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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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the 1 7 kg microchip

The 1.7 kg Microchip

Eric Williams, United Nations University

Robert U. Ayres, INSEAD

Miriam Heller, NSF

motivations
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) .

What are the environmental implications of this new industry? Are there general trends in relationship between high-tech economy and materials use/environment?

life cycle inventory of microchip
Life cycle inventory of microchip
  • Estimate life cycle inventory of energy and aggregate chemical use for production of common microchip.
  • Energy use is good indicator of impacts on climate change and fossil fuel use. Aggregate chemical use is poor indicator of impacts on local soil, air, water systems.
guiding principles
Guiding principles

Only use publicly available sources, fully report all data and assumptions used.

  • Critically compare different data sources for different processes.
  • Compare final results with those from other groups and deconstruct differences.
key processes
Key Processes

1.Wafer Fabrication

2. Quartz to Silicon wafers

3. Semiconductor-grade chemicals

4. Assembly

chemical input compare data sources
Chemical input :Compare data sources

1

Aggregate chemical input/emission

energy use in fabrication
Energy use in fabrication

1

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)

water use in fabrication
Water use in fabrication

1

Take “typical” figure as 20 liters/cm2

f rom quartz to wafers

Stage

Electenergy input/kg silicon

Silicon

Yield

Data sources

Quartz + carbon → silicon

13 kWh

90%

Harben, 99; Dosaj, 97

Jackson, 96

Silicon → trichlorosilane

50 kWh

90%

Takegoshi, 94;

O’Mara et al, 90

Trichlorosilane → polysilicon

250 kWh

42%

Tsuo et.al, 98; O’Mara, 90;Takegoshi, 94

Polysilicon →

single crystal ingot

250 kWh

50%

Takegoshi, 94

Single crystal ingot → silicon wafer

240 kWh

56%

Takegoshi, 94;

Lammers and Hara, 96

Process chain to produce wafer

2,130 kWh

9.5%

From quartz to wafers

2

Production of silicon wafers requires around 160 times

The energy required for “industrial” grade silicon

c hemical inputs to fabrication
Chemical inputs to fabrication

3

  • Semiconductor grade chemicals/gases typically 99.999-99.9999% purity, requires substantial purification, for which no data was available.
  • Data used reflects production of industrial grade chemicals (used Boustead database, other LCA databases same).
  • Distillation processes are, in general, energy intensive.
assembly
Assembly

4

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

lca of 32mb dram chip
LCA of 32MB DRAM chip

Combine previous process data with information on wafer yields for 32MB DRAM chips (Semiconductor International, 1998): 1.6 cm2 of input wafer per chip.

e nergy use for different stages in life cycle of 32 mb dram chip
Energy use for different stages in life cycle of 32 MB DRAM chip

Breakdown of life cycle energy use in production

and use of 1 2-gram memory chip

fossil fuel chemical and water use
Fossil fuel, chemical, and water use

For 1 memory chip, lower bounds are:

  • Fossil fuels consumed in production = 1,200 grams
  • Fossil fuels consumed in use = 440 grams
  • Chemicals “destructively” consumed = 72 grams
  • Water use is 36,000 grams per chip.

Total fossil fuel and chemical use to produce 2 gram memory chip  1.7 kg

secondary materialization
Secondary materialization

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:

Microchip: 640

Automobile: 1-2

Refrigerator: 2

why so different
Why so different?

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.

entropy analysis
Entropy analysis

Estimate order of magnitude of entropy changes associated with final product and producing high-grade inputs:

  • Mesoscopic order of microchip: use S=-k ln W and checkerboard model. Cell length = 1 μm Board length = die size = 1 cm. result:

Entropy (at room temp) = 9.5x10-20 J per memory chip

  • Ultra-high purity water (tap water – 100 ppm impurities, fab water - 1 ppb). Use entropy of mixing: ΔS= -R [(1-x) ln (1-x) + x ln x ] (x = impurity concentration) result

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 for purity as well as temperature
Third law of thermodynamics for purity as well as temperature?

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.

Conjecture:

  • 100% purity is impossible (no perfect vacuum)

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 ….)

secondary materialization22
Secondary materialization

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.

hybrid lci for desktop computer
Hybrid LCI for desktop computer

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.

c ommentary
Commentary

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.

slide26
Thank

You

Eric Williams

Williams@hq.unu.edu