Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1993-05-27
1996-04-30
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310328, 310359, 310364, 347 68, 29 2535, H01L 4108
Patent
active
055127967
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a laminate fop use in the manufacture of printheads for drop-on-demand ink jet printing.
In European Patent No. 0278590 there is described with reference to FIGS. 2(a) and 2(b) a printhead structure of the so-called "chevron" type. This is an advantageous form of structure as it requires a relatively low operating voltage. Further, U.S. Pat. No. 5,016,028 discloses an array printhead of the so-called "cantilever" type which requires a Relatively high operating voltage, in which manufacture takes place from one side of the printhead.
One object of the present invention is to provide a laminate for use in manufacture of an array printhead of the chevron type so that manufacture thereof can take place from one side of the array.
The present invention consists in a co-fired laminate for use in the manufacture of printheads for drop-on-demand ink jet printers, comprising two inner layers of piezo-electric ceramic material which are thickness poled in opposite senses and two outer layers of inactive ceramic material, characterised in that between said inner layers is provided a fifth layer of ceramic material which in response to actuating pulses at the operating temperature of the printhead is substantially insulating and at the poling temperature of the inner layers is substantially conductive duping the poling period.
Suitably, the resistance of said fifth layer lies in a range of approximately 1.5 orders of magnitude. Preferably, the resistance of the fifth layer lies between 75 M.ohms/square and 2500 M.ohms/square at 60.degree. C.
In one form of the invention said fifth layer is a negative temperature coefficient (NTC) ceramic material having a critical temperature between the operating and poling temperatures at which the resistance of said material changes rapidly.
In a further form of the invention said outer layers are formed of an insulating ceramic. Said ceramic suitably is a glass ceramic and may be formed with a dopant to increase the conductivity thereof at the poling temperature.
The invention further consists in the method of forming a drop-on-demand ink jet array printhead comprising
(a) forming a co-fired laminate having two inner layers of piezo-electric material, two outer layers of inactive ceramic material and a fifth layer of ceramic material between said inner layers which is insulating in response to actuating pulses at the operating temperature and at the poling temperature is conductive duping the poling period;
(b) applying electrodes to outer surfaces respectively of said two outer layers;
(c) applying a poling pulse between said fifth layer and said electrodes thereby to effect thickness poling of the inner layers in respective opposite senses;
(d) removing one of the outer layers;
(e) forming an array of parallel channels of depth which extends normal to the laminate through the inner layer from which said one of the outer layers was removed, the middle layer and a substantial part at least of the other of said inner layers; and
(f) applying electrode layers to facing sides of each of said channels.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a cross-sectional view of a laminate according to the invention;
FIG. 2(a) and 2(b) are cross-sectional views of the laminate of FIG. 1 in the course of conversion thereof to an ink jet array printhead component;
FIG. 3 is a diagram of electrical resistance per square of the central layer of the laminate of the earlier Figures against temperature. It illustrates the trend of the minimum resistance appropriate for shear mode wall actuation of a chevron-type of channel wall actuator at room temperature and the trend of the maximum resistance suitable for poling the laminate at the poling temperature;
FIG. 4 is a diagram similar to that of FIG. 3 showing the variation of electrical resistance per square against temperature of the central layer of the laminate when the central layer comprises a negative temperature coefficient material.
Referring
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Budd Mark O.
XAAR Limited
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