# Patent

## Title
Thermal bend actuator comprising aluminium alloy

## Abstract

A thermal bend actuator, having a plurality of elements, is provided. The actuator comprises a first active element for connection to drive circuitry a second passive element mechanically cooperating with the first element. When a current is passed through the first element, the first element expands relative to the second element, resulting in bending of the actuator. The first element is comprised of an aluminium alloy.

## Background
FIELD OF THE INVENTION
This invention relates to thermal bend actuators. It has been developed primarily to provide improved inkjet nozzles which eject ink via thermal bend actuation.
CO-PENDING APPLICATIONS
The following applications have been filed by the Applicant simultaneously with the present application:



















IJ71US
IJ72US
IJ73US
IJ74US
IJ75US



KIP002US










The disclosures of these co-pending applications are incorporated herein by reference. The above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.
CROSS REFERENCES
The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.


















09/517,539
6,566,858
6,331,946
6,246,970
6,442,525
09/517,384
09/505,951


6,374,354
09/517,608
6,816,968
6,757,832
6,334,190
6,745,331
09/517,541


10/203,559
10/203,560
7,093,139
10/636,263
10/636,283
10/866,608
10/902,889


10/902,833
10/940,653
10/942,858
10/727,181
10/727,162
10/727,163
10/727,245


7,121,639
10/727,233
10/727,280
10/727,157
10/727,178
7,096,137
10/727,257


10/727,238
10/727,251
10/727,159
10/727,180
10/727,179
10/727,192
10/727,274


10/727,164
10/727,161
10/727,198
10/727,158
10/754,536
10/754,938
10/727,227


10/727,160
10/934,720
11/212,702
11/272,491
11/474,278
11/488,853
11/488,841


10/296,522
6,795,215
7,070,098
09/575,109
6,805,419
6,859,289
6,977,751


6,398,332
6,394,573
6,622,923
6,747,760
6,921,144
10/884,881
7,092,112


10/949,294
11/039,866
11/123,011
6,986,560
7,008,033
11/148,237
11/248,435


11/248,426
11/478,599
11/499,749
10/922,846
10/922,845
10/854,521
10/854,522


10/854,488
10/854,487
10/854,503
10/854,504
10/854,509
10/854,510
7,093,989


10/854,497
10/854,495
10/854,498
10/854,511
10/854,512
10/854,525
10/854,526


10/854,516
10/854,508
10/854,507
10/854,515
10/854,506
10/854,505
10/854,493


10/854,494
10/854,489
10/854,490
10/854,492
10/854,491
10/854,528
10/854,523


10/854,527
10/854,524
10/854,520
10/854,514
10/854,519
10/854,513
10/854,499


10/854,501
10/854,500
10/854,502
10/854,518
10/854,517
10/934,628
11/212,823


11/499,803
11/544,764
11/544,765
11/544,772
11/544,773
11/544,774
11/544,775


11/544,776
11/544,766
11/544,767
11/544,771
11/544,770
11/544,769
11/544,777


11/544,768
11/544,763
10/728,804
7,128,400
7,108,355
6,991,322
10/728,790


7,118,197
10/728,970
10/728,784
10/728,783
7,077,493
6,962,402
10/728,803


10/728,780
10/728,779
7,118,198
10/773,204
10/773,198
10/773,199
6,830,318


10/773,201
10/773,191
10/773,183
7,108,356
7,118,202
10/773,186
10/773,200


10/773,185
10/773,192
10/773,197
10/773,203
10/773,187
10/773,202
10/773,188


7,118,201
7,111,926
10/773,184
7,018,021
11/060,751
11/060,805
11/188,017


7,128,402
11/298,774
11/329,157
11/490,041
11/501,767
11/499,736
11/505,935


11/506,172
11/505,846
11/505,857
11/505,856
11/524,908
11/524,938
11/524,900


11/524,912
11/592,999
11/592,995
6,746,105
10/407,212
10/407,207
10/683,064


10/683,041
6,750,901
6,476,863
6,788,336
11/097,308
11/097,309
11/097,335


11/097,299
11/097,310
11/097,213
11/210,687
11/097,212
11/212,637
11/545,509


10/760,272
10/760,273
7,083,271
10/760,182
7,080,894
10/760,218
7,090,336


10/760,216
10/760,233
10/760,246
7,083,257
10/760,243
10/760,201
10/760,185


10/760,253
10/760,255
10/760,209
7,118,192
10/760,194
10/760,238
7,077,505


10/760,235
7,077,504
10/760,189
10/760,262
10/760,232
10/760,231
10/760,200


10/760,190
10/760,191
10/760,227
7,108,353
7,104,629
11/446,227
11/454,904


11/472,345
11/474,273
11/478,594
11/474,279
11/482,939
11/482,950
11/499,709


11/592,984
10/815,625
10/815,624
10/815,628
10/913,375
10/913,373
10/913,374


10/913,372
10/913,377
10/913,378
10/913,380
10/913,379
10/913,376
7,122,076


10/986,402
11/172,816
11/172,815
11/172,814
11/482,990
11/482,986
11/482,985


11/454,899
11/583,942
11/592,990
60/851,754
11/003,786
11/003,616
11/003,418


11/003,334
11/003,600
11/003,404
11/003,419
11/003,700
11/003,601
11/003,618


11/003,615
11/003,337
11/003,698
11/003,420
6,984,017
11/003,699
11/071,473


11/003,463
11/003,701
11/003,683
11/003,614
11/003,702
11/003,684
11/003,619


11/003,617
11/293,800
11/293,802
11/293,801
11/293,808
11/293,809
11/482,975


11/482,970
11/482,968
11/482,972
11/482,971
11/482,969
11/246,676
11/246,677


11/246,678
11/246,679
11/246,680
11/246,681
11/246,714
11/246,713
11/246,689


11/246,671
11/246,670
11/246,669
11/246,704
11/246,710
11/246,688
11/246,716


11/246,715
11/293,832
11/293,838
11/293,825
11/293,841
11/293,799
11/293,796


11/293,797
11/293,798
11/293,804
11/293,840
11/293,803
11/293,833
11/293,834


11/293,835
11/293,836
11/293,837
11/293,792
11/293,794
11/293,839
11/293,826


11/293,829
11/293,830
11/293,827
11/293,828
11/293,795
11/293,823
11/293,824


11/293,831
11/293,815
11/293,819
11/293,818
11/293,817
11/293,816
10/760,254


10/760,210
10/760,202
10/760,197
10/760,198
10/760,249
10/760,263
10/760,196


10/760,247
10/760,223
10/760,264
10/760,244
7,097,291
10/760,222
10/760,248


7,083,273
10/760,192
10/760,203
10/760,204
10/760,205
10/760,206
10/760,267


10/760,270
10/760,259
10/760,271
10/760,275
10/760,274
7,121,655
10/760,184


10/760,195
10/760,186
10/760,261
7,083,272
11/501,771
11/583,874
11/014,764


11/014,763
11/014,748
11/014,747
11/014,761
11/014,760
11/014,757
11/014,714


11/014,713
11/014,762
11/014,724
11/014,723
11/014,756
11/014,736
11/014,759


11/014,758
11/014,725
11/014,739
11/014,738
11/014,737
11/014,726
11/014,745


11/014,712
11/014,715
11/014,751
11/014,735
11/014,734
11/014,719
11/014,750


11/014,749
11/014,746
11/014,769
11/014,729
11/014,743
11/014,733
11/014,754


11/014,755
11/014,765
11/014,766
11/014,740
11/014,720
11/014,753
11/014,752


11/014,744
11/014,741
11/014,768
11/014,767
11/014,718
11/014,717
11/014,716


11/014,732
11/014,742
11/097,268
11/097,185
11/097,184
11/293,820
11/293,813


11/293,822
11/293,812
11/293,821
11/293,814
11/293,793
11/293,842
11/293,811


11/293,807
11/293,806
11/293,805
11/293,810
09/575,197
7,079,712
09/575,123


6,825,945
09/575,165
6,813,039
6,987,506
7,038,797
6,980,318
6,816,274


7,102,772
09/575,186
6,681,045
6,728,000
09/575,145
7,088,459
09/575,181


7,068,382
7,062,651
6,789,194
6,789,191
6,644,642
6,502,614
6,622,999


6,669,385
6,549,935
6,987,573
6,727,996
6,591,884
6,439,706
6,760,119


09/575,198
6,290,349
6,428,155
6,785,016
6,870,966
6,822,639
6,737,591


7,055,739
09/575,129
6,830,196
6,832,717
