Dies including strain gauge sensors and temperature sensors

A die includes a plurality of fluid actuation devices and at least one strain gauge sensor to sense strain. The die also includes at least one temperature sensor to sense the temperature of the die to compensate for a temperature component of the sensed strain.

BACKGROUND

An inkjet printing system, as one example of a fluid ejection system, may include a printhead, an ink supply which supplies liquid ink to the printhead, and an electronic controller which controls the printhead. The printhead, as one example of a fluid ejection device, ejects drops of ink through a plurality of nozzles or orifices and toward a print medium, such as a sheet of paper, so as to print onto the print medium. In some examples, the orifices are arranged in at least one column or array such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other.

DETAILED DESCRIPTION

It is desirable to be able to determine the strain at points on a semiconductor die, such as a die including fluid actuation devices (e.g., a fluid ejection die), in the presence of a varying temperature. A varying temperature, however, may affect the output from strain gauge sensors. Accordingly, described herein is a die including at least one strain gauge sensor integrated within the die. The at least one strain gauge sensor senses the strain within the die at the location of the at least one strain gauge sensor. The die also includes at least one temperature sensor to sense the temperature of the die at the location of the at least one strain gauge sensor. The temperature at the at least one strain gauge sensor may be sensed directly by a temperature sensor or interpolated from a plurality of sensed temperatures from a plurality of temperature sensors. The sensed temperature is used to compensate for a temperature component of the sensed strain.

FIG. 1Ais a block diagram illustrating one example of a die10. Die10includes a plurality of fluid actuation devices12, at least one strain gauge sensor14to sense strain, and at least one temperature sensor16. The at least one temperature sensor16senses the temperature of die10to compensate for a temperature component of the sensed strain. In one example, the at least one strain gauge sensor14includes a piezoresistive sensor element, as will be described in detail below with reference toFIG. 2A. In another example, the at least one strain gauge sensor14includes three piezoresistive sensor elements in a rosette configuration, as will be described in detail below with reference toFIG. 2B.

In one example, the at least one temperature sensor16includes a diode, a thermistor, a thermocouple, a silicon bandgap temperature sensor, or another suitable temperature sensor. In another example, the at least one temperature sensor16may include a further strain gauge sensor. The further strain gauge sensor16may include four piezoresistive sensor elements in a Wheatstone bridge configuration (as will be described in detail below with reference toFIG. 3B) co-located with the at least one strain gauge sensor14. In this case, the sensed temperature is based on the difference in the sensed strain between the at least one strain gauge sensor14and the further strain gauge sensor16.

In another example, the at least one temperature sensor16includes a further strain gauge sensor including three piezoresistive sensor elements in a rosette configuration at a location of the fluid ejection die having substantially no stress. Since the output of the further strain gauge sensor16is not affected by stress, the output of the further strain gauge sensor16provides an indication of temperature. Accordingly, in this case, the sensed temperature is based on the difference in the sensed strain between the at least one strain gauge sensor14and the further strain gauge sensor16.

FIG. 1Bis a block diagram illustrating one example of a fluid ejection system20. Fluid ejection system20includes a fluid ejection die21and a controller30. Fluid ejection die21is electrically coupled to controller30through a signal path28. Fluid ejection die21includes a plurality of actuation devices22to eject fluid drops. In one example, actuation devices22are nozzles or fluidic pumps to eject fluid drops. Fluid ejection die21also includes a plurality of strain gauge sensors24to sense strain within the fluid ejection die21and a plurality of temperature sensors26to sense temperature within the fluid ejection die21. Controller30receives the sensed strain from each strain gauge sensor24and the sensed temperature from each temperature sensor26and provides a temperature compensated strain for each sensed strain based on the sensed temperatures.

FIG. 1Cis a block diagram illustrating another example of a fluid ejection system100. Fluid ejection system100includes a fluid ejection assembly, such as printhead assembly102, and a fluid supply assembly, such as ink supply assembly110. In the illustrated example, fluid ejection system100also includes a service station assembly104, a carriage assembly116, a print media transport assembly118, and an electronic controller120. While the following description provides examples of systems and assemblies for fluid handling with regard to ink, the disclosed systems and assemblies are also applicable to the handling of fluids other than ink.

