SWITCHING ELEMENTS

BACKGROUND

[0001] Electrostatic discharge (ESD) can damage or destroy components of an integrated circuit (IC). ESD occurs when an accumulated electric charge is shorted to a lower potential. There are many situations in which an ESD event can arise, for example, when a charged body touches an IC and when a charged IC touches a grounded element. When the electric charge moves between surfaces, it becomes a current that can damage the IC. Other elements can also be damaged by an ESD.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The accompanying drawings illustrate various examples of the principles described below. The examples and drawings are illustrative rather than limiting.

[0003] FIG. 1 depicts a diagram of an example printer cartridge that has a printhead with one or multiple memristive elements operating as ESD recording elements.

[0004] FIGS. 2A-2D depict example circuits of memristive elements that record ESD events at a cavitation layer in thermal inkjet printheads.

[0005] FIG. 3 shows an example printhead nozzle and a memristive element that records ESD events at a cavitation layer in the printhead.

[0006] FIG. 4 shows a top view of an example printhead having a single fluid slot formed in a substrate and memristive elements that record ESD events at the cavitation layer in the printhead. [0007] FIG. 5 depicts a flow diagram illustrating an example process of determining whether an electrostatic event occurred at a cavitation layer in a thermal inkjet printhead.

[0008] FIG. 6 depicts a flow diagram illustrating an example process of manufacturing a memristive element as part of a thermal inkjet printhead for detecting whether an ESD event occurred at a cavitation layer in the printhead.

DETAILED DESCRIPTION

[0009] Electrostatic discharge (ESD) may occur without warning and may arise in manufacturing and operating environments. ESD protection circuits have been developed to shunt ESD currents away from circuits in an integrated circuit (IC) that would otherwise be damaged by the discharge. Because thermal inkjet printheads use ICs, ESD protection circuits may be used to protect printhead ICs. Additionally, a cavitation layer is used in thermal inkjet printheads to protect fluid ejectors from fluid corrosion. Because the cavitation layer is not a part of the electrical circuitry of the printhead, it is not protected against ESD damage by existing ESD protection circuits, even though ESD damage to the cavitation layer may compromise yield and printhead life.

[0010] Moreover, a single ESD pulse may be insufficiently strong to damage the cavitation layer, as determined through electrical or fluidic functional testing of the printhead. But if the cavitation layer is subjected to multiple weak ESD pulses, the cavitation layer may be degraded more with each pulse, ultimately resulting in reliability failure that may appear after the fluid ejector has fired an unknown number of times but far fewer than the number of times expected during the lifetime of the printer under warranty. Thus, it would be beneficial to know that the cavitation layer has been subjected to an ESD event before the printer is shipped to the customer.. One way to do so is to use at least one memristive element coupled to each cavitation layer in the printhead to record the occurrence of an ESD event.

[0011 ] As described below, an apparatus in a thermal inkjet printhead for recording the occurrence of an ESD event at a cavitation layer may include a first ejector to eject a first portion of a fluid through a first nozzle; a first cavitation layer covering the first ejector, where the cavitation layer is electrically conductive; and a memristive element, where a first terminal of the memristive element is coupled to the first cavitation layer and a second terminal of the memristive element is coupled to ground. The memristive element switches from a first resistance to a second resistance when an electrostatic discharge (ESD) event occurs at the first cavitation layer, where the first resistance is less than the second resistance.

[0012] In some implementations, the apparatus may further include a second ejector to eject a second portion of the fluid through a second nozzle, where the cavitation layer further covers the second ejector. Alternatively, the apparatus may further include a second ejector to eject a second portion of the fluid through a second nozzle; and a second cavitation layer covering the second ejector, where the second cavitation layer is electrically coupled to the first cavitation layer.

[0013] A memristive element may switch between two or more states, for example, a low resistance state (LRS) and a high resistance state (HRS). With a bipolar memristive element, when voltage is applied to the element in one direction, the element is set to the LRS, and when voltage is applied to the element in the opposite direction, the element is set to the HRS. With a unipolar memristive element, when voltage of a first magnitude is applied to the element, the element is set to the LRS, and when voltage of a second, different magnitude is applied to the element in the same direction, the element is set to the HRS. In both cases, the memristive element remains in the HRS until subsequent switching to the LRS is triggered by the application of a switching voltage or current to the memristive element. By coupling a memristive element to each cavitation layer in a printhead, should an ESD event occur at one of the cavitation layers, the ESD triggers the corresponding memristive element, which is initially set to the LRS, to switch from the LRS to a HRS.

