimed in claim 9 wherein said portion of said cap has a diameter at least as large as the outer diameter of said female connector radially outward of said entrance.
11. A coupling assembly as claimed in claimed in claim 9 further comprising an O-ring sealingly engaging said tube axially inward of said upset.
12. A coupling assembly as claimed in claimed in claim 9 wherein said retainer has four members.
13. A release tool for removing a tubing with an enlarged upset received within a bore extending axially inwardly into a female connector, a retainer disposed in said bore having a member directly contacting said upset and extending to an annular face defined in said bore axially inward of said entrance to retain said tube in said bore, said release tool slidably mounted on said tubing having a reduced diameter portion and an enlarged diameter portion, said reduced diameter portion of said release tool having an outer diameter at least as large as the diameter of said upset, wherein insertion of said reduced diameter portion of said release tool into said bore expands said member radially outward.
14. The release tool as claimed in claim 13 wherein said enlarged diameter portion has an inner diameter at least as large as the outer diameter of said female connector radially outward of said entrance.

1. A rust-preventive steel sheet for fuel tanks, excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises
a steel sheet comprising, in terms of % by weight, up to 0.01% of C, up to 0.2% of Si, less than 0.6% of Mn, up to 0.04% of P, up to 0.1% of soluble Al, up to 0.01% of N, at least one of Ti and Nb in a total amount of at least the atomic equivalent of (CN) and up to 0.2%, 0.0001 to 0.0030% of B, and the balance Fe and unavoidable impurities, and
a plating layer comprising 2 to 13% of Si in terms of % by weight, and the balance Al and unavoidable impurities on the surface of the steel sheet.
2. A rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises
a steel sheet comprising, in terms of % by weight, up to 0.01% of C, up to 0.2% of Si, less than 0.6% of Mn, up to 0.04% of P, up to 0.1% of soluble Al, up to 0.01% of N, one or at least two of Ti and Nb in a total amount of at least the atomic equivalent of (CN) and up to 0.2%, 0.0003 to 0.0030% of B, and the balance Fe and unavoidable impurities, and
a plating layer comprising 2 to 13% of Si in terms of % by weight, and the balance Al and unavoidable impurities on the surface of the steel sheet.
3. A rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises
a steel sheet comprising, in terms of % by weight, up to 0.003% of C, up to 0.1% of Si, up to 0.4% of Mn, up to 0.02% of P, up to 0.1% of soluble Al, up to 0.01% of N, at least one of Ti and Nb in a total amount of at least the atomic equivalent of (CN) and up to 0.2%, 0.0003 to 0.0030% of B, and the balance Fe and unavoidable impurities, and
a plating layer comprising 2 to 13% of Si in terms of % by weight, and the balance Al and unavoidable impurities on the surface of the steel sheet.
4. A rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises
a steel sheet comprising, in terms of % by weight, up to 0.003% of C, up to 0.03% of Si, up to 0.3% of Mn, up to 0.02% of P, up to 0.006% of soluble N, up to 0.1% of Ti, and the balance Fe and unavoidable impurities, and
a plating layer comprising 2 to 13% of Si in terms of % by weight, and the balance Al and unavoidable impurities on the surface of the steel sheet,
the steel sheet showing a total elongation of at least 45% after plating.
5. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to any one of claims 1 to 4, wherein the steel sheet comprises at least one element selected from the following group in the following amounts: 0.5 to 7% of Cr, 0.05 to 0.5% of Cu, 0.05 to 0.5% of Ni and 0.05 to 0.5% of Mo.
6. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to any one of claims 1 to 5, wherein the amount of the Al plating layer is up to 50 gm2 per side.
7. A rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming, which comprises a steel sheet substrate for plating, an AlFeSi intermetallic compound layer thereon and a plating layer comprising Al and unavoidable impurities on the intermetallic compound layer, the difference between the immersion potential of the steel sheet substrate for plating and that of the intermetallic compound layer in a solution comprising 100 ppm of formic acid and the balance water and unavoidable impurities being up to 0.35 V.
8. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to claim 7, wherein the AlSi plating layer comprises 2 to 13% of Si, 0.5 to 5% in total of one or at least two elements selected from the group consisting of Sn, Zn, Sb and Bi, and the balance Al and unavoidable impurities.
9. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to any one of claims 1 to 8, wherein the rust-preventive steel sheet comprises a chromate coating layer in an amount of 5 to 100 mgm2 as Cr per side at least on one side of the Al plating layer.
10. The rust-preventive steel sheet for fuel tanks excellent in air-tightness after welding and corrosion resistance subsequent to forming according to any one of claims 1 to 9, wherein the rust-preventive steel sheet comprises an organic resin coating layer on the top surface at least on one side thereof.

The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.

1. An optical pickup for recording andor reproducing data with respect to a multilayer recording medium having a plurality of recording layers, the optical pickup comprising:
a light source emitting a beam having a predetermined wavelength;
a diffraction unit separating the beam emitted from the light source into a main beam and a sub-beam; and
a photo-detector having a main photodetector, detecting the main beam reflected from the multilayer recording medium, and a sub-photodetector detecting the sub-beam,
wherein the main photodetector and the sub-photodetector are separated a predetermined distance Ds from each other so that a beam spot formed by the beam reflected from a defocus recording layer of the multilayer recording medium is not detected by the sub-photodetector, and
wherein the predetermined distance Ds between the main photodetector and the sub-photodetector satisfies the following inequality:
Ds\u2267A2+QR
wherein \u201cR\u201d is a radius of the beam spot formed by the beam reflected from the defocus recording layer, \u201cA\u201d is a width of the sub-photodetector, and \u201cQ\u201d is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, and
wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.
2. The optical pickup as claimed in claim 1, wherein the radius R satisfies the following equation:
R
=

