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| '''Volunteer Opportunities''' <<BR>>(1) Look for compounds and composite materials that closely match silicon.<<BR>>(2) Find properties for isotopically pure silicon; it allegedly has 60% better thermal conductivity, it gets much better at lower temperatures, and it is getting cheap enough to use in chips. It may be the best material for heat spreaders }}} | '''Volunteer Opportunities''' <<BR>>(1) Look for compounds and composite materials that closely match silicon. |
Manufacturing Server Sky
Devices and materials
A lot can be done on a very thin planar surface. Other things cannot be done easily. Here are some common electronic devices:
Thin Planar |
Non-planar |
Printed circuit laminates (ultrathin) |
Connectors |
Resistors |
cooling fins |
Planar Capacitors |
Wound foil capacitors |
pixel sensor arrays |
lenses |
liquid crystal light modulators |
LEDs (?) |
Striplines |
Coax |
Microwave-frequency inductors |
Low frequency inductors and transformers |
surface acoustic wave (SAW) resonators |
crystals |
beam lead interconnect |
wirebonds and solderbumps |
Silicon is the construction material of choice - the solar cell is made of silicon, and the processors and memory are also. Here are some relevant properties of silicon, SiO2 glass, gallium arsenide, copper, aluminum, silver, gold, tantalum, indium tin oxide, kovar, invar, alumina, and pyrolytic graphite, which will make up 99.9% of the weight of a server-sat:
property |
Si |
SiO2 |
Si3N4 |
GaAs |
Cu |
Al |
Ag |
Au |
Ta |
ITO |
Kovar |
Invar |
Al2O3 |
PyroC |
Density g/cm^3 |
2.33 |
2.65 |
3.20 |
5.32 |
8.96 |
2.7 |
10.5 |
19.3 |
16.7 |
6.43 |
7.85 |
8.05 |
3.96 |
2.25 |
Coeff. of Thermal Expansion 10-6/K |
2.6 |
0.5 |
3.2 |
5.7 |
16.5 |
23.1 |
18.9 |
14.2 |
6.3 |
10? |
5.3 |
1.3 |
5.5 |
4.3 |
Heat Capacity J/g-K |
0.71 |
0.74 |
0.71 |
0.33 |
0.38 |
0.90 |
0.24 |
0.13 |
0.14 |
- |
0.44 |
0.51 |
0.75 |
0.72 |
Heat Capacity MJ/m3-K |
1.65 |
1.96 |
2.27 |
1.76 |
3.40 |
2.43 |
2.47 |
2.49 |
2.34 |
- |
3.45 |
4.11 |
2.97 |
1.62 |
Thermal Conductivity W/m-K |
149 |
1 |
30 |
55 |
401 |
237 |
430 |
320 |
58 |
- |
17.3 |
10.1 |
46 |
1950 |
Specific thermal conductivity |
64 |
0.4 |
9.4 |
10 |
45 |
88 |
41 |
16 |
3.5 |
- |
2.5 |
12 |
11.6 |
870 |
Thermal Diffusivity mm2/s |
90 |
0.5 |
13 |
31 |
118 |
98 |
174 |
129 |
25 |
- |
5 |
2.5 |
3.9 |
540 |
Youngs Modulus GPa |
150 |
73 |
260 |
86 |
110 |
70 |
83 |
78 |
186 |
116 |
140 |
148 |
370 |
4.8 |
speed of sound km/s |
8.0 |
5.2 |
9.0 |
4.0 |
3.5 |
5.1 |
2.8 |
2.0 |
3.3 |
4.2 |
4.2 |
4.3 |
9.7 |
1.5 |
Tensile Strength MPa |
7000 |
50 |
70 |
57 |
210 |
40 |
170 |
100 |
200 |
120 |
270 |
680 |
300 |
- |
Atomic Weight (avg/atom) |
28 |
20 |
20 |
72 |
64 |
27 |
108 |
197 |
181 |
57 |
57 |
56 |
20 |
6 |
Resistivity nano-ohm-m |
- |
- |
- |
- |
17 |
27 |
16 |
22 |
131 |
2200 |
490 |
820 |
- |
14000 |
Dielectric Constant |
11.8 |
3.9 |
7.5 |
12.9 |
- |
- |
- |
- |
- |
- |
- |
- |
9.9 |
- |
Data mostly from wikipedia and various places online. See also Matweb the material properties website, B.Y.U. CTE table. Tensile strength untrustworthy, and many parameters are anisotropic. Use only for rough estimates.
The vast bulk of the material , and the largest pieces of of the server-sat, will be silicon. Since the server-sat undergoes wide temperature changes when it passes in and out of shadow, or undegoes thermal annealing, it will be more survivable if the non-silicon portions are made of composite materials that match silicon's 2.6E-6/Kelvin coefficient of thermal expansion (CTE). For example, Zicar Ceramics SALI-2 (search on Matweb]] is a mixture of 80% alumina, 20% silica with a a CTE of 6.2E-6 . Alumina, combined in different proportions with silica ( SiO2 ) , might be nicely matched to silicon.
Server sats will also need transparent materials and conductors that closely match silicon. The metals have very high CTEs, while SiO2 has a very low CTE, so slotted metal wires with SiO2 in the gaps is one way to make a "material" that is both conductive and has the same CTE as silicon.