6,957,768
09/575,162
09/575,172


09/575,170
7,106,888
7,123,239
11/246,707
11/246,706
11/246,705
11/246,708


11/246,693
11/246,692
11/246,696
11/246,695
11/246,694
11/482,958
11/482,955


11/482,962
11/482,963
11/482,956
11/482,954
11/482,974
11/482,957
11/482,987


11/482,959
11/482,960
11/482,961
11/482,964
11/482,965
11/495,815
11/495,816


11/495,817
11/124,158
11/124,196
11/124,199
11/124,162
11/124,202
11/124,197


11/124,154
11/124,198
11/124,153
11/124,151
11/124,160
11/124,192
11/124,175


11/124,163
11/124,149
11/124,152
11/124,173
11/124,155
11/124,157
11/124,174


11/124,194
11/124,164
11/124,200
11/124,195
11/124,166
11/124,150
11/124,172


11/124,165
11/124,186
11/124,185
11/124,184
11/124,182
11/124,201
11/124,171


11/124,181
11/124,161
11/124,156
11/124,191
11/124,159
11/124,175
11/124,188


11/124,170
11/124,187
11/124,189
11/124,190
11/124,180
11/124,193
11/124,183


11/124,178
11/124,177
11/124,148
11/124,168
11/124,167
11/124,179
11/124,169


11/187,976
11/188,011
11/188,014
11/482,979
11/228,540
11/228,500
11/228,501


11/228,530
11/228,490
11/228,531
11/228,504
11/228,533
11/228,502
11/228,507


11/228,482
11/228,505
11/228,497
11/228,487
11/228,529
11/228,484
11/228,489


11/228,518
11/228,536
11/228,496
11/228,488
11/228,506
11/228,516
11/228,526


11/228,539
11/228,538
11/228,524
11/228,523
11/228,519
11/228,528
11/228,527


11/228,525
11/228,520
11/228,498
11/228,511
11/228,522
111/228,515
11/228,537


11/228,534
11/228,491
11/228,499
11/228,509
11/228,492
11/228,493
11/228,510


11/228,508
11/228,512
11/228,514
11/228,494
11/228,495
11/228,486
11/228,481


11/228,477
11/228,485
11/228,483
11/228,521
11/228,517
11/228,532
11/228,513


11/228,503
11/228,480
11/228,535
11/228,478
11/228,479
11/246,687
11/246,718


11/246,685
11/246,686
11/246,703
11/246,691
11/246,711
11/246,690
11/246,712


11/246,717
11/246,709
11/246,700
11/246,701
11/246,702
11/246,668
11/246,697


11/246,698
11/246,699
11/246,675
11/246,674
11/246,667
11/246,684
11/246,672


11/246,673
11/246,683
11/246,682
11/482,953
11/482,977
6,238,115
6,386,535


6,398,344
6,612,240
6,752,549
6,805,049
6,971,313
6,899,480
6,860,664


6,925,935
6,966,636
7,024,995
10/636,245
6,926,455
7,056,038
6,869,172


7,021,843
6,988,845
6,964,533
6,981,809
11/060,804
11/065,146
11/155,544


11/203,241
11/206,805
11/281,421
11/281,422
11/482,981
11/014,721
11/592,996


D529952
11/482,978
11/482,967
11/482,966
11/482,988
11/482,989
11/482,982


11/482,983
11/482,984
11/495,818
11/495,819
6,988,841
6,641,315
6,786,661


6,808,325
6,712,453
6,460,971
6,428,147
6,416,170
6,402,300
6,464,340


6,612,687
6,412,912
6,447,099
7,090,337
11/478,585
6,913,346
10/853,336


11/000,936
7,032,998
6,994,424
7,001,012
7,004,568
7,040,738
11/026,136


7,131,715
11/026,125
11/026,126
7,097,285
7,083,264
11/315,357
11/450,445


11/472,294
11/503,084
6,227,652
6,213,588
6,213,589
6,231,163
6,247,795


6,394,581
6,244,691
6,257,704
6,416,168
6,220,694
6,257,705
6,247,794


6,234,610
6,247,793
6,264,306
6,241,342
6,247,792
6,264,307
6,254,220


6,234,611
6,302,528
6,283,582
6,239,821
6,338,547
6,247,796
6,557,977


6,390,603
6,362,843
6,293,653
6,312,107
6,227,653
6,234,609
6,238,040


6,188,415
6,227,654
6,209,989
6,247,791
6,336,710
6,217,153
6,416,167


6,243,113
6,283,581
6,247,790
6,260,953
6,267,469
6,588,882
6,742,873


6,918,655
09/835,707
6,547,371
6,938,989
6,598,964
6,923,526
09/835,448


6,273,544
6,309,048
6,420,196
6,443,558
6,439,689
6,378,989
6,848,181


6,634,735
6,299,289
6,299,290
6,425,654
6,902,255
6,623,101
6,406,129


6,505,916
6,457,809
6,550,895
6,457,812
10/296,434
6,428,133
11/144,778


7,080,895
11/144,844
11/478,598
10/882,774
10/884,889
10/922,890
10/922,875


10/922,885
10/922,888
10/922,882
10/922,876
10/922,886
10/922,877
11/071,251


11/071,261
11/159,193
11/491,378
6,938,992
6,994,425
6,863,379
11/015,012


7,066,577
7,125,103
11/450,430
11/545,566
6,764,166
6,652,074
10/510,093


6,682,174
6,648,453
6,682,176
6,998,062
6,767,077
10/760,214
10/962,413


6,988,789
11/006,733
11/013,881
7,083,261
7,070,258
11/026,046
11/064,011


11/064,013
7,083,262
11/080,496
11/083,021
7,036,912
11/087,557
11/084,757


11/281,673
11/442,190
11/525,857
6,485,123
6,425,657
6,488,358
7,021,746


6,712,986
6,981,757
6,505,912
6,439,694
6,364,461
6,378,990
6,425,658


6,488,361
6,814,429
6,471,336
6,457,813
6,540,331
6,454,396
6,464,325


6,435,664
6,412,914
6,550,896
6,439,695
6,447,100
09/900,160
6,488,359


6,623,108
6,698,867
6,488,362
6,425,651
6,435,667
6,527,374
6,582,059


6,513,908
6,540,332
6,679,584
6,857,724
6,652,052
6,672,706
7,077,508


10/698,374
6,935,724
6,927,786
6,988,787
6,899,415
6,672,708
6,644,767


6,874,866
6,830,316
6,994,420
7,086,720
10/982,763
10/992,661
7,066,578


7,101,023
11/225,157
11/272,426
11/349,074
7,137,686
11/501,858
11/583,895


6,916,082
6,786,570
10/753,478
6,848,780
6,966,633
10/728,924
6,969,153


6,979,075
7,132,056
6,832,828
6,860,590
6,905,620
6,786,574
6,824,252


6,890,059
10/913,325
7,125,102
7,028,474
7,066,575
6,986,202
7,044,584


7,032,992
11/015,018
11/030,964
11/048,748
7,008,041
7,011,390
7,048,868


7,014,785
7,131,717
11/176,158
11/202,331
7,104,631
11/202,217
11/231,875


11/231,876
11/298,635
11/329,167
11/442,161
11/442,126
11/478,588
11/525,861


11/583,939
11/545,504
11/583,894
10/882,775
6,932,459
7,032,997
6,998,278


7,004,563
6,938,994
10/959,135
10/959,049
10/962,415
7,077,588
6,918,707


6,923,583
6,953,295
6,921,221
10/992,758
11/008,115
11/012,329
11/084,752


11/084,753
11/185,720
11/177,395
11/202,332
7,101,020
11/336,796
11/442,191


11/525,860
6,945,630
6,830,395
6,641,255
10/309,036
6,666,543
6,669,332


6,663,225
7,073,881
10/636,208
10/636,206
10/636,274
6,808,253
6,827,428


6,959,982
6,959,981
6,886,917
6,863,378
7,052,114
7,001,007
7,008,046


6,880,918
7,066,574
11/036,021
6,976,751
11/071,471
7,080,893
11/155,630


7,055,934
11/155,627
11/159,197
7,083,263
11/472,405
11/484,745
11/503,061


11/544,577
7,067,067
6,776,476
6,880,914
7,086,709
6,783,217
10/693,978


6,929,352
6,824,251
6,834,939
6,840,600
6,786,573
10/713,073
6,799,835


6,938,991
10/884,890
10/884,887
6,988,788
7,022,250
6,929,350
7,004,566


7,055,933
11/144,804
11/165,062
11/298,530
11/329,143
11/442,160
11/442,176


11/454,901
11/442,134
11/499,741
11/525,859
6,866,369
6,886,918
10/882,763


6,921,150
6,913,347
11/033,122
7,093,928
11/072,518
7,086,721
11/171,428


11/165,302
11/144,760
7,111,925
11/455,132
11/546,437
11/584,619









BACKGROUND OF THE INVENTION
The present Applicant has described previously a plethora of MEMS inkjet nozzles using thermal bend actuation. Thermal bend actuation generally means bend movement generated by thermal expansion of one material, having a current passing therethough, relative to another material. The resulting bend movement may be used to eject ink from a nozzle opening, optionally via movement of a paddle or vane, which creates a pressure wave in a nozzle chamber.
