MPXM2053GS datasheet(28/670 Pages) MOTOROLA

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Motorola Sensor Device Data

www.motorola.com/semiconductors

Figure 5. Experimental results for the etching of (100)

silicon with approximately 5x10–5 cm–3 boron

doping density in a commercially available detergent

as a function of temperature and detergent

concentration (which is proportional to pH).

Etch Rate

<= 0.10

<= 0.20

<= 0.30

Prediction

<= 0.40

> 0.40

from Model

100

110

120

Contour Plot of Detergent Concentraion and

Temperature vs Etch Rate ( m/hr)

ULTRA TIDE CONC (g/l)

Polymer Swelling or Dissolution

Swelling or dissolution affects those polymers typically

employed to package the micromachined structure and

depending on the nature of the media, may have a degrading

effect on device performance. These two related phenomena

are caused by solvent diffusing into the material and

occupying free volume within the polymer. The solubility

parameter gives a quantitative measure of the potential for

swelling [21]: i.e., it provides a quantitative measure of “like

dissolves like” (Fig. 6). Both the polymer and the solution

contribute to this failure mechanism, while the media

(specifically, the solubility parameter), the temperature, and

the pressure can be used as acceleration factors.

Figure 6. Typical values of solubility parameter

(

δ [cal/cm3]1/2) for solvents and polymers.

ISOOCTANE

TOLUENE

ETHANOL

METHANOL

WATER

22.5

17.5

12.5

7.5

Solvents

POLYSULFONE

POLYURETHANE

PET

NYLON

POLY (ACRYLONITRILE)

Polymers

PTFE

PMMA

δ = [cal/cm3]1/2

Figure 7 shows a photograph of a device after exposure to

a harsh fuel containing corrosive water solution. This

corrosion and evidence of swelling of the gel demonstrates the

vital importance the package has on the reliability of the

pressure sensor device. Also, it has been observed that

corrosion occurs more readily following swelling of a

polymeric encapsulant.

Figure 7. Photograph of a pressure sensor device

after extended exposure to harsh fuel containing

corrosive water, followed by exposure to a strong

acid. Evidence of the gel swelling during the test,

and corresponding shrinkage after removal from the

test media can be seen by the gel retracting away

from the sidewall of the package.

INITIAL EDGE

OF GEL

GEL EDGE

AFTER EXPOSURE

TO GASOLINE

WITH ETHANOL

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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