[0014] FIG. 1 depicts a diagram of an example printer cartridge 103 that has an example printhead 1 14 with one or multiple memristive elements 123 operating as ESD recording elements. The printer cartridge 103 may include a printhead 1 14 to carry out at least a part of the functionality of depositing fluid onto a surface, for example, as part of a printer, fax machine, or other multipurpose machine. The printer cartridge 103 may include a fluid chamber 170 to hold a fluid supply for supplying the fluid to the printhead 1 14 for deposition onto a surface. In some examples, the fluid may be ink. For example, the printer cartridge 103 may be an inkjet printer cartridge, the printhead 1 14 may be an inkjet printhead, and the ink may be inkjet ink.

[0015] The printhead 1 14 may include a number of fluid drop generators 125 for depositing fluid onto a surface. For example, components of a fluid drop generator 125 may include an ejector 120 formed on a substrate 1 19, a firing chamber 121 , and a nozzle 1 16. An electrically conductive cavitation layer 129, made from a material such as a metal or alloy, may cover the ejector 120 either directly or indirectly. The cavitation layer 129 should be resistive to corrosion from the fluid. In some implementations, a material of the cavitation layer 129 may be selected from one of: tantalum, titanium, stainless steel, chromium, TaAI, TiN and TaN. The nozzle 1 16 may be a component that includes a small opening through which fluid, such as ink, is deposited onto a surface, such as a print medium. The firing chamber 121 may include a small amount of fluid. The ejector 120 may be a component that ejects fluid through the nozzle 1 16. For example, the ejector 120 may be a firing resistor that heats up in response to an applied voltage. As used herein, and in the appended claims, an "ejector" is a mechanism for ejecting a portion of a fluid through a nozzle 1 16 from a firing chamber 121 , where the ejector 120 may include a firing resistor or other thermal device for ejecting fluid from the firing chamber 121 .

[0016] The printhead 1 14 may also include one or multiple memristive elements 123 to record the occurrence of an ESD event at the cavitation layer 129. Each memristive element 123 may include a first terminal or electrode, a second terminal or electrode, and a switching material sandwiched in between the first and second terminals. The terminals may be any suitable conductive material, such as aluminum, titanium, tantalum, gold, platinum, silver, tungsten, copper, etc., or composites of these conductive materials, such as AICu, AlCuSi, TiN, and TaAI. Further, the first terminal of the memristive element 123 may be coupled to the cavitation layer 129, and a second terminal of the memristive element 123 may be coupled to ground. In some implementations, the memristive element 123 may be coupled to ground via the fluid in the firing chamber 121 .

[0017] FIGS. 2A-2B depict example circuits including a memristive element 215 that records ESD events at a cavitation layer 210 in a thermal inkjet printhead.

[0018] In the example circuit 200A of FIG. 2A, resistor 205 may be a firing resistor or ejector that heats up in response to an applied voltage (not shown). In some examples, the resistor 205 may include a high sheet resistance material, such as TaAI, in parallel with a low resistance material, such as AICu. The resistor 205 may be coated with a passivation layer, such as SiN or SiC or combined layers of SiN and SiC, which has low electrical conductivity. Thus, cavitation layer 210, which covers the resistor 205 over the passivation layer, is not electrically coupled to the resistor 205 and may be floating. A first terminal of memristive element 215 may be coupled to the cavitation layer 210, and the second terminal of the memristive element 215 may be coupled to ground 220, either directly or indirectly. In some examples, the second terminal of the memristive element 215 may be grounded through the fluid or ink to be deposited by the printhead. In the configuration of FIG. 2A, the memristive element 215 may serve as a leakage path for an ESD event. Further, if the memristive element 215 is initially set to a low resistance state, an ESD event that occurs at the cavitation layer 210 may trigger the memristive element 215 to change to a high resistance state. Consequently, the memristive element 215 may be used to record the occurrence of an ESD event through its resistance value.