Some representative types of thermal bend inkjet nozzles are exemplified in the patents and patent applications listed in the cross reference section above, the contents of which are incorporated herein by reference.
The Applicant's U.S. Pat. No. 6,416,167 describes an inkjet nozzle having a paddle positioned in a nozzle chamber and a thermal bend actuator positioned externally of the nozzle chamber. The actuator takes the form of a lower active beam of conductive material (e.g. titanium nitride) fused to an upper passive beam of non-conductive material (e.g. silicon dioxide). The actuator is connected to the paddle via an arm received through a slot in the wall of the nozzle chamber. Upon passing a current through the lower active beam, the actuator bends upwards and, consequently, the paddle moves towards a nozzle opening defined in a roof of the nozzle chamber, thereby ejecting a droplet of ink. An advantage of this design is its simplicity of construction. A drawback of this design is that both faces of the paddle work against the relatively viscous ink inside the nozzle chamber.
The Applicant's U.S. Pat. No. 6,260,953 (assigned to the present Applicant) describes an inkjet nozzle in which the actuator forms a moving roof portion of the nozzle chamber. The actuator is takes the form of a serpentine core of conductive material encased by a polymeric material. Upon actuation, the actuator bends towards a floor of the nozzle chamber, increasing the pressure within the chamber and forcing a droplet of ink from a nozzle opening defined in the roof of the chamber. The nozzle opening is defined in a non-moving portion of the roof. An advantage of this design is that only one face of the moving roof portion has to work against the relatively viscous ink inside the nozzle chamber. A drawback of this design is that construction of the actuator from a serpentine conductive element encased by polymeric material is difficult to achieve in a MEMS process.
The Applicant's U.S. Pat. No. 6,623,101 describes an inkjet nozzle comprising a nozzle chamber with a moveable roof portion having a nozzle opening defined therein. The moveable roof portion is connected via an arm to a thermal bend actuator positioned externally of the nozzle chamber. The actuator takes the form of an upper active beam spaced apart from a lower passive beam. By spacing the active and passive beams apart, thermal bend efficiency is maximized since the passive beam cannot act as heat sink for the active beam. Upon passing a current through the active upper beam, the moveable roof portion, having the nozzle opening defined therein, is caused to rotate towards a floor of the nozzle chamber, thereby ejecting through the nozzle opening. Since the nozzle opening moves with the roof portion, drop flight direction may be controlled by suitable modification of the shape of the nozzle rim. An advantage of this design is that only one face of the moving roof portion has to work against the relatively viscous ink inside the nozzle chamber. A further advantage is the minimal thermal losses achieved by spacing apart the active and passive beam members. A drawback of this design is the loss of structural rigidity in spacing apart the active and passive beam members.
There is a need to improve upon the design of thermal bend inkjet nozzles, so as to achieve more efficient drop ejection and improved mechanical robustness.
SUMMARY OF THE INVENTION
In a first aspect the present invention provides a thermal bend actuator, having a plurality of elements, comprising:

    
    
        a first active element for connection to drive circuitry; and
        a second passive element mechanically cooperating with the first element, such that when a current is passed through the first element, the first element expands relative to the second element, resulting in bending of the actuator,

wherein the first element is comprised of an aluminium alloy.

    
    


Optionally, said aluminium alloy comprises aluminium and at least one other metal having a Young's modulus of more than 100 GPa.
Optionally, said at least one metal is selected from the group comprising: vanadium, manganese, chromium, cobalt and nickel.
Optionally, said alloy comprises aluminum and vanadium.
Optionally, said alloy comprises at least 80% aluminium.
Optionally, said first and second elements are cantilever beams.
Optionally, the first beam is fused or bonded to the second beam along a longitudinal axis thereof.
Optionally, at least part of the second beam is spaced apart from the first beam, thereby insulating the first beam from at least part of the second beam.
Optionally, one of said plurality of elements is comprised of a porous material
Optionally, said porous material has a dielectric constant of about 2 or less.
Optionally, said porous material is porous silicon dioxide.
Optionally, a third insulation beam is sandwiched between the first beam and the second beam.
Optionally, the third insulation beam is comprised of a porous material.
Optionally, the second beam is comprised of a porous material.
In a further aspect the present invention provides an inkjet nozzle assembly comprising:

    
    
        a nozzle chamber having a nozzle opening and an ink inlet; and
        a thermal bend actuator, having a plurality of cantilever beams, for ejecting ink through the nozzle opening, said actuator comprising:
        a first active beam for connection to drive circuitry; and
        a second passive beam mechanically cooperating with the first beam, such that when a current is passed through the first beam, the first beam expands relative to the second beam, resulting in bending of the actuator, wherein the first beam is comprised of an aluminium alloy.
    
    


Optionally, the nozzle chamber comprises a floor and a roof having a moving portion, whereby actuation of said actuator moves said moving portion towards said floor.
Optionally, the moving portion comprises the actuator.
Optionally, the first active beam defines at least 30% of a total area of the roof.
Optionally, the first active beam defines at least part of an exterior surface of said nozzle chamber.
Optionally, the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor.
In a second aspect the present invention provides a thermal bend actuator, having a plurality of elements, comprising:

    
    
        a first active element for connection to drive circuitry; and
        a second passive element mechanically cooperating with the first element, such that when a current is passed through the first element, the first element expands relative to the second element, resulting in bending of the actuator,

wherein one of said plurality of elements is comprised of a porous material.