2
\xd7
d
sp
n
sp
\xd7
M
\xd7
NA
,
wherein, \u201cdsp\u201d is a thickness of a spacer layer between the defocus recording layer and a recording layer that is subject to recording andor reproduction, \u201cnsp\u201d is a refractive index of the spacer layer, \u201cM\u201d is a magnifying power of the optical pickup, and \u201cNA\u201d is a numerical aperture of an objective lens used in the optical pickup.
3. The optical pickup as claimed in claim 1, wherein the main photodetector is a four-section photodetector.
4. The optical pickup as claimed in claim 1, wherein the sub-photodetector is a two-section photodetector.
5. The optical pickup as claimed in claim 1, further comprising a calculation portion calculating signals detected by the main photodetector and the sub-photodetector and outputting a differential push-pull signal.
6. A method of setting an optical pickup including a light source emitting a beam having a predetermined wavelength, a diffraction unit separating the beam emitted from the light source into a main beam and a sub-beam, and a photodetector having a main photodetector, detecting the main beam reflected from a multilayer recording medium, and a sub-photodetector detecting the sub-beam, the method comprising:
setting a distance Ds between the main photodetector and the sub-photodetector to satisfy the following inequality, to prevent a beam spot formed by the main beam from being detected by the sub-photodetector:
D
s

\u2265
A
2

+
QR
,
wherein \u201cR\u201d is a radius of the beam spot formed by the beam reflected from a defocus recording layer, \u201cA\u201d is a width of the sub-photodetector, and \u201cQ\u201d is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, and
wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.
7. The method as claimed in claim 6, wherein the radius R satisfies the following equation:
R
=

2
\xd7
d
sp
n
sp
\xd7
M
\xd7
NA
,
wherein, \u201cdsp\u201d is a thickness of a spacer layer between the defocus recording layer and a recording layer that is subject to recording andor reproduction, \u201cnsp\u201d is a refractive index of the spacer layer, \u201cM\u201d is a magnifying power of the optical pickup, and \u201cNA\u201d is a numerical aperture of an objective lens used in the optical pickup.
8. An optical pickup for use with a multilayer recording medium having a plurality of recording layers that are subject to recording andor reproduction, the optical pickup comprising:
a photodetector having a main photodetector and a sub-photodetector, wherein, when a distance between the main photodetector and the sub-photodetector is Ds, the distance Ds satisfies the following inequality:
d
sp

\u2264
(
D
s

–

A
2
)

\xd7

n
sp
2
\u2062
Q
\xd7
M
\xd7
NA
,
wherein \u201cA\u201d is a width of the sub-photodetector, \u201cQ\u201d is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, \u201cnsp\u201d is a refractive index of a spacer layer between the plurality of recording layers, \u201cM\u201d is a magnifying power of the optical pickup, and \u201cNA\u201d is a numerical aperture of an objective lens used for the optical pickup.
9. The optical pickup as claimed in claim 8, wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.
10. The optical pickup as claimed in claim 8, wherein the optical pickup performs a tracking servo control using a differential push-pull method.
11. The optical pickup as claimed in claim 9, wherein the coefficient indicating the allowable range of the DC offset is determined based on the range of the DC offset of the sub-push-pull signal.
12. The optical pickup as claimed in claim 1, wherein the light source is configured to emit a beam in a blue wavelength range.
13. The optical pickup as claimed in claim 1, wherein the optical pickup uses a differential push-pull (DPP) method for tracking servo control.
14. The optical pickup as claimed in claim 2, wherein the numerical aperture of the objective lens is approximately 0.85.
15. The method of claim 6, comprising detecting a radial tilt signal from the multilayer recording medium, preventing crosstalk created by the beam reflected from the defocus layer.
16. An optical pickup for recording andor reproducing data with respect to a multilayer recording medium having a plurality of recording layers, the optical pickup comprising:
a light source emitting a beam having a predetermined wavelength;
a diffraction unit separating the beam emitted from the light source into a main beam and at least one sub-beam; and
a photodetector having a main photodetector, detecting the main beam reflected from the multilayer recording medium, and at least one sub-photodetector detecting the at least one sub-beam,
wherein the main photodetector and the at least one sub-photodetector are separated a predetermined distance from one another preventing a defocus spot, formed by the beam reflected by a defocus recording layer adjacent to a recording layer that is subject to recording andor reproduction, from being detected by the at least one sub-photodetector, and
wherein an outer border of the defocus spot is tangential to an outer area of the sub photodetector that is not contacted by the sub-beam, and
wherein the predetermined distance between the main photodetector and the at least on sub-photodetector satisfies the following inequality:
Ds\u2267A2\u2212QR
wherein \u201cR\u201d is a radius of the beam spot formed by the beam reflected from the defocus recording layer, \u201cA\u201d is a width of the sub-photodetector, and \u201cQ\u201d is a coefficient indicating an allowable range of a DC offset of a sub-push-pull signal, and
wherein the coefficient Q is between 0.85-0.90 when the allowable range of the DC offset is not more than 5%.
17. The optical pickup as claimed in claim 16, wherein the radius R of the beam spot satisfies the following equation:
R
=

2
\u2a2f
d
sp
n
sp
\u2a2f
M
\u2a2f
NA
,
wherein, \u201cdsp\u201d is a thickness of a spacer layer between the defocus recording layer and a recording layer that is subject to recording andor reproduction, \u201cnsp\u201d is z refractive index of the spacer layer, \u201cM\u201d is z magnifying power of the optical pickup, and \u201cNA\u201d is z numerical aperture of an objective lens used in the optical pickup.
18. The optical pickup as claimed in claim 16, wherein the DC offset of the sub-push-pull signal decreases as the predetermined distance between the main photodetector and the at least one sub-photodetector increases.