Mechanical Properties

Mechanical Properties

In the first of the two chapters on mechanical properties the emphasis is the develop- 

ment of the basic ideas and the resulting relationships among the elastic constants. In 

Chapter 7 on the elasticity property of solids, these constants are used to describe the 

behavior of materials that deform elastically,which means that as forces are applied,the 

material deforms, but the material returns to its original state as the forces are removed. 

Most materials exhibit this behavior when small forces are applied for short periods of 

time. There is more interest when larger forces are applied that leave a material perma- 

nently deformed or even causes fracture of the material, since deformation and failure 

relate the usefulness of a material for fabricating products such as cars, bridges, and 

homes. However, as was the case for structure, first the simpler ideal case of elasticity is 

considered and then consideration is given to a more complicated behavior called plas- 

ticity.In Chapter 8 on the plasticity property of solids the underlying ideas are presented 

for permanent deformation or plasticity. The implication of dislocations for the plastic 

deformation of crystalline materials is discussed and creep is briefly discussed. In this 

chapter the deformation of noncrystalline materials such as polymers is discussed, and 

several models that are used to interpret the mechanical response ofthese kinds ofmate- 

rials are developed. 

In microelectronics and photonics many of the devices are constructed by layering 

films of dissimilar materials.Therefore differences in thermal expansion as well as chem- 

ical incompatibilities at the interfaces can lead to performance and reliability issues for 

the devices. Furthermore many of the extreme structural features and extremely small 

sizes of features of the modern devices can exacerbate the mechanical issues that may 

exist for planar and larger devices. In addition the applications of forces on a crystal 

lattice can alter the atomic spacing and therefore affect the electronic nature, meaning 

the electronic energy band structure, of a material. A full analysis of these complicated 

structural and electronic issues is beyond the scope of this text, but a first-order treat- 

ment of the important relationships properties is essential so that advanced study and 

appreciation of the implications of mechanical properties can be accomplished. 

Many modern microelectronics products such as computer chips are fabricated from 

thin films of dissimilar materials.Also,once the layered structures are formed,the prod- 

ucts go through various temperature cycles as part ofthe further processing.These struc- 

tures are prone to the development of stresses that can lead to device failure and to 

shorter useful lifetimes. Consequently the mechanical issues of thermal expansion, 

stresses,and defect formation that are crucial to further study of electronic material reli- 

ability are covered in these two chapters.

Ramon A. Carmona C

C.I 17646653

CRF

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