    
    


Optionally, said porous material has a dielectric constant of about 2 or less.
Optionally, said porous material is porous silicon dioxide.
Optionally, said first and second elements are cantilever beams.
In a further aspect there is provides a thermal bend actuator further comprising a third insulation beam sandwiched between the first beam and the second beam.
Optionally, the third insulation beam is comprised of a porous material.
Optionally, the first beam is fused or bonded to the second beam along a longitudinal axis thereof.
Optionally, the second beam is comprised of a porous material.
Optionally, the first element is comprised of a material selected from the group comprising: titanium nitride, titanium aluminium nitride and an aluminium alloy.
Optionally, the first element is comprised of an aluminium alloy.
Optionally, said aluminium alloy comprises aluminium and at least one other metal having a Young's modulus of more than 100 GPa.
Optionally, said at least one metal is selected from the group comprising: vanadium, manganese, chromium, cobalt and nickel.
Optionally, said alloy comprises aluminum and vanadium.
Optionally, said alloy comprises at least 80% aluminium.
In another aspect the present invention provides an inkjet nozzle assembly comprising:

    
    
        a nozzle chamber having a nozzle opening and an ink inlet; and
        a thermal bend actuator, having a plurality of cantilever beams, for ejecting ink through the nozzle opening, said actuator comprising:
        a first active beam for connection to drive circuitry; and
        a second passive beam mechanically cooperating with the first beam, such that when a current is passed through the first beam, the first beam expands relative to the second beam, resulting in bending of the actuator, wherein one of said plurality of beams is comprised of a porous material.
    
    


Optionally, the nozzle chamber comprises a floor and a roof having a moving portion, whereby actuation of said actuator moves said moving portion towards said floor.
Optionally, the moving portion comprises the actuator.
Optionally, the first active beam defines at least 30% of a total area of the roof.
Optionally, the first active beam defines at least part of an exterior surface of said nozzle chamber.
Optionally, the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor.
In a third aspect the present invention provides an inkjet nozzle assembly comprising:

    
    
        a nozzle chamber comprising a floor and a roof, said roof having a nozzle opening defined therein, said roof having a moving portion moveable towards the floor; and
        a thermal bend actuator, having a plurality of cantilever beams, for ejecting ink through the nozzle opening, said actuator comprising:
        a first active beam for connection to drive circuitry; and
        a second passive beam mechanically cooperating with the first beam, such that when a current is passed through the first beam, the first beam expands relative to the second beam, resulting in bending of the actuator, wherein said moving portion comprises the actuator.
    
    


Optionally, the first active beam defines at least 30% of a total area of the roof.
Optionally, the first active beam defines at least part of an exterior surface of said roof.
Optionally, the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor portion.
Optionally, the actuator is moveable relative to the nozzle opening.
Optionally, the first beam is defined by a tortuous beam element, said tortuous beam element having a plurality of contiguous beam members.
Optionally, the plurality of contiguous beam members comprises a plurality of longer beam members extending along a longitudinal axis of the first beam, and at least one shorter beam member extending across a transverse axis of the first beam and interconnecting longer beam members.
Optionally, one of said plurality of beams is comprised of a porous material
Optionally, said porous material is porous silicon dioxide having a dielectric constant of 2 or less.
Optionally, the thermal bend actuator further comprises a third insulation beam sandwiched between the first beam and the second beam.
Optionally, the third insulation beam is comprised of a porous material.
Optionally, the first beam is fused or bonded to the second beam.
Optionally, the second beam is comprised of a porous material.
Optionally, at least part of the first beam is spaced apart from the second beam.
Optionally, the first beam is comprised of a material selected from the group comprising: titanium nitride, titanium aluminium nitride and an aluminium alloy.
Optionally, the first beam is comprised of an aluminium alloy.
Optionally, said aluminium alloy comprises aluminium and at least one other metal having a Young's modulus of more than 100 GPa.
Optionally, said at least one metal is selected from the group comprising: vanadium, manganese, chromium, cobalt and nickel.
Optionally, said alloy comprises aluminum and vanadium.
Optionally, said alloy comprises at least 80% aluminium.
In a fourth aspect the present invention provides an inkjet nozzle assembly comprising:

    
    
        a nozzle chamber comprising a floor and a roof, said roof having a nozzle opening defined therein, said roof having a moving portion moveable towards the floor; and
        a thermal bend actuator, having a plurality of cantilever beams, for ejecting ink through the nozzle opening, said actuator comprising:
        a first active beam for connection to drive circuitry; and
        a second passive beam mechanically cooperating with the first beam, such that when a current is passed through the first beam, the first beam expands relative to the second beam, resulting in bending of the actuator,
    
    


Optionally, the first active beam defines at least 30% of a total area of the roof.
Optionally, said moving portion comprises the actuator.
Optionally, the first active beam defines at least part of an exterior surface of said roof.
Optionally, the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor.
Optionally, the actuator is moveable relative to the nozzle opening.
Optionally, the first beam is defined by a tortuous beam element, said tortuous beam element having a plurality of contiguous beam members.
Optionally, the plurality of contiguous beam members comprises a plurality of longer beam members extending along a longitudinal axis of the first beam, and at least one shorter beam member extending across a transverse axis of the first beam and interconnecting longer beam members.
Optionally, one of said plurality of beams is comprised of a porous material
Optionally, said porous material is porous silicon dioxide having a dielectric constant of 2 or less.
Optionally, the thermal bend actuator further comprises a third insulation beam sandwiched between the first beam and the second beam.
Optionally, the third insulation beam is comprised of a porous material.
Optionally, the first beam is fused or bonded to the second beam.
Optionally, the second beam is comprised of a porous material.
Optionally, at least part of the first beam is spaced apart from the second beam.
Optionally, the first beam is comprised of a material selected from the group comprising: titanium nitride, titanium aluminium nitride and an aluminium alloy.
Optionally, the first beam is comprised of an aluminium alloy.
Optionally, said aluminium alloy comprises aluminium and at least one other metal having a Young's modulus of more than 100 GPa.
Optionally, said at least one metal is selected from the group comprising: vanadium, manganese, chromium, cobalt and nickel.
Optionally, said alloy comprises aluminum and vanadium.
Optionally, said alloy comprises at least 80% aluminium.
In a fifth aspect the present invention provides an inkjet nozzle assembly comprising:

    
    
        a nozzle chamber comprising a floor and a roof, said roof having a nozzle opening defined therein, said roof having a moving portion moveable towards the floor; and
        a thermal bend actuator, having a plurality of cantilever beams, for ejecting ink through the nozzle opening, said actuator comprising:
        a first active beam for connection to drive circuitry; and
        a second passive beam mechanically cooperating with the first beam, such that when a current is passed through the first beam, the first beam expands relative to the second beam, resulting in bending of the actuator, wherein the first active beam defines at least part of an exterior surface of said roof.
    
