Microtechnology/Materials

Overview

Overview of the electronic structure of the different fundamental classes of materials. Atoms have discrete energy levels for each electronic state. Electronic transitions by eg. optical excitation can change the state of the atom. Molecules can also have discrete energy levels, but the more complex structure also gives a much more complex diagram of electronic states. In addition, the molecules can rotate and vibrate which modulates the observed energy levels. Insulators can be seen as a condensed phase of molecules with little electronic connection between neighboring molecules for conducting a current. Only when excitation is made with an energy above the several eV bandgap will conduction be possible. Semiconductors have a more narrow bandgap and even at room temperature a few conduction electrons will be excited into the conductance band. Doped Semiconductors have higher electrical conductance because added dopants provide conduction electrons. Metals can be considered as ionized metal atoms in a sea of free electrons, giving a high conductivity and high reflectivity of light (as long as it is not too high in frequency)

Resources with overviews of materials and their most prominent uses:

• Semiconductor materials
• Ioffe NSM data archive
• overview of microfabrication materials
• overview of microfabrication materials
• Semiconductor materials
• polymers

Overview table of microfabrication materials

Microfabrication Materials Overview Table

Material	Typical use	Density [g/cm3]	Atm. Mass[g/mol]	Youngs Modulus[GPa]	Shear modulus [GPa]	El. Conductivity	Therm. Cond.[W·m−1·K−1]	Melting point[K]	Notes
Aluminium	Leads	2.70	26.98	70	26	26.50 nΩ·m	237	933.47 K (660.32 °C)	Add notes
Gallium Arsenide	Light emitter	5.3176	144.645	youngs	bulk	el.	therm.	1238°C (1511 K)	Bandgap 1.424 eV
Gallium Nitride	Blue Light emitter	6.1	83.7297	youngs	bulk	el.	therm.	K ( °C)	Add notes
Polysilicon	solar cells	den	amu	youngs	bulk	el.	therm.	K ( °C)	highly dependent on doping and annealing. Se detailed table in the silicon section
Silicon	Wafers, semiconductor	2.33	28.0855(3)	47	bulk	el.	149	1687 K (1414 °C)	highly dependent on doping. Se detailed table in the silicon section
Silicon dioxide, silica	insulator, light waveguide	den	amu	youngs	bulk	el.	therm.	K ( °C)	Add notes
Silicon nitride	insulator	den	amu	youngs	bulk	el.	therm.	K ( °C)	Add notes
Gold	Coating of leads	19.3	196.966569	78	220	22.14 nΩ·m	318	1337.33 K (1064.18 °C)	Add notes
Nickel	MEMS, leads	den	amu	youngs	bulk	el.	therm.	K ( °C)	Add notes
Platinum	Contact pads	den	amu	youngs	bulk	el.	therm.	K ( °C)	Add notes
PMMA	1.19	50.000-950.000	youngs	bulk	el.	therm.	378 K (105°C) glass trans.	Refractive index 1.492
SU8 polymer	den	amu	youngs	bulk	el.	therm.	K ( °C)	Add notes
Tungsten	den	amu	youngs	bulk	el.	therm.	K ( °C)	Add notes

This table should be merged with the above...

Metal Material Properties

		Mechanical				Thermal			Electrical
		Yield Str.	Youngs.	Pois.	Density	Th. Cond.	Th. Exp.	Melting	El. cond.	α
Highest Z	Material	GPa	GPa	?	kg/m³	(W/cmK)	(ppm/K)	K	Ωm	promille/K
Metals
34	Al	0.17	70	0.34	2698	2.36	23	660	26.5*10??	4.3
55	Au	?	78-80	0.44-0.25	19281	3.12	14	1064	23-22.1*10??	3.7
66	Cr	?	?	?	7194	?	?	1860	?
55	Ti	0.23	116	0.32	4508	0.2	8.5	1670	420*10??	3.8
80	Pt	0.12	168	0.38	21450	0.73	8.9	1772	0.0981?	3.9
78	W	0.12	411	0.28	19254	1.8	4.5	3387	0.0489?	4.8
65	Ag	?	?	?	?	?	?	960	15.9*10??
56	Fe	12.6	196	0.29	7873	0.803	11.7-12	1540	89E	6.6
Semimetals
12	Graphite	?	?	?	2266	?	?	3700	7-60E	-0.4
Semiconductors
25	Si intrinsic	7	190	?	2329	1.57	2.33	1410	2.5*10³
25	poly Si	?	150-170	0.3-0.066	2320	0.5-0.34	2.6	?	22000
25	SiC	21	700	?	3200	3.5	3.3	?	?
45	InP	?	7.1E11 dyn cm-2	?	4810	0.68 W cm-1 °C-1	4.60·10-6 °C-1	1060	?
Insulators
12	Diamond	53	1035	?	3500	20	1	?	2.7
34	Al2O3	15.4	530	?	4000	0.5	5.4	?	?
25	SiO2 (bulk)	8.4	73	?	25-2150	0.014	0.55	?	E-12

Units

• 1 g/cm3 = 1 kg/L = 1000 kg/m3
• g/mol = amu = Da

Applications and Uses

• Microprocessors
• Transistors
• Lab-on-a-chip
• MEMS

Product Life-Cycles

Cheap and disposable point-of-care microfluidic chips require very different materials compared to high performance microprocessors.

Environmental Considerations

The environmental footprint of microfabriaction is not discussed very often. If anyone has knowledge about this I hope they will contribute!!

Wafers and Substrates

Overview of wafer types, flats, cleaving planes etc.

References

See also notes on editing this book about how to add references Microtechnology/About#How to Contribute.