The 1.7 kg Microchip Eric Williams, United Nations University Robert U. Ayres, INSEAD Miriam Heller, NSF Motivations Growth of IT industry: macro-economic scale and continued high growth (average annual growth of global semiconductor industry is 16% per year in recent decades) .
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Eric Williams, United Nations University
Robert U. Ayres, INSEAD
Miriam Heller, NSF
Growth of IT industry: macro-economic scale and continued high growth (average annual growth of global semiconductor industry is 16% per year in recent decades) .
What are the environmental implications of this new industry? Are there general trends in relationship between high-tech economy and materials use/environment?
Only use publicly available sources, fully report all data and assumptions used.
2. Quartz to Silicon wafers
3. Semiconductor-grade chemicals
Aggregate chemical input/emission
Various sources suggest 1.4-1.6 kWh of electricity consumed per cm2 of wafer processed, 80-90% of total energy use is electricity. Data reflects aggregate of national industries.
Data sources: Census, JEIDA, Semiconductor Industry Association, Microelectronics and Computer Technology Corporation (MCC)
Take “typical” figure as 20 liters/cm2
Electenergy input/kg silicon
Quartz + carbon → silicon
Harben, 99; Dosaj, 97
Silicon → trichlorosilane
O’Mara et al, 90
Trichlorosilane → polysilicon
Tsuo et.al, 98; O’Mara, 90;Takegoshi, 94
single crystal ingot
Single crystal ingot → silicon wafer
Lammers and Hara, 96
Process chain to produce wafer
9.5%From quartz to wafers
Production of silicon wafers requires around 160 times
The energy required for “industrial” grade silicon
Energy use: .34 kWh per cm2 of input silicon.
Material inputs: packaging material (epoxy, ceramic), lead frame (copper, aluminum), processing chemicals.
Data sources: MCC, JEIDA
Combine previous process data with information on wafer yields for 32MB DRAM chips (Semiconductor International, 1998): 1.6 cm2 of input wafer per chip.
Breakdown of life cycle energy use in production
and use of 1 2-gram memory chip
For 1 memory chip, lower bounds are:
Total fossil fuel and chemical use to produce 2 gram memory chip 1.7 kg
Measure material and energy intensity: secondary materialization index (SMI):
Secondary materials counted are only those obviously “destructively consumed”: fossil fuels and chemicals (water and elemental gases not included).
SMI index for various products:
Despite trivial physical weight, “secondary” weight of chips is substantial.
Why such a dramatic figure?
Postulate: Because chips are exceedingly highly organized (low entropy) objects, the materials and energy required for processing is especially high.
Estimate order of magnitude of entropy changes associated with final product and producing high-grade inputs:
Entropy (at room temp) = 9.5x10-20 J per memory chip
Entropy change (at room temp) = 17 J/kg of pure water
Magnitudes of entropy change much lower than energy use - does not explain practical experience of high energy needed for pure materials.
Third law of thermodynamics (Nernst, 1906): it is impossible to reach absolute zero in a finite number of reversible steps
Analogous phenomenon for purity? Conjecture: energy efficiency of purification decreases as one approaches perfect purity.
It follows that all purification processes have efficiency <1 and achieving higher purity with given process requires increasing # of steps (e.g. .9 x .9 x .9 ….)
Many advanced materials/products are also low entropy. Does their proliferation imply increase in SMI of overall economy?
The possibility of this is called secondary materialization
Not known if significant, but suggests importance of life cycle materials studies to clarify. Need to carefully treat chemicals industry and purification/materials processing.
Analysis of energy use in production of desktop computer with 17-inch CRT monitor
Hybrid method that splits estimation into process and economic IO pieces.
For desktop, production phase is 83% of total life cycle energy, very high share compared to other appliances such as refrigerator, which has 12% in production phase.
Combination of high energy intensity in production and short lifespan imply that lifespan extension is key approach that should be pursued in policy for managing impacts of IT equipment.