    


Optionally, said moving portion comprises the actuator.
Optionally, the first active beam defines at least 30% of a total area of the roof.
Optionally, the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor.
Optionally, the actuator is moveable relative to the nozzle opening.
Optionally, the first beam is defined by a tortuous beam element, said tortuous beam element having a plurality of contiguous beam members.
Optionally, the tortuous beam element comprises a plurality of longer beam members and at least one shorter beam member, each longer beam member extending along a longitudinal axis of the first beam and being interconnected by a shorter beam member extending across a transverse axis of the first beam.
Optionally, one of said plurality of beams is comprised of a porous material
Optionally, said porous material is porous silicon dioxide having a dielectric constant of 2 or less.
Optionally, the thermal bend actuator further comprises a third insulation beam sandwiched between the first beam and the second beam.
Optionally, the third insulation beam is comprised of a porous material.
Optionally, the first beam is fused or bonded to the second beam.
Optionally, the second beam is comprised of a porous material.
Optionally, at least part of the first beam is spaced apart from the second beam.
Optionally, the first beam is comprised of a material selected from the group comprising: titanium nitride, titanium aluminium nitride and an aluminium alloy.
Optionally, the first beam is comprised of an aluminium alloy.
Optionally, said aluminium alloy comprises aluminium and at least one other metal having a Young's modulus of more than 100 GPa.
Optionally, said at least one metal is selected from the group comprising: vanadium, manganese, chromium, cobalt and nickel.
Optionally, said alloy comprises aluminum and vanadium.
Optionally, said alloy comprises at least 80% aluminium.
In a sixth aspect the present invention provides a thermal bend actuator, having a plurality of elongate cantilever beams, comprising:

    
    
        a first active beam for connection to drive circuitry, said first beam being defined by a tortuous beam element, said tortuous beam element having a plurality of contiguous beam members; and
        a second passive beam mechanically cooperating with the first beam, such that when a current is passed through the first beam, the first beam expands relative to the second beam, resulting in bending of the actuator,

wherein the plurality of contiguous beam members comprises a plurality of longer beam members extending along a longitudinal axis of the first beam, and at least one shorter beam member extending across a transverse axis of the first beam and interconnecting longer beam members.

    
    


Optionally, said first beam is connected to said drive circuitry via a pair of electrical contacts positioned at one end of said actuator.
Optionally, a first electrical contact is connected to a first end of said tortuous beam element and a second electrical contact is connected to a second end of said tortuous beam element.
Optionally, one of said plurality of beams is comprised of a porous material
Optionally, said porous material is porous silicon dioxide having a dielectric constant of 2 or less.
In a further aspect there is provided a thermal bend actuator further comprising a third insulation beam sandwiched between the first beam and the second beam.
Optionally, the third insulation beam is comprised of a porous material.
Optionally, the first beam is fused or bonded to the second beam.
Optionally, the second beam is comprised of a porous material.
Optionally, at least part of the first beam is spaced apart from the second beam.
Optionally, the first beam is comprised of a material selected from the group comprising: titanium nitride, titanium aluminium nitride and an aluminium alloy.
In a further aspect the present invention provides an inkjet nozzle assembly comprising:

    
    
        a nozzle chamber having a nozzle opening and an ink inlet; and
        a thermal bend actuator, having a plurality of cantilever beams, for ejecting ink through the nozzle opening, said actuator comprising:
        a first active beam for connection to drive circuitry, said first beam being defined by a tortuous beam element, said tortuous beam element comprising a plurality of contiguous beam members; and
        a second passive beam mechanically cooperating with the first beam, such that when a current is passed through the first beam, the first element expands relative to the second beam, resulting in bending of the actuator, wherein the plurality of contiguous beam members comprises a plurality of longer beam members extending along a longitudinal axis of the first beam, and at least one shorter beam member extending across a transverse axis of the first beam and interconnecting longer beam members.
    
    


Optionally, the nozzle chamber comprises a floor and a roof having a moving portion, whereby actuation of said actuator moves said moving portion towards said floor.
Optionally, the moving portion comprises the actuator.
Optionally, the first active beam defines at least 30% of a total area of the roof.
Optionally, the first active beam defines at least part of an exterior surface of said nozzle chamber.
Optionally, the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor.
Optionally, the actuator is moveable relative to the nozzle opening.
In a further aspect there is provided an inkjet nozzle assembly further comprising a pair of electrical contacts positioned at one end of said actuator, said electrical contacts providing electrical connection between said tortuous beam element and said drive circuitry.
Optionally, a first electrical contact is connected to a first end of said tortuous beam element and a second electrical contact is connected to a second end of said tortuous beam element.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view of a bi-layered thermal bend actuator comprising an active beam formed from aluminium-vanadium alloy;
FIGS. 2(A)-(C) are schematic side sectional views of an inkjet nozzle assembly comprising a fused thermal bend actuator at various stages of operation;
FIG. 3 is a perspective view of the nozzle assembly shown in FIG. 2(A);
FIG. 4 is a perspective view of part of a printhead integrated circuit comprising an array of nozzle assemblies, as shown in FIGS. 2(A) and 3;
FIG. 5 is a cutaway perspective view of an inkjet nozzle assembly comprising a spaced apart thermal bend actuator and moving roof structure;
FIG. 6 is a cutaway perspective view of the inkjet nozzle assembly shown in FIG. 5 in an actuated configuration;
FIG. 7 is a cutaway perspective view of the inkjet nozzle assembly shown in FIG. 5 immediately after de-actuation;
FIG. 8 is a side sectional view of the nozzle assembly shown in FIG. 6;
FIG. 9 is a side sectional view of an inkjet nozzle assembly comprising a roof having a moving portion defined by a thermal bend actuator;
FIG. 10 is a cutaway perspective view of the nozzle assembly shown in FIG. 9;
FIG. 11 is a perspective view of the nozzle assembly shown in FIG. 10;
FIG. 12 is a cutaway perspective view of an array of the nozzle assemblies shown in FIG. 10;
FIG. 13 is a side sectional view of an alternative inkjet nozzle assembly comprising a roof having a moving portion defined by a thermal bend actuator;
FIG. 14 is a cutaway perspective view of the nozzle assembly shown in FIG. 13;
FIG. 15 is a perspective view of the nozzle assembly shown in FIG. 13;
FIG. 16 is a schematic side view of a tri-layered thermal bend actuator comprising a sandwiched insulating beam formed of porous material; and
FIG. 17 is a schematic side view of a bi-layered thermal bend actuator comprising a passive beam formed of porous material.



DETAILED DESCRIPTION OF THE INVENTION
Thermoelastic Active Element Comprised of Aluminium Alloy
Typically, a MEMS thermal bend actuator (or thermoelastic actuator) comprises a pair of elements in the form of an active element and a passive element, which constrains linear expansion of the active element. The active element is required to undergo greater thermoelastic expansion relative to the passive element, thereby providing a bending motion. The elements may be fused or bonded together for maximum structural integrity or spaced apart for minimizing thermal losses to the passive element.
Hitherto, we described titanium nitride as being a suitable candidate for an active thermoelastic element in a thermal bend actuator (see, for example, U.S. Pat. No. 6,416,167). Other suitable materials described in, for example, Applicant's U.S. Pat. No. 6,428,133 are TiB2, MoSi2 and TiAlN.
In terms of its high thermal expansion and low density, aluminium is strong candidate for use as an active thermoelastic element. However, aluminum suffers from a relatively low Young's modulus, which detracts from its overall thermoelastic efficiency. Accordingly, aluminium had previously been disregarded as a suitable material for use an active thermoelastic element.
However, it has now been found that aluminium alloys are excellent materials for use as thermoelastic active elements, since they combine the advantageous properties of high thermal expansion, low density and high Young's modulus.
Typically, aluminium is alloyed with at least one metal having a Young's modulus of >100 GPa. Typically, aluminium is alloyed with at least one metal selected from the group comprising: vanadium, manganese, chromium, cobalt and nickel. Surprisingly, it has been found that the excellent thermal expansion properties of aluminium are not compromised when alloyed with such metals.
Optionally, the alloy comprises at least 60%, optionally at least 70%, optionally at least 80% or optionally at least 90% aluminium.
FIG. 1 shows a bimorph thermal bend actuator 200 in the form of a cantilever beam 201 fixed to a post 202. The cantilever beam 201 comprises a lower active beam 210 bonded to an upper passive beam 220 of silicon dioxide. The thermoelastic efficiencies of the actuator 200 were compared for active beams comprised of: (i) 100% Al; (ii) 95% Al/5% V; and (iii) 90% Al/10% V.
Thermoelastic efficiencies were compared by stimulating the active beam 210 with a short electrical pulse and measuring the energy required to establish a peak oscillatory velocity of 3 m/s, as determined by a laser interferometer. The results are shown in the Table below:















