Preconditioned crystals of lithium niobate and lithium tantalate and method of preparing the same

• US 6,319,430 B1
• Filed: 11/05/1999
• Issued: 11/20/2001
• Est. Priority Date: 07/25/1997
• Status: Expired due to Term

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Crystal Technology, Incorporated (Gooch & Housego PLC)
• Inventors: Jundt, Dieter H., Standifer, Eugene M., Bordui, Peter F., Norwood, Richard G.
• Primary Examiner(s): Tucker, Philip
• Application Number:
  US09/434,673
• Time in Patent Office: 746 Days
• Field of Search: 252/584, 252/62.9 R, 117/3, 423/593, 423/598
• US Class Current: 252/584
• CPC Class Codes: C01G 33/00 Compounds of niobium
• CPC Class Codes: C01G 35/00 Compounds of tantalum
• CPC Class Codes: C01P 2006/40 Electric properties
• CPC Class Codes: C01P 2006/60 Optical properties, e.g. expressed in CIELAB-values
• CPC Class Codes: C30B 29/30 Niobates; Vanadates; Tantalates
• CPC Class Codes: C30B 33/00 After-treatment of single crystals or homogeneous polycrystalline material with defined structure C30B31/00 takes precedence

Abstract

Crystals of lithium niobate and lithium tantalate are preconditioned to intentionally increase their electrical conductivity, thus providing crystals with an increased ability to reduce surface charging. Reducing surface charging reduces the risk that the crystals may catastrophically discharge, and adversely affect the performance of devices in which the crystal is incorporated.

Claims

1. A method for preconditioning a lithium niobate or lithium tantalate crystal to increase the crystal'"'"'s ability to reduce electric charging of the crystal surface comprising:

heating the crystal under a chemically reducing atmosphere to a first temperature; and

quenching the crystal by reducing its temperature to below a second temperature of about 250°

C. under a chemically reducing atmosphere;

wherein the chemically reducing atmosphere, the first temperature and the second temperature are selected so that following heating and quenching, a charge decay time of less than one second is required to reduce the surface charge of the crystal to less than 5.0×

10−

11 coulombs as measured at a temperature of 80°

C. following heating to a temperature of 125°

C.

2. The method of claim 1, wherein the crystal is quenched by reducing its temperature to between about 250°

C. to about 100°

C. under a chemically reducing atmosphere.

3. The method of claim 2, further comprising a step of cooling the quenched crystal to room temperature under an oxidizing atmosphere.

4. The method of claim 1, wherein the heating step involves heating the crystal to a temperature greater than 400°

C.

5. The method of claim 4, wherein the heating step involves heating the crystal to a temperature ranging between about 400°

C. to about 1,140°

C.

6. The method of claim 1, wherein the chemically reducing atmosphere comprises gases selected from argon, water, hydrogen, nitrogen, carbon dioxide, carbon monoxide, and combinations thereof.