Main
properties of sapphire:
| Chemical
formula |
Al2O3 |
| Crystal
class |
Hexagonal
system, rhomboidal class 3m |
| Lattice
constants, A |
a=4.785,
c=12.991 |
| Density,
g/cm3 |
3.98 |
| Melting
point, °K |
2303 |
| Hardness |
Knoop(daN/mm2):
1800 parallel to C-axis, 2200 perpendicular to C-axis, Mohs: 9 |
| Optical
transmission range, µm |
0.17 - 5.5 |
| Refractive
index at 0.532 µm |
n0=1.7717,
ne=1.76355 |
| Water
absorption |
nil |
| Young
Modulus, Gpa |
345 |
| Shear
Modulus, Gpa |
145 |
| Bulk
Modulus, Gpa |
240 |
| Bending
Modulus (Modulus of Rupture), Mpa |
420 at 20°C,
280 at 500°C |
| Elastic
Coefficient |
C11=496,
C12=164, C13=115, C33=498, C44=148 |
| Poisson
ratio |
0.25-0.30 |
| Friction
Coefficient |
0.15 on steel,
0.10 on sapphire |
| Tensile
strength, MPa |
400 at 25°,
275 at 500°, 345 at 1000°
|
| Flexural
strength, daN/mm2 |
35 to 39
|
| Compressive
strength, GPa |
2.0
|
| Young’s
modulus E, daN/mm2 |
3.6 x 104
to 4.4 x 104
|
Specific
heat, J/(kg x K)
|
105 at 91°K,
761 at 291°K |
| Thermal
coefficient of linear expansion, K-1,at 323K |
6.66 x 10-6
parallel to optical axis, 5 x 10-6 perpendicular
to optical axis |
Thermal
conductivity, W/(m x K) at 300K
|
23.1 parallel
to optical axis, 25.2 perpendicular to optical axis |
| Resistivity,
Ohm x cm |
1016
(25°), 1011 (500°), 106 (1000°) |
| Dielectric
constant |
11.5 (103
- 109 Hz, 25°) parallel to C-axis, 9.3 (103
- 109 Hz, 25°) perpendicular to C-axis |
| Dielectric
strength, V/cm |
4 x 105 |
| Loss
tangent |
1 x 10-4 |
Solubility
-in water
-in HNO3,H2SO4, HCl,
HF
-in alcalis
-in melts of metals Mg, Al, Cr, Co, Ni, Na,
K, Bi, Zn, Cs |
insoluble
insoluble to 300°C
insoluble to 800°C
insoluble to 800-1000°C |
| g
-radiation stability |
No change
in transmission above 2.5 mm after exposure to 107
Rads. No visible coloration after exposure to 108 Rads/hr
for 60 minutes at - 195°C |
| Proton
radiation stability |
No change
in transmission below 0.3 µm after exposure to 1012
proton/cm2 total dose |
Chemical
resistance
|
Sapphire
is highly inert and resistant to attack in most process environments
including hydrofluoric acid and the fluorine plasma applications
commonly found in semiconductor wafer processing (NF3, CF4) |
We can deliver
the Sapphire material produced by each of the three different methods
of sapphire growth:
| Kyropolis
method |
The crystallization
process starts with the bait because of the minimal temperature
of the melt. The shape and size of the crystal depends on the
thermic field. In this method the melt level is being lowered
due to the difference in the crystal and melt concentration.
The growth speed is 0.15 kg/hour, the crystal diameter is 100
to 240 mm.
The process is highly automated.
Kyropolis method is used to produce a large boule of sapphire,
most typically of a cylindrical form. As-grown boule can be from
70 up to 200 mm in diameter and up to 250 mm in height. Sapphire
grown by this method normally has a very high optical quality,
and can be cut into wafers of any crystallographic orientation.
This method is applied for manufacturing substrates for blue LEDs
and SOS wafers. |
| Bagdasarov
method |
Crystals
are grown from the melt in a horizontal boat-shaped container.
This method makes it possible to get big and perfect single crystals.
Growth speed is 8-10 mm/hour, blank size is 320 x 115 x 30 mm.
Bagdasarov method produces sapphire in a slab form, making it
possible to get very thick windows and components. Typical crystals
grown by this method have a form of thick window (180mm x 150
mm x 25 mm). This material possesses high optical quality, and
is ideal for manufacturing sapphire windows of large diameters.
This material can be also used for producing wafers for blue LEDs. |
| Stepanov
method (EFG) |
Growth speed
is 1 to 4 cm/hour in Inert medium (argon).
The method makes it possible to grow crystals of complicated shape.
Blanks (ribbons) 80 mm thick and 300 mm long can be produced.
Stepanov (or EFG) method - a shaped growth technique used for
growing sapphire in near-net finished shape, including tubes,
rods, sheets, and fibers. This technique can also provide unique
shapes and sealed assemblies. By Stepanov method, ribbon crystals
up to 500 mm long and 80 mm wide are grown. Crystals grown by
this method can have different crystallographic orientations (A,
R, random) and are mainly used for industrial & mechanical
applications, where good optical qualities are not important.
|
Typical Sapphire applications:
Sapphire
substrates:
· Blue LED's (BLED's) - sapphire is the substrate for the growth
of III-V and II-VI compounds such as GaN for LED's,
· for IR Detectors, for the growth of mercury cadmium tellurium
(HgCdTe), GaAs wafer carriers, microwave integrated circuits
Aerospace:
· Sapphire is used for its durability and erosion/corrosion
resistance, often in combination with the ability to withstand high
heat while having a very broad transmission range. Applications
include:
· Windows - FLIR (Forward Looking Infra Red) windows for sensors
and other optics. Optical clarity over a broad spectral range combines
with durability in this application.