Printhead assembly102includes at least one printhead or fluid ejection die106which ejects drops of ink or fluid through a plurality of orifices or nozzles108. In one example, the drops are directed toward a medium, such as print media124, so as to print onto print media124. In one example, print media124includes any type of suitable sheet material, such as paper, card stock, transparencies, Mylar, fabric, and the like. In another example, print media124includes media for three-dimensional (3D) printing, such as a powder bed, or media for bioprinting and/or drug discovery testing, such as a reservoir or container. In one example, nozzles108are arranged in at least one column or array such that properly sequenced ejection of ink from nozzles108causes characters, symbols, and/or other graphics or images to be printed upon print media124as printhead assembly102and print media124are moved relative to each other.

Fluid ejection die106also includes a plurality of strain gauge sensors107and a plurality of temperature sensors109. The strain gauge sensors107sense strain within fluid ejection die106. In one example, strain gauge sensors107enable fluid ejection system100to monitor the stress experienced by fluid ejection die106. Each strain gauge sensor107exhibits changes in electrical conductivity when corresponding areas of fluid ejection die106are stressed. The amount of stress is quantified by measuring the changes in conductivity. By analyzing the stress at each corresponding area of fluid ejection die106, numerous diagnostics may be performed. The temperature sensors109sense the temperature within fluid ejection die106at the locations of strain gauge sensors107. The sensed temperatures are used to compensate for a temperature component of each sensed strain.

Ink supply assembly110supplies ink to printhead assembly102and includes a reservoir112for storing ink. As such, in one example, ink flows from reservoir112to printhead assembly102. In one example, printhead assembly102and ink supply assembly110are housed together in an inkjet or fluid-jet print cartridge or pen. In another example, ink supply assembly110is separate from printhead assembly102and supplies ink to printhead assembly102through an interface connection113, such as a supply tube and/or valve.

Carriage assembly116positions printhead assembly102relative to print media transport assembly118, and print media transport assembly118positions print media124relative to printhead assembly102. Thus, a print zone126is defined adjacent to nozzles108in an area between printhead assembly102and print media124. In one example, printhead assembly102is a scanning type printhead assembly such that carriage assembly116moves printhead assembly102relative to print media transport assembly118. In another example, printhead assembly102is a non-scanning type printhead assembly such that carriage assembly116fixes printhead assembly102at a prescribed position relative to print media transport assembly118.

Service station assembly104provides for spitting, wiping, capping, and/or priming of printhead assembly102to maintain the functionality of printhead assembly102and, more specifically, nozzles108. For example, service station assembly104may include a rubber blade or wiper which is periodically passed over printhead assembly102to wipe and clean nozzles108of excess ink. In addition, service station assembly104may include a cap that covers printhead assembly102to protect nozzles108from drying out during periods of non-use. In addition, service station assembly104may include a spittoon into which printhead assembly102ejects ink during spits to insure that reservoir112maintains an appropriate level of pressure and fluidity, and to insure that nozzles108do not clog or weep. Functions of service station assembly104may include relative motion between service station assembly104and printhead assembly102.

Electronic controller120communicates with printhead assembly102through a communication path103, service station assembly104through a communication path105, carriage assembly116through a communication path117, and print media transport assembly118through a communication path119. In one example, when printhead assembly102is mounted in carriage assembly116, electronic controller120and printhead assembly102may communicate via carriage assembly116through a communication path101. Electronic controller120may also communicate with ink supply assembly110such that, in one implementation, a new (or used) ink supply may be detected.

Electronic controller120receives data128from a host system, such as a computer, and may include memory for temporarily storing data128. Data128may be sent to fluid ejection system100along an electronic, infrared, optical or other information transfer path. Data128represent, for example, a document and/or file to be printed. As such, data128form a print job for fluid ejection system100and includes at least one print job command and/or command parameter.

