4 Poly Etch Rate Variation

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• (4) Poly Etch Rate Variation
• Wider spacing between Poly fingers ? faster etch
  rate.

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• Multi strip Poly resistors ? strips on the ends
  need Dummy strips

3

• Closed-loop Dummies ? problem due
  to inductive interaction with EM fileds.
• Either break them up (fig.7.7) or at least have a
  gap to stop current path.

• Dummies need electrical contact to the Tank.

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• (5) Diffusion interactions
• Consider diffused-base resistors (fig.7.8)
• Diffused resistors usually are laid in a Tank
  with NBL.

• Edges of diffused areas have diffusion tails. ?
  resistors occupying the ends slightly
  different values. ? use dummy resistors
  (fig.7.8)

5

• Layouts designs for serpentine resistors
  (fig.7.9)
• Layouts in Tanks with deep-N sinkers (fig.7.9)

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• (6) Stress Gradients and Package Shifts
• Packaging can exert stress onto Die.
• Metal Can package, Ceramic package, and Plastic
  package

Metal Can package
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Ceramic package, and Plastic package
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• Metal Can package or Ceramic package ? lowest
  stress
• Use metal header plate, mounted using Epoxy.
• Solder or gold eutectic mounting ? higher stress

• Plastic package ? higher stress
• Epoxy resin for mounting
• Residual stress due to difference in CTE of Si
  and Epoxy
• Shifts in Offset voltage in OpAmp, Comparators,
  or output ref. Voltage ? Package shifts

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Coefficients of Thermal Expansion (CTE)
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• Piezoresistivity
• N-type (100) Si
• Maximum piezoresistivity along lt100gt
• Minimum along lt110gt gtN-type diffused resistors
  along lt110gt

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• P-type (100) Si
• Maximum along lt110gt
• Minimum along lt100gt
• P-type diffused resistors along lt100gt

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• (111) Si ? isotropic

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• Gradients and Centroids
• Stress distribution on a Die surface isobaric
  contour plot

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• Place matched devices at Regions of lowest
  stress gradients.

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• Place matched devices at Regions of lowest
  stress gradients.

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• Matched devices must reside as close as possible
  ? minimize the stress
  difference
• Centroid of the device center of stress
  distribution

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• Common-Centroid Layout
• Example
• Two matched devices, A and B.
• Each device consists of two sections.

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• Segmenting devices
• 1. Finding the greatest common factor
• Example 10kW and 25 kW ? 5kW segment size
• 2.Use the smaller device as basic segment
  remainder should be gt 70
• Example 39.7kW and 144.3 kW ?
• Case-1 Use 39.7kW as a single segment. ?
  144.3/39.7 3.637 (3 segments 25.2kW 64)
• Case-2 Divide 39.7kW into two segments ?
  unit 39.7 19.85kW ? 39,7kW 2 segments
  144.3 144.3/7.27 7 segments
  27 of unit.
• Case-3 Divide 39.7kW into 3 segments ? unit
  39.7/3 13.233kW ? 39.7kW 3 segments
  144.3kW 144.3/13.233 10.904 10 segments
  90 (11.97kW).
• 3.Do not use too small a segment.
• 4.Make partial R segment using a sliding contact.
• 5.Capacitor segments should not have dimensions
  much less than 100 mm2.

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• Coincidence, Symmetry, Dispersion, and
  Compactness

1-dimensional
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• Coincidence, Symmetry, Dispersion, and
  Compactness

2-Dimensional

• Cross-coupled pair

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• Coincidence, Symmetry, Dispersion, and
  Compactness

2-Dimensional

• Cross-coupled pair
• Tiling

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• (7) Temperature and Thermoelectric Effect
• DIP or SOIC Tj Ta Pd qja
• Tj Junction temperature
• Ta ambient temperature
• Pd power dissipated in package
• qja junction-to-ambient thermal impedance
• 16-pin DIP qja 110 C/W
• 16-pin surface-mount (SOIC) qja 131 C/W

• Power package Tj Tc Pdqjc
• Tc case temperature
• qja junction-to-case thermal impedance.
• 3-lead plastic TO-220 Power Package qja 4.2
  C/W
• 3-lead metal TO-3 can power package qja 2.7

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• Thermoelectric effect ET S DTc
• S Seeback coefficient ( 0.4mV/C)
• DTc temperature difference between two contacts
  of the resistor
• Example 0.4mV offset in Bipolar mirror produces
  1.5 mismatch in the currents.

Power device
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