· Windows - for erosion resistance in salt and blowing sand
environments, sapphire is used in conventional windows and dome shapes
in replacement of softer, more fragile IR transmitting materials.
· Countermeasures lamps - sapphire flash lamps are used in
IRCM's (Infra red countermeasures). The high temperature performance
of sapphire is combined with broad spectral range in this application.
Analytical applications:
· Sapphire is used in analytical applications where combinations
of high temperature, pressure, and hydrofluoric acid species are encountered.
These applications need the survivability of sapphire, while often
needing other properties such as favourable UV (ultraviolet) or IR
(infrared) transmission.
· NMR (Nuclear Magnetic Resonance) tubes; Sapphire is used
for very high-pressure applications in replacement of glass or quartz
tubes.
· Sample preparation - sapphire is used in digestion cells
as sheaths and liners. When hydrofluoric acid is used, sapphire replaces
quartz components
· Analytical chemistry - for mass spectroscopy, ICAP, and other
systems, sapphire replaces quartware to improve durability and reduce
contamination while offering good UV transmission.
Medical applications:
· Sapphire is used in surgical systems for laser transmission
and in contact with bodily fluids.
· Surgical tips - sapphire is used in contact tips for various
surgical laser applications
· Endoscope lenses - sapphire is often used in endoscope lenses
due to its durability in contact with tissues and in sterilisation
environments such as autoclaving
· Sapphire knives - with a sapphire knife, thinner sections
are possible. The near perfect cutting edge of this knife / blade
gives distortion-free sections down to 10 microns thick.
Optical applications:
· Sapphire is used for short and long wavelength applications
(UV and IR) beyond the range where conventional optics performs adequately.
High temperatures and hostile environments also necessitate the use
of sapphire optics.
· Illumination windows - for very high brightness illumination,
sapphire windows survive the very high heat while providing the broadest
spectral transmission.
· Sapphire lightguides - sapphire rods; used in high temperature
thermometry beyond the range of quartz optics.
· Optical components: lenses, prisms and other laser and infrared
optics are fabricated from high optical quality sapphire.
Watch
industry: Sapphire is widely used for watch glasses. The world
demand in watch industry centres on scratchproof sapphire watch crystals.
However, besides traditional flat shapes, crystals with spherical
and cylindrical curves are also in great demand.
Typical specifications:
|
Available
orientations:
|
C-axis
[0001], R-axis [1-102], A-axis [11-20], M-axis [10-10], Random |
|
Sapphire
windows / blanks
|
|
|
Diameter
/ Width:
|
25.0 - 250.0
mm
|
|
Tolerance:
|
Standard
± 2°, Special to ± 0.1°
|
|
Thickness:
|
Minimum
0.15, maximum 120.0 mm
|
|
Surface
finish:
|
As cut,
fine ground, lapped, polished s/d 80/50, 60/40, 40/20, 20/10,
10/5, according to the MIL-0-13830A
|
|
Ends / Edge
quality:
|
Fine ground,
80/50
|
| "As-grown"
sapphire tubes: |
|
| Dimensions |
Up
to 50 mm inner diameter, 0,5 - 4,0 mm wall thickness, 300-600
mm tubes length |
| Orientation |
C-axis
in the length of the tube |
| Polished
sapphire tubes: |
Up
to 50 mm inside diameter, 0,5 - 3,0 mm wall thickness, 80-350
mm tubes length |
|
Ingots: |
Diameter/Width
5-220 mm, Thickness/Length 25 – 125 mm |
| Surface
quality |
As-cut,
Ends/Edge Quality Diamond cut |
Sapphire quality grades:
- Grade 1:
free of insertions, block boundaries, twins, microbubbles and scattering
centers;
- Grade 2:
free of insertions, block boundaries, twins; individual scattering
centers (microbubbles < 10 µm located not closer than 10 mm)
are allowed;
- Grade 3:
free of insertions, block boundaries, twins; individual bubbles
< 20 µm located not closer than 10 mm to each other are allowed;
- Grade 4:
free of insertions, block boundaries, twins; bubbles < 20 µm
located not closer than 2 mm from one another as well as bubbles
clusters (which may include individual bubbles to 50 µm) of
size < 200 µm scattered not closer than 10 mm to each other
within the effective volume 20x20x20 mm are allowed;
- Grade 5:
free of insertions, block boundaries, twins; bubbles < 20 µm
located not closer than 2 mm from one another as well as bubbles
clusters (which may include individual bubbles to 50 µm) of
size < 500 µm scattered not closer than 5 mm to each other
within the effective volume 20x20x20 mm are allowed;
- Grade 6:
free of insertions, block boundaries, twins; defective areas with
bubbles clusters of size > 500 µm are allowed.
We consider grades
1-4 as optical ones; 5-6 as technical ones. For all optical grades,
blue and green coloration is not allowed. For all technical grades,
coloration is not controlled. Insertions, block boundaries and twins
inside the material are controlled visually between crossed polarizers. |