In one example, electronic controller120provides control of printhead assembly102including timing control for ejection of ink drops from nozzles108. As such, electronic controller120defines a pattern of ejected ink drops which form characters, symbols, and/or other graphics or images on print media124. Timing control and, therefore, the pattern of ejected ink drops, is determined by the print job commands and/or command parameters. In one example, logic and drive circuitry forming a portion of electronic controller120is located on printhead assembly102. In another example, logic and drive circuitry forming a portion of electronic controller120is located off printhead assembly102.

Electronic controller120also receives the sensed strain from each of the plurality of strain gauge sensors107and the sensed temperature from each of the plurality of temperature sensors109to determine the temperature compensated strain at various locations within fluid ejection die106. Electronic controller120may use the temperature compensated strain at the various locations within fluid ejection die106for numerous purposes, such as to control operations of fluid ejection system100or to alert a user of fluid ejection system100about the status of fluid ejection die106.

FIG. 2Aillustrates one example of a strain gauge sensor200. In one example, strain gauge sensor200provides strain gauge sensor14of die10previously described and illustrated with reference toFIG. 1A, each strain gauge sensor24of fluid ejection die21previously described and illustrated with reference toFIG. 1B, or each strain gauge sensor107of fluid ejection die106previously described and illustrated with reference toFIG. 1C. Strain gauge sensor200includes a first electrode202, a second electrode204, and a piezoresistive sensor element206electrically coupled between first electrode202and second electrode204. Piezoresistive sensor element206exhibits a change in resistance in response to stress in one axis. Therefore, by biasing strain gauge sensor200with a constant current and measuring the voltage across piezoresistive sensor element206or by biasing strain gauge sensor200with a constant voltage and measuring the current through piezoresistive sensor element206, the strain on piezoresistive sensor element206may be sensed.

FIG. 2Billustrates another example of a strain gauge sensor220. In one example, strain gauge sensor220provides strain gauge sensor14of die10previously described and illustrated with reference toFIG. 1A, each strain gauge sensor24of fluid ejection die21previously described and illustrated with reference toFIG. 1B, or each strain gauge sensor107of fluid ejection die106previously described and illustrated with reference toFIG. 1C. Strain gauge sensor220includes a first electrode222, a second electrode224, and a first piezoresistive sensor element226electrically coupled between first electrode222and second electrode224. Strain gauge sensor220also includes a third electrode228, a fourth electrode230, and a second piezoresistive sensor element232electrically coupled between third electrode228and fourth electrode230. Strain gauge sensor220also includes a fifth electrode234, a sixth electrode236, and a third piezoresistive sensor element238electrically coupled between fifth electrode234and sixth electrode236.

Strain gauge sensor220exhibits a change in resistance in response to stress in three directions (e.g., X, Y, and XY). Strain gauge sensor220is configured in a rosette configuration. Accordingly, by biasing each piezoresistive sensor element226,232, and238with a constant current and measuring the voltage across each piezoresistive sensor element226,232, and238, respectively, or by biasing each piezoresistive sensor element226,232, and238with a constant voltage and measuring the current through each piezoresistive sensor element226,232, and238, respectively, the strain on strain gauge sensor220may be sensed.

FIG. 3Aillustrates one example of a strain gauge sensor220co-located with a temperature sensor302. In one example, temperature sensor302provides temperature sensor16previously described and illustrated with reference toFIG. 1A, each temperature sensor26previously described and illustrated with reference toFIG. 1B, or each temperature sensor109previously described and illustrated with reference toFIG. 1C. Strain gauge sensor220was previously described above with reference toFIG. 2B. In this example, temperature sensor302is co-located with strain gauge sensor220adjacent to first electrode222, third electrode228, and fifth electrode234. Temperature sensor302may be a thermistor, a thermocouple, a silicon bandgap temperature sensor, or another suitable temperature sensor.