[0019] In the example circuit 200B of FIG. 2B, resistors 205, 206 are in parallel and may be firing resistors or ejectors that heat up in response to an applied voltage to eject fluid through a nozzle (not shown). A voltage VPP 201 is applied to one terminal of both resistors 205, 206. When a drop of fluid is to be ejected from corresponding nozzles, logic circuitry 225a, 225b may direct corresponding transistors 202a, 202b, coupled to resistors 205, 206, respectively, to close to complete a circuit to allow current to flow through resistors 205, 206, respectively. Resistors 205, 206 may be coated with a single passivation layer, and a single cavitation layer 210 may cover the passivation layer over both resistors 205, 206. As described above, a first terminal of memristive element 215 may be coupled to the cavitation layer 210, and a second terminal of the memristive element 215 may be coupled to ground 220, either directly or indirectly.

[0020] Alternatively, in the example circuit 200C of FIG. 2C, each resistor 205, 206 may be coated with separate cavitation layers 210, 21 1 , and the cavitation layers 210, 21 1 may be electrically coupled.

[0021 ] Yet further, in the example circuit 200D of FIG. 2D, each resistor 205, 206 may be coated with separate cavitation layers 210, 21 1 , and the cavitation layers 210, 21 1 may each be electrically coupled to a respective memristive element 214, 215. A first terminal of each memristive element 214, 215 is coupled to a corresponding cavitation layer 210, 21 1 , and a second terminal of each memristive elements 214, 215 is coupled to ground, either directly or indirectly.

[0022] FIG. 3 an example printhead nozzle 394 and a memristive element 360 that records ESD events at a cavitation layer 384 in the printhead. In the example of FIG. 3, the ejector 380 is a firing resistor ejector. The firing resistor ejector 380 may be formed on a substrate 340, for example, a silicon substrate. The firing resistor ejector 380 may include a high sheet resistance material 381 , such as TaAI, in parallel with a low resistance material 382, such as AICu. As the firing resistor ejector 380 heats up, a portion of the fluid in the firing chamber 396 vaporizes to form a bubble 350. The bubble 350 pushes a drop of fluid 320 out through the nozzle 394 and onto a printing surface (not shown).

[0023] A passivation layer 383, such as SiN or SiC, which has low electrical conductivity, may coat the firing resistor ejector 380. The passivation layer 383 may be between the firing resistor ejector 380 and a cavitation layer 384. In some implementations, a material of the cavitation layer 384 may be selected from one of: tantalum, titanium, stainless steel, chromium, TaAI, TiN and TaN. Other materials that are electrically conductive and resistant to corrosion from the fluid may also be used for the cavitation layer 384. The cavitation layer 384 protects the firing resistor ejector 380 from damage due to the collapsing drive bubble 350.

[0024] Memristive element 360 may also be formed on the substrate 340 to record ESD events occurring at the cavitation layer 384. Memristive element 360 may include a first terminal or electrode 361 , a second terminal or electrode 363, and a switching material 362 sandwiched in between the terminals 361 , 363. The terminals 361 , 363 may be any suitable conductive material, such as aluminum, titanium, tantalum, gold, platinum, silver, tungsten, copper, etc., or composites of these conductive materials, such as AICu, AlCuSi, TiN, and TaAI.

[0025] The switching material 362 may be a switching oxide made of a metallic oxide. Specific examples of switching oxide materials include magnesium oxide, titanium oxide, zirconium oxide, hafnium oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, iron oxide, cobalt oxide, copper oxide, zinc oxide, aluminum oxide, gallium oxide, silicon oxide, germanium oxide, tin dioxide, bismuth oxide, nickel oxide, yttrium oxide, gadolinium oxide, and rhenium oxide, among other oxides. In addition to binary oxides, the switching oxides may be ternary and complex oxides such as silicon oxynitride. The oxides may be formed using a number of different processes such as sputtering from an oxide target, reactive sputtering from a metal target, atomic payer deposition (ALD), or oxidizing a deposited metal or alloy layer.

