Buffered quartz crystal

Claim 2

A piezoelectric crystal for measurement of the deposition of a film of material, including a crystal layer having front and back surfaces, a back electrode deposited on the back surface of the crystal layer, and a front metallic electrode deposited on the front surface of the crystal layer and upon which said film of material accumulates during a deposition process to change the natural oscillation frequency of the crystal, wherein said front electrode includes an adhesion layer deposited against the front surface of the crystal layer, a compliant buffer layer deposited on the adhesion layer, and a conductive metallic electrode layer formed of gold or silver deposited on the buffer layer; said buffer layer being formed of an element having the following properties: a suitably low bulk modulus and a suitably low Young's modulus; the layer being of a suitable thickness to absorb strain between the electrode layer and the film of material being deposited thereon; a good adhesion for the gold or silver of the conductive electrode layer; a suitably high thermal conductivity; and a low acoustic damping characteristic to avoid undue damping of vibrations in the crystal; so as to prevent interfacial stresses during the deposition process from causing early catastrophic crystal failure, and thus to prolong the useful life of the piezoelectric crystal when used as a crystal microbalance in a film deposition process.

Claim 3

A piezoelectric crystal for measurement of the deposition of a film of material including a crystal layer having front and back surfaces, a back electrode deposited on the back surface of the crystal layer, and a front metallic electrode deposited on the front surface of the crystal layer and upon which said film of material accumulates during a deposition process to change the natural oscillation frequency of the crystal, wherein said front electrode includes an adhesion layer deposited against the front surface of the crystal layer, a compliant buffer layer deposited on the adhesion layer, and a conductive metallic electrode layer deposited on the buffer layer; said buffer layer having a suitably low bulk modulus and being of suitable thickness to absorb strain between the electrode layer and the film of material deposited thereon without undue acoustical damping of vibrations in the crystal, so as to prevent interfacial stresses during the deposition process from causing early catastrophic crystal failure, and thus to prolong the useful life of the piezoelectric crystal when used as a crystal microbalance in a film deposition process; wherein said buffer layer is selected from the group consisting of aluminum, bismuth, calcium, indium, lead, selenium, silver, tellurium, tin, cadmium and zinc.

Claim 4

A piezoelectric crystal for measurement of the deposition of a film of material including a crystal layer having front and back surfaces, a back electrode deposited on the back surface of the crystal layer, and a front metallic electrode deposited on the front surface of the crystal layer and upon which said film of material accumulates during a deposition process to change the natural oscillation frequency of the crystal, wherein said front electrode includes an adhesion layer deposited against the front surface of the crystal layer, a compliant buffer layer deposited on the adhesion layer, and a conductive metallic electrode layer deposited on the buffer layer; said buffer layer having a suitably low bulk modulus and being of suitable thickness to absorb strain between the electrode layer and the film of material deposited thereon without undue acoustical damping of vibrations in the crystal, so as to prevent interfacial stresses during the deposition process from causing early catastrophic crystal failure, and thus to prolong the useful life of the piezoelectric crystal when used as a crystal microbalance in a film deposition process; wherein said buffer layer is selected from the group consisting of aluminum, bismuth, calcium, indium, lead, selenium, silver, tellurium, tin, cadmium and zinc.

Claim 5

The piezoelectric crystal of claim 2, wherein said buffer layer is selected from the group consisting of zinc, cadmium, lead, copper, calcium and alloys thereof.

Claim 6

The piezoelectric crystal of claim 2 wherein said buffer layer is zinc.

Claim 7

The piezoelectric crystal of claim 2 wherein said adhesion layer is selected from the group consisting of titanium and chromium.

Claim 8

The piezoelectric crystal of claim 2 wherein said adhesion layer is a deposit of titanium or chromium about 100 to 160 Å thick; said buffer layer is a deposit of zinc about 6000 Å thick; and said electrode layer is a deposit of silver about 2000 Å thick.

Claim 9

The piezoelectric crystal of claim 2 wherein said crystal layer is an AT-cut quartz crystal.

Claim 10

The piezoelectric crystal of claim 7 wherein said crystal layer front surface has a suitable surface roughness with a mean deviation from true flatness of between about 15 to 25 microinches.

Claim 11

The piezoelectric crystal of claim 2 wherein said crystal natural oscillation frequency is from about four to about six megahertz.