FIG. 3Billustrates one example of a strain gauge sensor320used to sense temperature. In one example, strain gauge sensor320provides temperature sensor16previously described and illustrated with reference toFIG. 1A, each temperature sensor26previously described and illustrated with reference toFIG. 1B, or each temperature sensor109previously described and illustrated with reference toFIG. 1C. Strain gauge sensor320includes a first electrode322, a second electrode324, a third electrode326, a fourth electrode328, a first piezoresistive sensor element330, a second piezoresistive sensor element331, a third piezoresistive sensor element332, and a fourth piezoresistive sensor element333. First piezoresistive sensor element330is electrically coupled between first electrode322and second electrode324. Second piezoresistive sensor element331is electrically coupled between second electrode324and third electrode326. Third piezoresistive sensor element332is electrically coupled between third electrode326and fourth electrode328. Fourth piezoresistive sensor element333is electrically coupled between fourth electrode328and first electrode322.

Strain gauge sensor320exhibits a change in resistance in response to stress in two axes. Strain gauge sensor320is configured in a Wheatstone bridge configuration in which an external biasing voltage is applied across two opposing electrodes (e.g., first electrode322and third electrode326) while the voltage is measured across the other two opposing electrodes (e.g., second electrode324and fourth electrode328). The Wheatstone bridge configuration is inherently temperature compensated. Therefore, by biasing strain gauge sensor320with an external voltage and measuring the voltage across piezoresistive sensor elements330-333, the inherently temperature compensated strain on strain gauge sensor320may be sensed. The difference in the sensed stain between strain gauge sensor320and a non-inherently temperature compensated strain gauge sensor, such as strain gauge sensor220previously described and illustrated with reference toFIG. 2B, is used to determine the sensed temperature. The sensed temperature may then be used to compensate for the temperature component of the sensed strain from strain gauge sensor220. This may be advantageous since the rosette configuration of strain gauge sensor220provides more information about stress direction than the Wheatstone bridge configuration of strain gauge sensor320.

FIG. 4Aillustrates one example of the output400of a strain gauge sensor with no change in temperature. In this example, the sensor output400is in response to the presence of an oscillating source of stress (e.g., a print carriage moving a printhead back and forth) with no change in temperature.FIG. 4Billustrates one example of the output402of a strain gauge sensor with varying temperature. In this example, the sensor output402is from the same strain gauge sensor as inFIG. 4A, but in the presence of a steep temperature change (e.g., warming as a result of printing or warming in preparation for printing). The sensed stress is overwhelmed by the change in temperature, providing an unusable signal.FIG. 4Cillustrates one example of the output404of a temperature sensor. The temperature sensor is co-located with the strain gauge sensor providing the output signal402ofFIG. 4B. This signal is free of strain information.FIG. 4Dillustrates one example of the temperature compensated output406of a strain gauge sensor. The temperature compensated output406includes the stress information from output signal402ofFIG. 4Bwith the temperature component from the temperature sensor output404ofFIG. 4Cremoved from the signal.

FIG. 5illustrates a front view of one example of a fluid ejection die500. In one example, fluid ejection die500provides fluid ejection die21previously described and illustrated with reference toFIG. 1Bor fluid ejection die106previously described and illustrated with reference toFIG. 1C. Fluid ejection die500includes a plurality of strain gauge sensors co-located with a corresponding plurality of temperatures sensors as indicated by504. In this example, each filled box of504indicates a strain gauge sensor and each empty box of504indicates a temperature sensor. Fluid ejection die500also includes a plurality of bond pads506and a plurality of slots508. Each slot508delivers fluid to a plurality of corresponding nozzles (not shown) adjacent to each slot508. In one example, fluid ejection die500is a silicon die and each of the plurality of strain gauge sensors and co-located temperature sensors504are integrated within the die. Each strain gauge sensor senses the strain within fluid ejection die500at a unique location within fluid ejection die500, and each temperature sensor senses the temperature within fluid ejection die500at the corresponding location of each strain gauge sensor.