[0026] FIG. 4 shows a top view of an example printhead 400 having a single fluid slot 401 formed in a substrate 402, for example, a silicon die or substrate. The fluid slot 401 is an elongated slot formed in the substrate 402 that is in fluid communication with a fluid supply (not shown), such as fluid chamber 170 shown in FIG. 1 . In the example of FIG. 4, the fluid slot 401 has multiple ejectors 421 arranged along both sides of the fluidic slot 401 . Although printhead 400 is shown with a single fluid slot 401 , the principles discussed herein are not limited in their application to a printhead with just one fluid slot 401 . Rather, other printhead configurations are also possible, such as printheads with two or more fluid slots. In a thermal inkjet printhead 400, the die/substrate 402 underlies a chamber layer a nozzle layer having nozzles formed therein. However, for the purpose of illustration, the nozzle layer in FIG. 4 is assumed to be transparent in order to show the underlying substrate 402.

[0027] Various components integrated on the printhead die/substrate 402 include firing resistor ejectors 421 , cavitation layers 420a, 420b, and memristive elements 422a, 422b that record ESD events at the cavitation layers 420a, 420b, respectively. In the example of FIG. 4, two separate cavitation layers 420a, 420b are shown, with each cavitation layer covering multiple ejectors 421 , and a single memristive element 422 electrically coupled to each cavitation layer 420. In some implementations, the area of the cavitation layers 420 may be reduced by having each cavitation layer cover fewer ejectors, or even a single ejector, and using multiple cavitation layers. For each cavitation layer 420, one or several memristive elements 422 may be electrically coupled to the cavitation layer 420 to record the occurrence of an ESD event at the coupled cavitation layer 420. Additionally or alternatively, one or several of the cavitation layers 420 may be electrically coupled together.

[0028] FIG. 5 depicts a flow diagram illustrating an example process 500 of determining whether an electrostatic event occurred at a cavitation layer in a thermal inkjet printhead.

[0029] At block 505, a resistance of a memristive element may be determined, where the memristive element may be part of a thermal inkjet printhead. A first terminal of the memristive element may be coupled to a cavitation layer covering an ejector to eject a portion of a fluid from a nozzle, and a second terminal of the memristive element may be coupled to ground. In some implementations, the ejector may be a resistor, and the cavitation layer may cover the resistor, either directly or indirectly. The memristive element switches from a first resistance to a second resistance when an electrostatic discharge (ESD) event occurs at the first cavitation layer. In some implementations, an electrical read circuit may be used to determine a resistance of the memristive element.

[0030] At block 510, from the resistance, it may be determined whether an ESD event occurred at the cavitation layer. If the resistance falls within a first range of resistance values, this indicates no ESD event has occurred. If the resistance falls within a second range of resistance values, this indicates an ESD event occurred at the cavitation layer. In some implementations, values within the first range of resistance values are less than values within the second range of resistance values

[0031 ] In some cases, upon determining that the resistance of the memristive element is within the second range of resistance values, the resistance of the memristive element may be set to a resistance value within the first range of resistance values. By setting the resistance value of the memristive element to the first range of resistance values, the memristive element may subsequently be used to record future ESD events occurring at the cavitation layer.

[0032] FIG. 6 depicts a flow diagram illustrating an example process of manufacturing a memristive element as part of a thermal inkjet printhead for detecting whether an electrostatic event occurred at a cavitation layer in the printhead. At block 605, an ejector may be manufactured to eject a fluid from a nozzle. The ejector may be a resistor, for example, the resistor may include a high sheet resistance material in parallel with a low resistance material. The ejector may also include a passivation layer. At block 610, a cavitation layer may be deposited over the ejector. In some implementations, a passivation layer may be deposited over the ejector, and the cavitation layer may be deposited over the passivation layer.

[0033] At block 615, a memristive element may be manufactured. The memristive element may include a first terminal, a second terminal, and a switching material sandwiched in between the first and second terminals. The terminals may be any suitable conductive material, such as aluminum, titanium, tantalum, gold, platinum, silver, tungsten, copper, etc., or composites of these conductive materials, such as AICu, AlCuSi, TiN, and TaAI. Further, the first terminal of the memristive element may be coupled to the cavitation layer, and a second terminal of the memristive element may be coupled to ground. In some implementations, the memristive element may be coupled to ground via the fluid.

[0034] Not all of the steps, or features presented above are used in each implementation of the presented techniques. Further, steps in process 600 may be performed in a different order than presented.

[0035] As used in the specification and claims herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.