Energy Required to Reach



Active Beam Material
Peak Oscillatory Velocity









100% Al
466 nJ



95% Al/5% V
224 nJ



90% Al/10% V
219 nJ










Thus, the 95% Al/5% V alloy required 2.08 times less energy than the comparable 100% Al device. Further, the 90% Al/10% V alloy required 2.12 times less energy than the comparable 100% Al device. It was therefore concluded that aluminium alloys are excellent candidates for use as active thermoelastic elements in a range of MEMS applications, including thermal bend actuators for inkjet nozzles.
Inkjet Nozzles Comprising a Thermal Bend Actuator
There now follows a description of typical inkjet nozzles, which may incorporate a thermal bend actuator having an active element comprised of aluminium alloy.
Nozzle Assembly Comprising Fused Thermal Bend Actuator
Turning initially to FIGS. 2(A) and 3, there are shown schematic illustrations of a nozzle assembly 100 according to a first embodiment. The nozzle assembly 100 is formed by MEMS processes on a passivation layer 2 of a silicon substrate 3, as described in U.S. Pat. No. 6,416,167. The nozzle assembly 100 comprises a nozzle chamber 1 having a roof 4 and sidewall 5. The nozzle chamber 1 is filled with ink 6 by means of an ink inlet channel 7 etched through the substrate 3. The nozzle chamber 1 further includes a nozzle opening 8 for ejection of ink from the nozzle chamber. An ink meniscus 20 is pinned across a rim 21 of the nozzle opening 8, as shown in FIG. 2(A).
The nozzle assembly 100 further comprises a paddle 9, positioned inside the nozzle chamber 1, which is interconnected via an arm 11 to an actuator 10 positioned externally of the nozzle chamber. As shown more clearly in FIG. 2, the arm extends through a slot 12 in nozzle chamber 1. Surface tension of ink within the slot 12 is sufficient to provide a fluidic seal for ink contained in the nozzle chamber 1.
The actuator 10 comprises a plurality of elongate actuator units 13, which are spaced apart transversely.
Each actuator unit extends between a fixed post 14, which is mounted on the passivation layer 2, and the arm 11. Hence, the post 14 provides a pivot for the bending motion of the actuator 10.
Each actuator unit 13 comprises a first active beam 15 and a second passive beam 16 fused to an upper face of the active beam. The active beam 15 is conductive and connected to drive circuitry in a CMOS layer of the substrate 3. The passive beam 16 is typically non-conductive.
Referring now to FIG. 2(B), when current flows through the active beam 15, it is heated and undergoes thermal expansion relative to the passive beam 16. This causes upward bending movement of the actuator 10, which is magnified into a rotational movement of the paddle 9.
This consequential paddle movement causes a general increase in pressure around the ink meniscus 20 which expands, as illustrated in FIG. 1(B), in a rapid manner. Subsequently the actuator is deactivated, which causes the paddle 9 to return to its quiescent position (FIG. 2(C)).
During this pulsing cycle, a droplet of ink 17 is ejected from the nozzle opening 8 and at the same time ink 6 reflows into the nozzle chamber 1 via the ink inlet 7. The forward momentum of the ink outside the nozzle rim 21 and the corresponding backflow results in a general necking and breaking off of the droplet 17 which proceeds towards a print medium, as shown in FIG. 2(C). The collapsed meniscus 20 causes ink 6 to be sucked into the nozzle chamber 1 via the ink inlet 7. The nozzle chamber 1 is refilled such that the position in FIG. 2(A) is again reached and the nozzle assembly 100 is ready for the ejection of another droplet of ink.
Turning to FIG. 3, it will be seen that the actuator units 13 are tapered with respect to their transverse axes, having a narrower end connected to the post 14 and a wider end connected to the arm 11. This tapering ensures that maximum resistive heating takes place near the post 14, thereby maximizing the thermoelastic bending motion.
Typically, the passive beam 16 is comprised of silicon dioxide or TEOS deposited by CVD. As shown in the FIGS. 2 to 4, the arm 11 is formed from the same material.
In the present invention, the active beam 15 is comprised of an aluminum alloy, preferably an aluminum-vanadium alloy as described above.
Nozzle Assembly Comprising Spaced Apart Thermal Bend Actuator
Turning now to FIGS. 5 to 8, there is shown a nozzle assembly 300, in accordance with a second embodiment. Referring to FIGS. 5 to 7 of the accompanying drawings, the nozzle assembly 300 is constructed (by way of MEMS technology) on a substrate 301 defining an ink supply aperture 302 opening through a hexagonal inlet 303 (which could be of any other suitable configuration) into a chamber 304. The chamber is defined by a floor portion 305, roof portion 306 and peripheral sidewalls 307 and 308 which overlap in a telescopic manner. The sidewalls 307, depending downwardly from roof portion 306, are sized to be able to move upwardly and downwardly within sidewalls 308 which depend upwardly from floor portion 305.
The ejection nozzle is formed by rim 309 located in the roof portion 306 so as to define an opening for the ejection of ink from the nozzle chamber as will be described further below.
The roof portion 306 and downwardly depending sidewalls 307 are supported by a bend actuator 310 typically made up of layers forming a Joule heated cantilever which is constrained by a non-heated cantilever, so that heating of the Joule heated cantilever causes a differential expansion between the Joule heated cantilever and the non-heated cantilever causing the bend actuator 310 to bend.
The proximal end 311 of the bend actuator is fastened to the substrate 301, and prevented from moving backwards by an anchor member 312 which will be described further below, and the distal end 313 is secured to, and supports, the roof portion 306 and sidewalls 307 of the ink jet nozzle.
In use, ink is supplied into the nozzle chamber through passage 302 and opening 303 in any suitable manner, but typically as described in our previously referenced co-pending patent applications. When it is desired to eject a drop of ink from the nozzle chamber, an electric current is supplied to the bend actuator 310 causing the actuator to bend to the position shown in FIG. 6 and move the roof portion 306 downwardly toward the floor portion 305. This relative movement decreases the volume of the nozzle chamber, causing ink to bulge upwardly through the nozzle rim 309 as shown at 314 (FIG. 6) where it is formed to a droplet by the surface tension in the ink.
As the electric current is withdrawn from the bend actuator 310, the actuator reverts to the straight configuration as shown in FIG. 7 moving the roof portion 306 of the nozzle chamber upwardly to the original location. The momentum of the partially formed ink droplet 314 causes the droplet to continue to move upwardly forming an ink drop 315 as shown in FIG. 7 which is projected on to the adjacent paper surface or other article to be printed.
In one form of the invention, the opening 303 in floor portion 305 is relatively large compared with the cross-section of the nozzle chamber and the ink droplet is caused to be ejected through the nozzle rim 309 upon downward movement of the roof portion 306 by viscous drag in the sidewalls of the aperture 302, and in the supply conduits leading from the ink reservoir (not shown) to the opening 302.
In order to prevent ink leaking from the nozzle chamber during actuation ie. during bending of the bend actuator 310, a fluidic seal is formed between sidewalls 307 and 308 as will now be further described with specific reference to FIGS. 7 and 8.
The ink is retained in the nozzle chamber during relative movement of the roof portion 306 and floor portion 305 by the geometric features of the sidewalls 307 and 308 which ensure that ink is retained within the nozzle chamber by surface tension. To this end, there is provided a very fine gap between downwardly depending sidewall 307 and the mutually facing surface 316 of the upwardly depending sidewall 308. As can be clearly seen in FIG. 8 the ink (shown as a dark shaded area) is restrained within the small aperture between the downwardly depending sidewall 307 and inward faces 316 of the upwardly extending sidewall by the proximity of the two sidewalls which ensures that the ink “self seals” across free opening 317 by surface tension, due to the close proximity of the sidewalls.
In order to make provision for any ink which may escape the surface tension restraint due to impurities or other factors which may break the surface tension, the upwardly depending sidewall 308 is provided in the form of an upwardly facing channel having not only the inner surface 316 but a spaced apart parallel outer surface 18 forming a U-shaped channel 319 between the two surfaces. Any ink drops escaping from the surface tension between the surfaces 307 and 316, overflows into the U-shaped channel where it is retained rather than “wicking” across the surface of the nozzle strata. In this manner, a dual wall fluidic seal is formed which is effective in retaining the ink within the moving nozzle mechanism.
Referring to FIG. 8, it will been seen that the actuator 310 is comprised of a first, active beam 358 arranged above and spaced apart from a second, passive beam 360. By spacing apart the two beams, thermal transfer from the active beam 358 to the passive beam 360 is minimized. Accordingly, this spaced apart arrangement has the advantage of maximizing thermoelastic efficiency. In the present invention, the active beam 358 may be comprised of an aluminium alloy, as described above, such as aluminium-vanadium alloy.
Thermal Bend Actuator Defining Moving Nozzle Roof
The embodiments exemplified by FIGS. 5 to 8 showed a nozzle assembly 300 comprising a nozzle chamber 304 having a roof portion 306 which moves relative to a floor portion 305 of the chamber. The moveable roof portion 306 is actuated to move towards the floor portion 305 by means of a bi-layered thermal bend actuator 310 positioned externally of the nozzle chamber 305.
A moving roof lowers the drop ejection energy, since only one face of the moving structure has to do work against the viscous ink. However, there is still a need to increase the amount of power available for drop ejection. By increasing the amount of power, a shorter pulse width can be used to provide the same amount of energy. With shorter pulse widths, improved drop ejection characteristics can be achieved.
One means for increasing actuator power is to increase the size of the actuator. However, in the nozzle design shown in FIGS. 5 to 8, it is apparent that an increase in actuator size would adversely affect nozzle spacing, which is undesirable in the manufacture of high-resolution pagewidth printheads.
A solution to this problem is provided by the nozzle assembly 400 shown in FIGS. 9 to 12. The nozzle assembly 400 comprises a nozzle chamber 401 formed on a passivated CMOS layer 402 of a silicon substrate 403. The nozzle chamber is defined by a roof 404 and sidewalls 405 extending from the roof to the passivated CMOS layer 402. Ink is supplied to the nozzle chamber 401 by means of an ink inlet 406 in fluid communication with an ink supply channel 407 receiving ink from backside of the silicon substrate. Ink is ejected from the nozzle chamber 401 by means of a nozzle opening 408 defined in the roof 404. The nozzle opening 408 is offset from the ink inlet 406.