A plurality of strain gauge sensors and co-located temperature sensors504may be arranged in at least one column (e.g., three in this example) parallel to slots508. In this example, one column of strain gauge sensors and co-located temperature sensors504are arranged between slots508in the center of fluid ejection die500, and two columns of strain gauge sensors and co-located temperature sensors504are arranged on opposing sides of fluid ejection die500. Strain gauge sensors and co-located temperature sensors504distributed throughout fluid ejection die500may be used to determine a temperature compensated strain profile or stress signature across fluid ejection die500.

Slots508are arranged along the length of fluid ejection die500between bond pads506. A first plurality of strain gauge sensors and co-located temperature sensors504surround a first end of each slot508, and a second plurality of strain gauge sensors and co-located temperature sensors504surround a second end of each slot508. In this example, five strain gauge sensors and co-located temperature sensors504surround each end of each slot508. The ends of slots508are high stress regions within fluid ejection die500due to the silicon slotting process used to form the slots. The strain gauge sensors and co-located temperature sensors504surrounding the ends of each slot508monitor these regions to determine the status of fluid ejection die500.

Bond pads506are arranged on a first end of fluid ejection die500and on a second end of fluid ejection die500opposite to the first end. In another example, bond pads506are also arranged on the side of fluid ejection die500instead of or in addition to the top of fluid ejection die500. Bond pads506electrically couple fluid ejection die500to a fluid ejection system when fluid ejection die500is installed in the system. A plurality of strain gauge sensors and co-located temperature sensors504are proximate bond pads506. In this example, six strain gauge sensors and co-located temperature sensors504are proximate bond pads506(i.e., three strain gauge sensors and co-located temperature sensors504proximate bond pads506on the first end of fluid ejection die500and three strain gauge sensors and co-located temperature sensors504proximate bond pads506on the second end of fluid ejection die500). Bond pads506are high stress regions within fluid ejection die500due to electrical interconnects, bond pad encapsulants, and bond pad adhesives. The strain gauge sensors and co-located temperature sensors504proximate the bond pads506monitor these regions to determine the status of fluid ejection die500. In other examples, strain gauge sensors and co-located temperature sensors504may be arranged at various other locations within fluid ejection die500.

FIG. 6illustrates a front view of another example of a fluid ejection die600. Fluid ejection die600is similar to fluid ejection die500previously described and illustrated with reference toFIG. 5except that in fluid ejection die600some strain gauge sensors and co-located temperature sensors504are replaced with strain gauge sensors604, which do not include a co-located temperature sensor. In this example, fluid ejection die600includes more strain gauge sensors than temperature sensors. Within each column of strain gauge sensors, every other strain gauge sensor includes a co-located temperature sensor. One temperature sensor is arranged at each end of each slot508. In this case, the sensed strain from each strain gauge sensor may be temperature compensated by using the temperature sensed from the co-located temperature sensor if present (e.g., for strain gauge sensors with co-located temperature sensors504), from the nearest temperature sensor (e.g., for the strain gauge sensors604at the ends of each slot508), or by interpolating the temperature at the location of the strain gauge sensor based on the sensed temperatures from at least two temperature sensors (e.g., for the strain gauge sensors604arranged in the columns).

FIG. 7is a flow diagram illustrating one example of a method700for maintaining a fluid ejection system. At702, method700includes sensing the strain at a plurality of locations within a fluid ejection die via strain gauge sensors integrated within the fluid ejection die. In one example, sensing the strain includes sensing the strain in three directions at each of the plurality of locations. At704, method700includes sensing the temperature at the plurality of locations within the fluid ejection die via temperature sensors integrated within the fluid ejection die. In one example, sensing the temperature includes sensing the temperature at each location within the fluid ejection die via a temperature sensor corresponding to each strain gauge sensor. Method700may also include interpolating the temperature at a portion of the plurality of locations based on sensed temperatures from at least two temperature sensors. At706, method700includes compensating the sensed strain from each strain gauge sensor based on the sensed temperatures.