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Controlled Q Reduction of a Microwave Cavity and Mode Stabilization

IP.com Disclosure Number: IPCOM000120964D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 61K

Publishing Venue

IBM

Related People

Cuomo, JJ: AUTHOR [+3]

Abstract

A method is disclosed that reduces the precision with which the length of a microwave cavity needs to be controlled. This is especially needed as the cavity dimensions increase to large sizes. Q, which is a quality factor for a cavity, has many equivalent definitions. A convenient one is the energy stored per cycle divided by the energy dissipated per cycle. In a cavity, the 2 main energy losses are due to wall losses and to the load (either a plasma or material being processed). The wall losses are due to the wall electrical conductivity and the surface and near-surface electrical current. The energy is stored in the interior of the cavity. As cavities become larger, the ratio of the cavity volume to the cavity surface area becomes larger, so for a given design, the cavity Q becomes larger with increasing cavity size.

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This is the abbreviated version, containing approximately 64% of the total text.

Controlled Q Reduction of a Microwave Cavity and Mode Stabilization

      A method is disclosed that reduces the precision with which the
length of a microwave cavity needs to be controlled. This is
especially needed as the cavity dimensions increase to large sizes.
Q, which is a quality factor for a cavity, has many equivalent
definitions.  A convenient one is the energy stored per cycle divided
by the energy dissipated per cycle.  In a cavity, the 2 main energy
losses are due to wall losses and to the load (either a plasma or
material being processed).  The wall losses are due to the wall
electrical conductivity and the surface and near-surface electrical
current.  The energy is stored in the interior of the cavity.  As
cavities become larger, the ratio of the cavity volume to the cavity
surface area becomes larger, so for a given design, the cavity Q
becomes larger with increasing cavity size.

      While a very large Q is sometimes desirable, such as when it or
items related to it are used for process diagnostics and control, it
can also have undesirable effects.  The higher the Q of a cavity, the
greater the precision with which the length of the cavity needs to be
controlled to obtain minimum reflected power.  For example, a 14"
cavity having a 10" diameter plasma has a Q of about 40,000.  With
this large cavity Q, the length of the cavity must be controlled to a
few thousands of an inch.  When processing with 1 kW of incident
power, very small varia...