As shown more clearly in FIG. 10, the roof 404 has a moving portion 409, which defines a substantial part of the total area of the roof. Typically, the moving portion 409 defines at least 20%, at least 30%, at least 40% or at least 50% of the total area of the roof 404. In the embodiment shown in FIGS. 9 to 12, the nozzle opening 408 and nozzle rim 415 are defined in the moving portion 409, such that the nozzle opening and nozzle rim move with the moving portion.
The nozzle assembly 400 is characterized in that the moving portion 409 is defined by a thermal bend actuator 410 having a planar upper active beam 411 and a planar lower passive beam 412. Hence, the actuator 410 typically defines at least 20%, at least 30%, at least 40% or at least 50% of the total area of the roof 404.
Correspondingly, the upper active beam 411 typically defines at least 20%, at least 30%, at least 40% or at least 50% of the total area of the roof 404.
As shown in FIGS. 9 and 10, at least part of the upper active beam 411 is spaced apart from the lower passive beam 412 for maximizing thermal insulation of the two beams. More specifically, a layer of Ti is used as a bridging layer 413 between the upper active beam 411 comprised of TiN and the lower passive beam 412 comprised of SiO2. The bridging layer 413 allows a gap 414 to be defined in the actuator 410 between the active and passive beams. This gap 414 improves the overall efficiency of the actuator 410 by minimizing thermal transfer from the active beam 411 to the passive beam 412.
However, it will of course be appreciated that the active beam 411 may, alternatively, be fused or bonded directly to the passive beam 412 for improved structural rigidity. Such design modifications would be well within the ambit of the skilled person and are encompassed within the scope of the present invention.
The active beam 411 is connected to a pair of contacts 416 (positive and ground) via the Ti bridging layer. The contacts 416 connect with drive circuitry in the CMOS layers.
When it is required to eject a droplet of ink from the nozzle chamber 401, a current flows through the active beam 411 between the two contacts 416. The active beam 411 is rapidly heated by the current and expands relative to the passive beam 412, thereby causing the actuator 410 (which defines the moving portion 409 of the roof 404) to bend downwards towards the substrate 403. This movement of the actuator 410 causes ejection of ink from the nozzle opening 408 by a rapid increase of pressure inside the nozzle chamber 401. When current stops flowing, the moving portion 409 of the roof 404 is allowed to return to its quiescent position, which sucks ink from the inlet 406 into the nozzle chamber 401, in readiness for the next ejection.
Accordingly, the principle of ink droplet ejection is analogous to that described above in connection with nozzle assembly 300. However, with the thermal bend actuator 410 defining the moving portion 409 of the roof 404, a much greater amount of power is made available for droplet ejection, because the active beam 411 has a large area compared with the overall size of the nozzle assembly 400.
Turning to FIG. 12, it will be readily appreciated that the nozzle assembly 400 (as well as all other nozzle assemblies described herein) may be replicated into an array of nozzle assemblies to define a printhead or printhead integrated circuit. A printhead integrated circuit comprises a silicon substrate, an array of nozzle assemblies (typically arranged in rows) formed on the substrate, and drive circuitry for the nozzle assemblies. A plurality of printhead integrated circuits may be abutted or linked to form a pagewidth inkjet printhead, as described in, for example, Applicant's earlier U.S. application Ser. No. 10/854,491 filed on May 27, 2004 and Ser. No. 11/014,732 filed on Dec. 20, 2004, the contents of which are herein incorporated by reference.
The nozzle assembly 500 shown in FIGS. 13 to 15 is similar to the nozzle assembly 400 insofar as a thermal bend actuator 510, having an upper active beam 511 and a lower passive beam 512, defines a moving portion of a roof 504 of the nozzle chamber 501. Hence, the nozzle assembly 500 achieves the same advantages, in terms of increased power, as the nozzle assembly 400.
However, in contrast with the nozzle assembly 400, the nozzle opening 508 and rim 515 are not defined by the moving portion of the roof 504. Rather, the nozzle opening 508 and rim 515 are defined in a fixed portion of the roof 504 such that the actuator 510 moves independently of the nozzle opening and rim during droplet ejection. An advantage of this arrangement is that it provides more facile control of drop flight direction.
It will of course be appreciated that the aluminium alloys, with their inherent advantage of improved thermal bend efficiency, may be used as the active beam in either of the thermal bend actuators 410 and 510 described above in connection with the embodiments shown in FIGS. 9 to 15.
The nozzle assemblies 400 and 500 may be constructed using suitable MEMS technologies in an analogous manner to inkjet nozzle manufacturing processes exemplified in the Applicant's earlier U.S. Pat. Nos. 6,416,167 and 6,755,509, the contents of which are herein incorporated by reference.
Active Beam Having Optimal Stiffness in a Bend Direction
Referring now to FIGS. 11 and 15, it will be seen that the upper active beams 411 and 511 of the actuators 410 and 510 are each comprised of a tortuous beam element having either a bent (in the case of beam 411) or serpentine (in the case of beam 511) configuration. The tortuous beam element is elongate and has a relatively small cross-sectional area suitable for resistive heating. In addition, the tortuous configuration enables respective ends of the beam element to be connected to respective contacts positioned at one end of the actuator, simplifying the overall design and construction of the nozzle assembly.
Referring specifically to FIGS. 14 and 15, an elongate beam element 520 has a serpentine configuration defining the elongate active cantilever beam 511 of the actuator 510. The serpentine beam element 520 has a planar, tortuous path connecting a first electrical contact 516 with a second electrical contact 516. The electrical contacts 516 (positive and ground) are positioned at one end of the actuator 510 and provide electrical connection between drive circuitry in the CMOS layers 502 and the active beam 511.
The serpentine beam element 520 is fabricated by standard lithographic etching techniques and defined by a plurality of contiguous beam members. In general, beam members may be defined as solid portions of beam material, which extend substantially linearly in, for example, a longitudinal or transverse direction. The beam members of beam element 520 are comprised of longer beam members 521, which extend along a longitudinal axis of the elongate cantilever beam 511, and shorter beam members 522, which extend across a transverse axis of the elongate cantilever beam 511. An advantage of this configuration for the serpentine beam element 520 is that it provides maximum stiffness in a bend direction of the cantilever beam 511. Stiffness in the bend direction is advantageous because it facilitates bending of the actuator 510 back to its quiescent position after each actuation.
It will be appreciated that the bent active beam configuration for the nozzle assembly 400 shown in FIG. 11 achieves the same or similar advantages to those described above in connection with nozzle assembly 500. In FIG. 11, the longer beam members, extending longitudinally, are indicated as 421, whilst the interconnecting shorter beam member, extending transversely, is indicated as 422.
Use of Porous Material for Improving Thermal Efficiency
In all the embodiments described above, as well as all other embodiments of thermal bend actuators described by the present Applicant, the active beam is either bonded to the passive beam for structural robustness (see FIGS. 1 and 2), or the active beam is spaced apart from the passive beam for maximum thermal efficiency (see FIG. 8). The thermal efficiency provided by an air gap between the beams is, of course, desirable. However, this improvement in thermal efficiency is usually at the expense of structural robustness and a propensity for buckling of the thermal bend actuator.
U.S. Pat. No. 6,163,066, the contents of which is incorporated herein by reference, describes a porous silicon dioxide insulator, having a dielectric constant of about 2.0 or less. The material is formed by deposition of silicon carbide and oxidation of the carbon component to form porous silicon dioxide. By increasing the ratio of carbon to silicon, the porosity of the resultant porous silicon dioxide can be increased. Porous silicon dioxide are known to be useful as a passivation layer in integrated circuits for reducing parasitic resistance.
However, the present Applicant has found that porous materials of this type are useful for improving the efficiency of thermal bend actuators. A porous material may be used either as an insulating layer between an active beam and a passive beam, or it may be used as the passive beam itself.
FIG. 16 shows a thermal bend actuator 600 comprising an upper active beam 601, a lower passive beam 602 and an insulating layer 603 sandwiched between the upper and lower beams. The insulating beam is comprised of porous silicon dioxide, while the active and passive beams 601 and 602 may be comprised of any suitable materials, such as TiN and SiO2, respectively.
The porosity of the insulating layer 603 provides excellent thermal insulation between the active and passive beams 601 and 602. The insulating layer 603 also provides the actuator 600 with structural robustness. Hence, the actuator 600 combines the advantages of both types of thermal bend actuator described above in connection with FIGS. 1, 2 and 8.
Alternatively, and as shown in FIG. 17, the porous material may simply form the passive layer of a bi-layered thermal bend actuator. Accordingly, the thermal bend actuator 650 comprises an upper active beam 651 comprised of TiN, and a lower passive beam 652 comprised of porous silicon dioxide.
It will, of course, be appreciated that thermal bend actuators of the types shown in FIGS. 16 and 17 may be incorporated into any suitable inkjet nozzle or other MEMS device. The improvements in thermal efficiency and structural rigidity make such actuators attractive in any MEMS application requiring a mechanical actuator or transducer.
The thermal bend actuators of the types shown in FIGS. 16 and 17 are particularly suitable for use in the inkjet nozzle assemblies 400 and 500 described above. The skilled person would readily appreciate that appropriate modifications of the thermal bend actuators 410 and 510 would realize the above-mentioned improvements in thermal efficiency and structural robustness.
It will be further appreciated that the active beam members 601 and 651 in the thermal bend actuators 600 and 650 described above may be comprised of an aluminum alloy, as described herein, for further improvements in thermal bend efficiency.
It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.