Claim 12

A piezoelectric crystal for measurement of the deposition of a film of material, comprising a crystal layer of a piezoelectric crystal material having a front surface and a back surface, a back electrode deposited on the back surface of the crystal layer and a front metallic electrode including a layer of gold or silver deposited on the front surface of the crystal layer and upon which said film of material accumulates during a deposition process to change the natural oscillation frequency of the crystal, wherein said front surface of the crystal layer is provided with a surface roughness characterized by a mean deviation from true flatness on the order of about 15 to 25 microinches, and said front electrode includes a buffer layer of a conductive metallic material having the following properties: a suitably low bulk modulus and a suitable Young's modulus; said buffer layer being of sufficient thickness so that the buffer layer absorbs strain between the metallic electrode and the film of material being deposited thereon; a good adhesion for the gold or silver of the conductive electrode layer; a suitably high thermal conductivity; and a low acoustic damping characteristic to prevent undue damping of vibrations in the crystal; so as to prevent interfacial stresses during the deposition process from causing early catastrophic failure, and thus to prolong the useful life of the piezoelectric crystal when used as a crystal microbalance in a film deposition process.

Claim 13

A piezoelectric crystal for measurement of the deposition of a film of material, comprising a crystal layer of a piezoelectric crystal material having a front surface and a back surface, a back electrode deposited on the back surface of the crystal layer and a front metallic electrode including a layer of gold or silver deposited on the front surface of the crystal layer and upon which said film of material accumulates during a deposition process to change the natural oscillation frequency of the crystal, wherein said front surface of the crystal layer is provided with a surface roughness characterized by a mean deviation from true flatness on the order of about 15 to 25 microinches, and said front electrode includes a buffer layer of a conductive metallic material having the following properties: a suitably low bulk modulus and a suitable Young's modulus; said buffer layer being of sufficient thickness so that the buffer layer absorbs strain between the metallic electrode and the film of material being deposited thereon; a good adhesion for the gold or silver of the conductive electrode layer; a suitably high thermal conductivity; and a low acoustic damping characteristic to prevent undue damping of vibrations in the crystal; so as to prevent interfacial stresses during the deposition process from causing early catastrophic failure, and thus to prolong the useful life of the piezoelectric crystal when used as a crystal microbalance in a film deposition process.

Claim 14

A piezoelectric crystal for measurement of the deposition of a film of material, comprising a crystal layer of a piezoelectric crystal material having a front surface and a back surface, a back electrode deposited on the back surface of the crystal layer and a front metallic electrode deposited on the front surface of the crystal layer and upon which said film of material accumulates during a deposition process to change the natural oscillation frequency of the crystal, wherein said front surface of the crystal layer is provided with a surface roughness characterized by a mean deviation front true flatness on the order of about 15 to 25 microinches, and said front electrode includes a buffer layer of a conductive metallic material of suitably low bulk modulus and of sufficient thickness so that the buffer layer absorbs strain between the electrode and the film of material deposited thereon without undue damping of vibrations in the crystal, so as to prevent interfacial stresses during the deposition process from causing early catastrophic crystal failure, and thus to prolong the useful life of the piezoelectric crystal when used as a crystal microbalance in a film deposition process; wherein said buffer layer is selected from the group consisting of aluminum, bismuth, calcium, indium, lead, selenium, silver, tellurium, tin, cadmium and zinc.

Claim 15

A piezoelectric crystal for measurement of the deposition of a film of material, comprising a crystal layer of a piezoelectric crystal material having a front surface and a back surface, a back electrode deposited on the back surface of the crystal layer and a front metallic electrode deposited on the front surface of the crystal layer and upon which said film of material accumulates during a deposition process to change the natural oscillation frequency of the crystal, wherein said front surface of the crystal layer is provided with a surface roughness characterized by a mean deviation front true flatness on the order of about 15 to 25 microinches, and said front electrode includes a buffer layer of a conductive metallic material of suitably low bulk modulus and of sufficient thickness so that the buffer layer absorbs strain between the electrode and the film of material deposited thereon without undue damping of vibrations in the crystal, so as to prevent interfacial stresses during the deposition process from causing early catastrophic crystal failure, and thus to prolong the useful life of the piezoelectric crystal when used as a crystal microbalance in a film deposition process; wherein said buffer layer is selected from the group consisting of aluminum, bismuth, calcium, indium, lead, selenium, silver, tellurium, tin, cadmium and zinc.

Claim 16

The piezoelectric crystal of claim 11, wherein said buffer layer is selected from the group consisting of zinc, cadmium, lead, copper, calcium, and alloys thereof.

Claim 17

The piezoelectric crystal of claim 11 wherein said buffer layer is zinc.

Claim 18

The piezoelectric crystal of claim 11 wherein said front electrode includes a thin adhesive layer of titanium or chromium bonding said buffer layer to said crystal layer.

Claim 19

The piezoelectric crystal of claim 11, wherein said front electrode includes an overlayer of gold, silver, or aluminum.