## Claims

1. A thermal bend actuator, having a plurality of elements, comprising:
a first active element for connection to drive circuitry; and
a second passive element mechanically cooperating with the first element, such that when a current is passed through the first element, the first element expands relative to the second element, resulting in bending of the actuator,

wherein the first element is comprised of an aluminium alloy, said aluminium alloy comprising aluminium and at least 5% vanadium.

2. The thermal bend actuator of claim 1, wherein said alloy comprises at least 80% aluminium.

3. The thermal bend actuator of claim 1, wherein said first and second elements are cantilever beams.

4. The thermal bend actuator of claim 3, wherein the first beam is fused or bonded to the second beam along a longitudinal axis thereof.

5. The thermal bend actuator of claim 3, wherein at least part of the second beam is spaced apart from the first beam, thereby insulating the first beam from at least part of the second beam.

6. The thermal bend actuator of claim 1, wherein one of said plurality of elements is comprised of a porous material.

7. The thermal bend actuator of claim 6, wherein said porous material has a dielectric constant of about 2 or less.

8. The thermal bend actuator of claim 6, wherein said porous material is porous silicon dioxide.

9. The thermal bend actuator of claim 3, wherein a third insulation beam is sandwiched between the first beam and the second beam.

10. The thermal bend actuator of claim 9, wherein the third insulation beam is comprised of a porous material.

11. The thermal bend actuator of claim 4, wherein the second beam is comprised of a porous material.

12. An inkjet nozzle assembly comprising:
a nozzle chamber having a nozzle opening and an ink inlet; and
a thermal bend actuator, having a plurality of cantilever beams, for ejecting ink through the nozzle opening, said actuator comprising:
a first active beam for connection to drive circuitry; and
a second passive beam mechanically cooperating with the first beam, such that when

a current is passed through the first beam, the first beam expands relative to the second beam, resulting in bending of the actuator,
wherein the first beam is comprised of an aluminium alloy, said aluminium alloy comprising aluminium and at least 5% vanadium.

13. The inkjet nozzle assembly of claim 12, wherein the nozzle chamber comprises a floor and a roof having a moving portion, whereby actuation of said actuator moves said moving portion towards said floor.

14. The inkjet nozzle assembly of claim 13, wherein the moving portion comprises the actuator.

15. The inkjet nozzle assembly of claim 13, wherein the first active beam defines at least 30% of a total area of the roof.

16. The inkjet nozzle assembly of claim 14, wherein the first active beam defines at least part of an exterior surface of said nozzle chamber.

17. The inkjet nozzle assembly of claim 14, wherein the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor.