ph sensor

Abstract

To sense a pH of a fluid, a heating device of a semiconductor die (102, 105, 107) controls a temperature of the fluid (114) to a first temperature. A first voltage of a gate (122) of a floating gate transistor (120) of the semiconductor die is measured when the temperature of the fluid is at the first temperature. Further, the heating device controls the temperature of the fluid to a second temperature different from the first temperature. A second voltage of the gate is measured when the temperature of the fluid is at the second temperature. The pH of the fluid is determined based on the first voltage and the second voltage, the first temperature and the second temperature.

Description

BACKGROUND

[0001] Sensors can be used to detect the pH of water or other fluids (e.g., liquids). Some pH sensors use an electrolyte-insulator-semiconductor field effect transistor (ISFET) and a chemical reference, such as silver (Ag) / silver chloride (AgCl). These sensors use a reference electrode located within the sensed fluid to obtain an electrical measurement that can be used to characterize the pH of the sensed fluid. However, the reference is complex and expensive to manufacture. In addition, the reference contains a liquid, such as a silver wire coated with AgCl and suspended in a solution including potassium chloride (KCl) + AgCl, with a frit between the reference and the sensed fluid. It is problematic to use a simpler and more cost-effective reference (e.g., platinum (Pt), gold (Au), iridium oxide (IrO x ), ruthenium oxide (RuO2), etc.) because the voltage between the electrode and the fluid can drift irregularly over time. SUMMARY

[0002] In one aspect, a sensor includes a semiconductor die, a transistor, a first electrode, a second electrode, a third electrode, a metal resistor, and a heater circuit. The semiconductor die has a sensing side, a semiconductor substrate, a metallization structure, and a dielectric layer. The metallization structure includes a first level on the semiconductor substrate and a second level between the first level and the sensing side. The dielectric layer is between the sensing side and the second level. The first electrode has a first surface exposed through a first opening in the dielectric layer to couple to a fluid. The second electrode has a second surface exposed through a second opening in the dielectric layer to couple to the fluid. The third electrode is coupled to a transistor gate and separated from the sensing side by the dielectric layer to form a capacitor between the fluid and the gate. The heater circuit has an output coupled to the metal resistor, and the heater circuit is configured to deliver a current signal to the metal resistor to selectively heat the fluid.

[0003] In another aspect, a sensor includes a semiconductor die, a transistor, a heating device, a fluid potential sensing circuit, and a controller. The semiconductor die has a sensing side, a semiconductor substrate, a metallization structure, and a dielectric layer. The metallization structure includes a first electrode, a second electrode, and a third electrode. The first electrode has a first surface exposed through a first opening in the dielectric layer. The second electrode has a second surface exposed through a second opening in the dielectric layer. The third electrode is separated from the first electrode and the second electrode and is separated from the sensing side by the dielectric layer. The transistor has a gate, a drain, and a source. The gate is coupled to the third electrode to sense a potential of a fluid through a capacitor formed by the dielectric layer between the fluid and the third electrode. The heating device has a metal resistor in the metallization structure and a heater circuit in the semiconductor die. The heater circuit has an output coupled to the metal resistor, and the heater circuit is configured to deliver a current signal to the metal resistor to selectively heat the fluid. The fluid potential sensing circuit is coupled to the transistor to provide an output signal representative of the potential of the fluid. The controller is configured to control the heater circuit to control a temperature of the fluid to a first temperature, receive a first sample of the output signal from the fluid potential sensing circuit when the temperature of the fluid is at the first temperature, control the heater circuit to control the temperature of the fluid to a second temperature different from the first temperature, receive a second sample of the output signal from the fluid potential sensing circuit when the temperature of the fluid is at the second temperature, and provide a pH signal representative of a pH of the fluid based on the first sample and the second sample of the output signal, the first temperature, and the second temperature.

[0004] In another aspect, a method includes controlling a temperature of a fluid to a first temperature using a heating device of a semiconductor die and measuring a first voltage of a gate of a floating gate transistor of the semiconductor die when the temperature of the fluid is at the first temperature. The method also includes controlling the temperature of the fluid to a second temperature different from the first temperature using the heating device of the semiconductor die, measuring a second voltage of the gate of the floating gate transistor when the temperature of the fluid is at the second temperature, and determining a pH of the fluid based on the first voltage and the second voltage of the gate, the first temperature, and the second temperature. BRIEF DESCRIPTION OF DRAWINGS

[0005] FIG. 1 is a partial cutaway side view and schematic diagram of a referenceless pH sensor.

[0006] Figure 2 is a top view of a pH sensor. Figure 1

[0007] Figure 3 is a flowchart of a method of sensing a pH using a pH sensor of Figure 1 and Figure 2

[0008] Figure 4 is a flowchart of a method of sensing a pH using a pH sensor of Figure 1 and​​Figure 2 schematic diagram of capacitive coupling in a pH sensor of

[0009] Figure 5 is Figure 1 and Figure 2 schematic diagram of an example fluid potential sensing circuit in a pH sensor of

[0010] Figure 6 is Figure 1 and Figure 2 top-down view of a metal resistor structure in a first metallization level in a pH sensor of

[0011] Figure 7 is Figure 1 and Figure 2 top-down view of an electrode structure in a second metallization level in a pH sensor of Figure 2 .

[0012] Figure 8 is a top-down plan view of sensing sides and surfaces of certain electrodes exposed through respective openings in a dielectric layer in a pH sensor of Figure 1 and Figure 2 .

[0013] Figure 9 is Figure 1 and Figure 2 schematic diagram of an example gating circuit in a pH sensor of

[0014] Figure 10 is Figure 1 and Figure 2 schematic diagram of another example gating circuit in a pH sensor of DETAILED DESCRIPTION

[0015] In the drawings, like reference numerals refer to like elements throughout, and various features not necessarily drawn to scale. Additionally, the term "coupled" includes indirect or direct electrical or mechanical connection or combinations thereof. For example, if a first device is coupled to or with a second device, the connection can be through a direct electrical connection, or through an indirect electrical connection via one or more intervening devices and connections. One or more operational characteristics of various circuits, systems, and / or components are described below in the context of functionality that, in some cases, results from configuration and / or interconnection of various structures when the circuit is powered on and operating.

[0016] Referring initially to Figure 1 and Figure 2 , Figure 1 shows a referenceless (e.g., no reference) sensor 100 including schematic circuit components and partial cross-sectional side elevation structural views taken along line 1-1 in Figure 2 , andFigure 2 A top view of a pH sensor of Figure 1 In one example, the sensor 100 is used to sense the pH of a fluid. The sensor 100 can be used in other applications to sense the pH or another electrical condition of a fluid. The sensor 100 includes a semiconductor die having a sensing side 101. In the illustrated example, the sensing side 101 is a generally planar sensing side on the top of the sensor 100. The sensor 100 includes a semiconductor die having a semiconductor substrate 102, for example, with a lightly doped n- or p-silicon structure, an oppositely doped well 103, and a dielectric layer 104 on a top side thereof. The semiconductor die further includes a metallization structure formed over the dielectric layer 104. The metallization structure includes a first level 105 having a metal pre-metal dielectric (PMD) 106 extending over the semiconductor substrate above the dielectric layer 104. The metallization structure further includes a second level 107 disposed between the first level 105 and the sensing side 101. In another example, the metallization structure includes more than two levels. Figure 1 The second level 107 in includes a first interlayer dielectric (ILD) layer 108, for example, silicon dioxide (SiO2). The illustrated example includes a single ILD level 107 having patterned features 109 formed of conductive aluminum on a top side of the lower PMD layer 106 and covered with the ILD material 108. In other examples, the metallization structure includes any integer number of levels with conductive routing features and conductive contacts or vias for signal routing and / or component interconnection.

[0017] A conductive patterned electrode layer 110 extends over a top side of the ILD layer 108 to form various conductive electrode features as further described below. In one example, the patterned electrode layer 110 is platinum or includes platinum. In operation, the electrical potential of a fluid is set by contact with one or more electrodes of the patterned electrode layer 110, and the exposed one or more electrodes are preferably of or include a material that does not react with the fluid, for example, gold (Au), platinum (Pt), iridium (Ir), iridium oxide (IrOx), palladium (Pd), etc. Ideally, the solution electrical potential is connected externally to the heater so that the voltage potential of the heater to heat the sensing electrode does not change. Certain electrodes of the patterned electrode layer 110 have exposed upper surfaces or sides, for example, as illustrated by the exposed electrode 111. Figure 1 and Figure 2The remaining portions of the patterned electrode layer 110 and the top side of the ILD layer 108 are covered by a dielectric layer 113 that extends between the sensing side 101 and the second level of metallization 107. In one example, the dielectric layer 113 is or includes one or more materials that are stable when in direct contact with the fluid 114. Suitable examples for water pH sensing applications include tantalum pentoxide (Ta2O5), silicon nitride (SiN), aluminum oxide (AlO x ), zirconium oxide (ZrO x ), titanium dioxide (TiO2), silicon oxynitride (SiON), and silicon dioxide (SiO2), aluminum nitride (AIN).

[0018] The top side or surface of the dielectric layer 113 forms an insulating barrier between the covered electrodes and the fluid 114 when installed for use in a pH sensing application. The sensing side 101 is coupled to the fluid 114, such as water or other liquid or gas for sensing pH or other fluid properties, and the sensor 100 can include an encapsulation structure, such as a housing (not shown) that protects the semiconductor die and allows the fluid 114 to be coupled (e.g., directly exposed) to the sensing side 101 of the sensor 100.

[0019] The second level of metallization 107 also includes conductive vias to form electrical connections between select features of the patterned electrode layer 110 and select patterned features 109 on the top side of the PMD layer 106. Figure 1 Two examples are shown, including a via 115 that electrically interconnects an electrode feature 110 with a routing feature 109, and another via 116 that interconnects a floating gate electrode feature 110 with a transistor gate routing feature 109. The PMD layer 106 of the first level 105 includes conductive vias (e.g., tungsten (W)) that electrically interconnect select component terminals (e.g., transistor gates, drains, and sources) to corresponding patterned features 109 for routing to and coupling to electrodes, other components, or circuitry in the semiconductor die.

[0020] Figure 1 Three select cross-sectional side views of portions 117, 118, and 119 of the sensor 100 are shown, their locations indicated in the top view of Figure 2 along corresponding cross-sectional lines 1-1. The portion 117 shows features and aspects of the temperature sensing region of the sensor 100 (labeled “Temperature Sensing” in Figure 1 and “Temperature Sensing (Thermistor)” in Figure 2 . The portion 118 shows features and aspects of the fluid potential sensing region of the sensor 100 (labeled “Fluid Potential Sensing” in Figure 1 and Figure 2Section 119 shows the features and aspects of the fluid potential sensing area of ​​sensor 100. Figure 2 As further shown, the example sensor 100 includes two instances of a fluid potential sensing region having two portions 119, each portion having a generally Figure 1 Features are shown and described further below.

[0021] As in Figure 1 As best shown in FIG, the fluid potential sensing portion 119 of the sensor 100 includes a field effect transistor (FET) 120 having a gate dielectric 121, a gate 122 positioned above the gate dielectric 121, a drain 124, and a source 126. In this example, the drain 124 and the source 126 include a plurality of heavily doped implant regions where the polarity of the dopant is opposite to the polarity of the underlined portion of the substrate 102. In the illustrated example, the transistor 120 is an n-channel transistor. In other examples, the transistor 120 is a p-channel transistor. In one example, the transistor 120 is an extended gate ISFET. The first level 105 of the metallization structure includes tungsten contacts that form electrical connections to the respective gate 122, drain 124, and source 126 of the transistor 122 corresponding to the patterned features 109 in the second level 107. In operation of the sensor 100, the gate voltage VG of the transistor gate 122 is measured for sensing the pH of the fluid 114, as further described below. Figure 1 As shown, portion 118 of sensor 100 includes patterned electrode features 110 having a third surface 130 exposed through a third opening in dielectric layer 113 for coupling to fluid 114 .

[0022] The metallization structure includes patterned features 110 that form various electrodes 131, 132, 133, 134, 135, and 136 for sensing the pH of a fluid 114. In the temperature sensing portion 117, a first electrode 131 is spaced apart from the first electrode 131 in the second level 107 and includes a first surface 111 exposed through a first opening in the dielectric layer 113 for coupling to the fluid 114.

[0023] The second electrode 132 is connected to the Figure 1The first electrode 131 in the second tier 107 in the fluid potential sensing portion 119 is spaced apart. The second electrode 132 includes a second surface 112 exposed through a second opening in the dielectric layer 113 to couple to the fluid 114. In the fluid potential sensing portion 119, the third electrode 133 is spaced apart from the first electrode 131 and the second electrode 132 in the second tier 107. The third electrode 133 is coupled to the gate 122 to sense the potential of the fluid 114. The third electrode 133 is separated from the sensing side 101 by the dielectric layer 113 to form a capacitor 138 between the fluid 114 and the gate 122. The third electrode 133 has no direct contact with the fluid 114. In this example, the fluid 114 above the third electrode 133 forms an upper capacitor plate, and the third electrode 133 forms a lower capacitor plate, and the capacitor plates are separated by the intervening dielectric material of the layer 113 to form the capacitor 138.

[0024] The fourth electrode 134 is in the second tier 107 in the temperature sensing portion 117. The fourth electrode 134 operates as a thermistor coupled through the conductive via 115 to the temperature sensing circuit, as shown. Figure 1 The fourth electrode 134 is spaced apart from the first electrode 131, the second electrode 132, and the third electrode 133. The fourth electrode 134 is separated from the sensing side 101 by the dielectric layer 113, and the fourth electrode 134 has no direct contact with the fluid 114.

[0025] In the portion 118, the fifth electrode 135 is spaced apart from the respective first electrode 131, second electrode 132, and fourth electrode 134 in the second tier 107 of the metallized structure. The fifth electrode 135 is electrically coupled to the third electrode 133, for example, through conductive interconnect routing traces and vias (not shown) in the first tier 105 and the second tier 107, as shown by the dashed line 137 in Figure 1 and Figure 2 The fifth electrode 135 is separated from the sensing side 101 by the dielectric layer 113, and the fifth electrode 135 has no direct contact with the fluid 114. The sixth electrode 136 is spaced apart from the respective first electrode 131, second electrode 132, and third electrode 133, fourth electrode 134, and fifth electrode 135 in the second tier 107 in the fluid potential sensing portion 118. The sixth electrode 136 has a third surface 130 exposed through a third opening in the dielectric layer 113 to couple to the fluid 114.

[0026] The sensor 100 includes a fluid potential sensing circuit 140 in the semiconductor die. The fluid potential sensing circuit 140 is coupled to the transistor 120 and is configured to provide an output signal representative of the electrical potential of the fluid 114. The transistor gate 122 is coupled to the third electrode 133 to sense the electrical potential of the fluid 114 through a capacitor 138 formed by the dielectric layer 113 between the fluid 114 and the third electrode 133. The fluid potential sensing circuit 140 has a first input 141 coupled to the drain 124 of the transistor 120, a second input 142 coupled to the source 126 of the transistor 120, a third input 143 coupled to the body connection of the transistor 120, and an output. The output of the fluid potential sensing circuit is coupled to a controller, as further described below, and is configured to provide an output signal representative of the electrical potential of the fluid 114.

[0027] The sensor 100 includes a heating device having a heater circuit 150 with outputs 151, 152, and 153 in the semiconductor die. The heating device also includes a metal resistor 154 in the second level 107 of the metallization structure. The outputs 151, 152, and 153 of the heater circuit 150 are coupled to the metal resistor 154. The heater circuit 150 is configured to deliver a current signal to the metal resistor 154 to selectively indirectly heat the fluid 114. In one example, the metal resistor 154 is formed from an interconnected aluminum heating fin structure 109 that extends in the respective temperature sensing and fluid potential sensing portions 117 and 118 of the second level 107 of the metallization structure. The metal resistor feature is spaced apart from, but extends beneath and adjacent to, portions of the electrodes 131, 134, 135, and 136 in the second level 107 of the metallization structure.

[0028] As described below in connection with Figure 6Further shown and described, the heater circuit 150 includes a first output 151 coupled to the taps of the respective longitudinal segments of the metal resistor 154. A second output 152 of the heater circuit 150 is coupled to the first end of the respective longitudinal segments of the metal resistor 154, and a third output 153 is coupled to the second end of the respective longitudinal segments of the metal resistor 154. In this example, the second output 152 of the heater circuit 150 is configured to provide a first voltage signal VP that is positive with respect to the voltage VM of the first output 151 of the heater circuit 150. Further, the third output 153 of the heater circuit 150 is configured to provide a second voltage signal VN that is negative with respect to the voltage VM of the first output 151. The positioning of the metal resistor 154 proximate to the sensing side 101 allows the heater circuit 150 to control the temperature of the fluid 114, particularly in the vicinity of the sensing side 101. Further, the temperature control allows for accurate estimation of the pH of the fluid 114 by measuring and sampling the gate voltage VG of the floating gate 122 at different temperatures of the fluid.

[0029] The sensor 100 has a temperature sensing device that includes the fourth electrode 134 and a temperature sensing circuit 160 that operates as a thermistor. As Figure 1As shown, the temperature sensing circuit 160 includes an input 161 that is coupled to the feature 109 in the temperature sensing portion 117 of the sensor 100 and the conductive via 115 to the fourth electrode 134 by a conductor (e.g., aluminum) trace. In one example, the heating (e.g., temperature increase) is very localized in both the fluid 114 and the semiconductor die. In one implementation, the heater / temperature sensor combination determines the temperature increase for a given control signal or determines the required control signal to achieve a target temperature increase. In one example, the fluid potential sensing circuit 140 uses this information to obtain different potentials with and without heating. Further, in one example, the heating occurs in short pulses to mitigate or avoid permanent heating of the chip and the fluid 114 and reduce power consumption. In one example, the heater default state is to close the transmission gate with the heater off. In one example, the sensor implements two phases, including a first phase that employs the temperature sensor to determine the AT or heater control value (heater on versus heater off) and a second phase that senses the fluid potential with the transmission gate open, and the sensor calculates the fluid pH from the two potential samples and the temperature change. In operation, the temperature sensing circuit 160 senses the resistance of the fourth electrode 134 to determine the temperature of the fourth electrode 134. In one example, the temperature sensing circuit 160 includes a current source that selectively applies a predetermined current to one end of the fourth electrode 134 and senses the voltage between the first and second ends of the fourth electrode 134 to determine the electrode resistance. In this example, the temperature sensing circuit 160 includes a voltage sensing circuit and provides an output voltage signal that can be related to the temperature of the fourth electrode 134. Since the fourth electrode 134 is in proximity to the fluid 114, the output voltage signal is representative of the temperature of the fluid 114.

[0030] In one implementation, the output voltage signal from the temperature sensing circuit 160 is provided to a controller that verifies the fluid temperature in order to control the sampling timing of the output of the fluid potential sensing circuit 140 in order to sample the fluid potential sensing output at two or more known temperatures. In another implementation, the output voltage signal from the temperature sensing circuit 160 is provided as a temperature feedback signal to a controller and the controller modifies the operation of the heater circuit 150 to adjust the temperature of the fourth electrode 134 in a closed loop manner.

[0031] In one example, the sensor 100 also includes a gate control circuit 170 (labeled as "floating gate control" in Figure 1 The gate control circuit 170 includes an output 171 coupled to the gate 122, and the gate control circuit 170 is configured to provide an adjustment signal to the gate 122. In one example, the gate control circuit 170 also includes an output 172 coupled to the body connection of the transistor 120, as Figure 1shown. In operation, the gating circuit 170 is used in some examples to reset or stabilize the gate voltage VG of the transistor gate 122 before or after a fluid potential sensing measurement. Example implementations of the gating circuit 170 are described below in connection with Figure 9 and Figure 10 are further illustrated and described.

[0032] The sensor 100 also includes a controller 180 in the semiconductor die. The controller 180 is operably coupled to the fluid potential sensing circuit 140, the heater circuit 150, the temperature sensing circuit 160, and the gating circuit 170 by electrical connections. In one example, the controller 180 includes logic circuitry, e.g., to implement a state machine or perform other logic operations to send control signals to and receive digital signals from the circuits 140, 150, 160, and / or 170. In one example, the controller 180 also includes one or more analog interface circuits, e.g., buffers, amplifiers, analog-to-digital converters, etc. The controller 180 is configured by logic circuitry configuration and / or programming to perform various operations and functions as further described below. In one implementation, the controller 180 controls and / or interfaces with the circuits 140, 150, 160, and / or 170 to continuously sense the pH of the fluid 114 by repeating a series of floating gate voltage measurements at different temperatures. The controller 180 in this implementation provides a pH signal (labeled “PH” in Figure 1 ) at an output 181.

[0033] A side view in Figure 1 shows the sensor 100, Figure 1 with a first lateral direction X and a vertical direction Z. Figure 2 A top view shows one example of the pH sensor 100 in a plane of the first lateral direction X and a second lateral direction Y. Figure 2 A downward top view shows the sensing side of the electrode surface including the top surface of the dielectric layer 113 and the electrodes 131, 132, and 136 exposed through respective first, second, and third openings in the dielectric layer 113. Figure 2 The underlying features and structures covered by the dielectric layer 113 are also shown in dashed lines. Figure 2 These dashed structures in

[0034] Figure 2The sensor implementation in FIG. 1 includes four generally square interior regions 201, 202, 203, and 204 laterally surrounded by the second electrode 132. In this example, region 203 is a second instance of region 201, and region 204 is a second instance of region 202. Other implementations include four such regions or arrangements of a different number of regions. Although regions 201-204 are generally square, other shapes can be used in different examples. In this example, the respective first electrode 131 and fourth electrode 134 are located in the first region 201 (and third region 203) in the second tier 107. In addition, the fifth electrode 135 and sixth electrode 136 are located in the second region 202 (and region 201) in the second tier 107 of the metallization structure. As shown in FIG. 1, regions 201-204 are all spaced apart from one another, with the second region 202 spaced apart from the first region 201. The second electrode 132 laterally surrounds regions 201-204 and has a generally rectangular shape, although not a strict requirement of all possible implementations. Figure 2

[0035] In this example, the respective first electrode 131 and sixth electrode 136 have outer rectangular structures that surround the respective fifth electrode 135 and fourth electrode 136. For example, the first electrode 131 laterally surrounds the fourth electrode 134 in the second metalization tier 107 of the second region 202 and fourth region 204. Similarly, the sixth electrode 136 laterally surrounds the fifth electrode 135 in the second tier 107 of regions 201 and 203. In addition, the respective fourth electrode 134 and fifth electrode 135 have serpentine shapes with elongated segments that extend along the first direction X. The first electrode 131 and sixth electrode 136 have oppositely disposed inwardly extending branch portions that extend along the first direction X between branches of the respective serpentine electrodes 134 and 135. For example, the first electrode 131 has an inwardly extending branch portion that extends along the first direction X between adjacent elongated segments of the fourth electrode 134 in regions 202 and 204, and the sixth electrode 136 has an inwardly extending branch portion that extends along the first direction X between adjacent elongated segments of the first electrode 131 in regions 201 and 203. As shown in FIG. 1, the inwardly extending branch portions of the first electrode 131 and sixth electrode 136 are laterally aligned with one another. Figure 2 As shown in FIG. 1, certain implementations include two or more instances of the fluid potential sensing portion 119, each with a floating gate transistor 120 and associated circuitry as described above in connection with FIG. 1. Figure 1 The electrodes 131 and 136 are substantially equally spaced apart from the respective surrounding serpentine electrodes 134 and 135. In other examples, the electrodes are spaced apart in different amounts. Figure 1 Figure 2 The lateral widths of the electrodes 131, 134, 135, and 136 in FIG. 1 are generally equal. In other examples, the electrodes 131 and 134-136 have different widths.​​

[0036] Figure 3 is shown using Figure 1 and Figure 2 A flowchart of a method 300 of sensing pH using the sensor 100. In one example, the controller 180 is configured to perform the method 300 using one or more of the circuits 140, 150, 160, and / or 170 in Figure 1 In the case where the sensing side 101 of the semiconductor die 102, 105, 107 is coupled to the fluid 114, as shown in Figure 1 the controller 180 implements the method 300 in one or more measurement cycles, one of which is shown in Figure 3 In one implementation, the method 300 includes setting or adjusting the floating gate voltage at 302 and 304 prior to or after measuring the voltage VG of the gate 122. In the example of Figure 3 the controller 302 uses the gating circuit 170 to set the gate voltage VG to a target value at 302. In one example, the controller 180 at 302 causes the gating circuit to close a transmission gate (e.g., described further below in connection with Figure 10 the controller 180 then opens the transmission gate at 304, leaving the transistor gate 122 electrically floating.

[0037] The controller 180 then implements a series of two floating gate voltage measurements at two respective temperatures and calculates a pH value of the fluid based on the two temperatures and the corresponding gate voltage measurements. In one example, at 306, the controller 180 uses the heating device (e.g., the heater circuit 150) to control the temperature of the fluid 114 to a first temperature T1. In one example, this includes setting the fluid temperature to T1, for example, by turning off the heating power supply. In another implementation, the controller 180 controls the power applied by the heater circuit 150 to a non-zero level to set the temperature of the fluid 114 to the first temperature T1. At 308 in Figure 3 the controller 180 uses the temperature sensing circuit 160 to verify that the temperature of the fluid 114 is at or near the desired first temperature T1. In this example, if the temperature is not within a predetermined acceptable range near T1 (NO at 308), the controller 180 continues to monitor the measured temperature at 308.

[0038] Once the temperature is within an acceptable range of the first temperature Tl (YES at 308), the controller 180 measures the floating gate voltage VG at 310 using the fluid potential sensing circuit 140. In one example, the controller 180 receives a first sample of the output signal from the fluid potential sensing circuit 140 at the temperature of the fluid 114 at Tl. In one example, this includes measuring a first voltage VG of the gate 122 at the temperature of the fluid 114 at the first temperature Tl. In one implementation, the gate voltage is sensed directly, for example using a buffer amplifier circuit. In another example, the fluid potential sensing circuit 140 provides a current signal through the channel of the transistor 120 and measures the resulting drain-source voltage between the transistor drain 124 and source 126 to determine the drain-source impedance, and calculates the corresponding floating gate voltage VG based on the sensed drain-source impedance.

[0039] In one example, the controller 180 then causes the heater circuit 150 to control the temperature of the fluid 114 to a second temperature T2. In one implementation, this includes causing the heater circuit 150 to turn on the heating power at 312, and determining whether the measured thermistor temperature is equal to the different second temperature T2 at 314 using the temperature sensing circuit 160. In one example, the controller 180 verifies whether the temperature of the fluid 114 is at or near the desired second temperature T2 at 314 using the temperature sensing circuit 160. In this example, if the temperature is not within a predetermined acceptable range near Tl (NO at 314), the controller 180 continues to monitor the measured temperature at 314. When the temperature is within an acceptable range of T2 (YES at 314), the controller 180 measures a second gate voltage VG at 316 using the fluid potential sensing circuit 140 while the temperature of the fluid 114 is at the second temperature T2.

[0040] At 318, the controller calculates the pH of the fluid 114 based on the first and second voltages VG of the gate 122, the first temperature Tl and the second temperature T2. Thereafter, the method 300 returns to 302 and the controller 180 repeats the method 300 for the next measurement cycle. In one implementation, the controller 180 typically operates continuously to repeat the method 300. In another implementation, the controller 180 implements the measurement cycle as shown in FIG. 3A as needed, for example in response to a request signal from a host circuit (not shown). In one example, the controller 180 receives the request signal from the host circuit at 302. Figure 3 Figure 1 ​The output signal PH is provided at output 181, where, in one example, the output signal PH is an analog voltage or current signal whose amplitude represents the pH of the fluid 114. In another implementation, the output signal PH is a digital value representing the pH of the fluid 114. In one example, the sensor 100 includes a display or other user interface (not shown) that provides continuous readings of the pH value, which is updated as needed or continuously with the most recent pH value calculated at 318.

[0041] In one example operation, the controller 180 includes a computational circuit (e.g., preprogrammed or configured or programmable logic, an arithmetic logic unit (ALU), or a combination thereof) to calculate the pH of the fluid 114. The sensor 100 includes an on-chip heating device located underneath the sensing third electrode 134, which is coupled to the transistor gate 122 to change the local temperature of the fluid 114 at the sensing dielectric interface of the dielectric layer 113 along a portion of the sensing side 101. By measuring the transistor voltage for the same fluid 114 at two different temperatures, the controller 180 uses the Nernst equation to calculate or compute the pH based on the two temperatures T1 and T2 and the corresponding first and second gate voltages VG. The Nernst equation relates the reduction potential to the standard electrode potential, temperature, and concentration, where the cell potential Ecell= E0cell- R*T*LN(X H+ / X0 H+ ) / F, where X is the concentration, X0 is a reference concentration that does not vary with X H+ . Thus, in one example, the controller 180 computes the fluid pH according to the following equation: pH = LOG(X H+ ) = LOG(e)*LN(X H+ ) and provides an output signal (e.g., an analog voltage or current or digital value) at the output 181 according to the computed pH. Certain implementations of the sensor 100 provide a pH sensing solution that does not require an expensive and complex reference, and the sensor 100 measures the solution potential at two temperatures using an extended gate ISFET or other transistor 120. In one implementation, the time between samples is short, e.g., to allow for a transition between the two temperatures. In one example, the sensor 100 uses platinum (Pt) electrodes 131-136 as a reference for sensing the fluid potential, where the floating gate 122 is capacitively coupled by the capacitor 144 and the dielectric layer 113. Further, in the illustrated example, the potential of the fluid 114 is sensed by the surrounding first electrode 131 and the sixth electrode 136 that are exposed to the fluid 114 through respective openings in the dielectric layer 113.

[0042] In the above examples, the controller 180 operates the heater circuit 150 to control the temperature of the fluid 114 to a first predetermined temperature value T1 and a second predetermined temperature value T2. In the illustrated example, the controller 180 also uses the temperature sensing circuit 160 and the thermistor implemented by the fourth electrode 134 to verify when the sensed temperature reaches the desired value and / or to use the heater circuit 150 to provide a temperature feedback signal for closed loop control to control the sensed fluid temperature to the desired value T1 or T2.

[0043] In another possible implementation, the first and second temperatures are not predetermined and the controller 180 uses temperature feedback from the temperature sensing circuit 160. In conjunction with varying control of the heater circuit 150 to measure the first and second gate voltage values VG at two different temperatures. In this implementation, the feedback from the temperature sensing circuit 160 is used to determine the actual values of the different temperatures T1 and T2 for a given measurement cycle and these values are used along with the corresponding first and second gate voltage values VG to calculate the fluid pH at 318. In one example, the controller 180 provides a signal PH at the output 181 representing the pH of the fluid 114 based on the first and second samples of the output signal from the fluid potential sensing circuit 140, the first temperature T1 and the second temperature T2.

[0044] In certain implementations, the controller 180 uses the gating circuit 170 to stabilize or set the gate voltage VG of the floating gate transistor 120 between measurement cycles and each measurement cycle includes measurements at two or more different temperatures, e.g., at the beginning of each pH measurement cycle. In another example, the controller 180 uses the gating circuit 170 to set or adjust the gate voltage VG at the end of a given pH measurement cycle. In another possible implementation, the controller 180 uses the gating circuit 170 to set or adjust the gate voltage VG at different intervals, e.g., after every integer N pH measurement cycles.

[0045] Further, in some implementations, the controller 180 uses the sensed fluid temperature signal or information from the temperature sensing circuit 160 to provide closed loop control and / or verification of the fluid temperature by the heater circuit 150 during the respective measurement cycles. In this regard, in certain examples, the controller 180 determines that the fluid temperature is at the desired value when the feedback from the temperature sensing circuit 160 is within some non-zero tolerance range of the desired value.

[0046] In the illustrated example, the controller 180 provides the first and second temperature values T1 and T2 by operating the heater circuit 150 in a first mode (e.g., a constant current mode) to heat the fluid 114 to the first temperature T1 and a second mode (e.g., a constant voltage mode) to heat the fluid 114 to the second temperature T2. Figure 3implementing on or off temperature control, to refrain from delivering a current signal to the metal resistor 154 (no heating power applied), and receiving the output signal from the fluid potential sensing circuit 140 when the heater circuit 150 refrains from delivering a current signal to the metal resistor 154. In a second mode (e.g., Figure 3 implementing on or off temperature control, to refrain from delivering a current signal to the metal resistor 154 (no heating power applied), and receiving the output signal from the fluid potential sensing circuit 140 when the heater circuit 150 refrains from delivering a current signal to the metal resistor 154. In other implementations, the heater circuit implements different heating control techniques, such as implementing two different fluid temperatures by applying two different amplitude current signals, using pulse width modulation of the current signal to implement two different fluid temperatures, etc., is using open loop control with temperature verification before sampling (e.g., Figure 3 implementing on or off temperature control, to refrain from delivering a current signal to the metal resistor 154 (no heating power applied), and receiving the output signal from the fluid potential sensing circuit 140 when the heater circuit 150 refrains from delivering a current signal to the metal resistor 154. In other implementations, the heater circuit implements different heating control techniques, such as implementing two different fluid temperatures by applying two different amplitude current signals, using pulse width modulation of the current signal to implement two different fluid temperatures, etc., is using open loop control with temperature verification before sampling (e.g.,

[0047] In addition, in certain implementations, the controller 180 computes the pH of the fluid 114 based on sensed fluid potential signal samples obtained at two or more different temperatures and based on the different temperature values. For example, in another implementation, the controller 180 sets or controls the fluid temperature to three or more different temperature values and measures first, second, and third (or more) corresponding gate voltage values VG, and uses the three or more different temperature values and corresponding gate voltage values to compute the fluid pH value at 318.

[0048] In this way, the sensor 100 senses the pH of the fluid 114 without requiring an external reference in the fluid 114. This advantageously reduces cost and complexity compared to pH sensors that use an external reference. In certain examples, selectively using the gating circuit 170 facilitates stability of the fluid potential over time by canceling out drift and other effects.

[0049] Figure 4 shows Figure 1 and Figure 2Schematic diagram of capacitive coupling in a pH sensor of FIG. As schematically represented, the fluid potential sensing capacitor 144 is larger than the other capacitive couplings to the floating gate 122 of the transistor 120. The sensing capacitor 144 provides a capacitive coupling between the floating gate 122 and the fluid potential. Figure 4 The fluid 114 is held at the potential of the exposed electrodes 131 and 136 by direct connection through corresponding openings in the dielectric layer 113, which is Figure 4 In one embodiment, the heater circuit 150 provides a voltage to one end of the metal resistor 154 (at Figure 4 A positive first heater voltage VH+ is provided to the other end of the metal resistor 154 (represented as a first voltage source 406), and a negative second heater voltage VH- is provided to the other end of the metal resistor 154 (represented as a second voltage source 408). These voltages are capacitively coupled to the floating gate 122 of the transistor 120 through a small capacitor.

[0050] like Figure 4 As further shown, another small capacitor represents the parasitic capacitance of the semiconductor die (represented as another voltage source 410) that couples the voltage Vss to the floating gate 122. In one example, the sensor configuration mitigates or prevents the heater capacitance from coupling to the floating gate 122. The metal resistor 154 in the example shown is located directly below the platinum / fluid sensing capacitor 144, which has a large coupling capacitance. In one embodiment, the heater circuit 150 provides a voltage step (VH+, VH-) in the volt range to the metal resistor 154, while the detected signal is in the mV range. As shown below in conjunction with Figure 6 As further described, in one example, the heater circuit 150 advantageously applies symmetrical voltage steps VH+ and VH− to deliver a current signal to the metal resistor 154 during heating.

[0051] Figure 5 An example fluid potential sensing circuit 540 is shown, which can be used as Figure 1 and Figure 2the fluid potential sensing circuit 140 in the pH sensor 100. This example provides a buffer circuit with constant channel charge to provide an output voltage signal representing the voltage VG of the floating gate 122. The buffer circuit includes a first circuit branch 501 and a second circuit branch 502 coupled to a supply voltage terminal 503 having a supply voltage VS. The first circuit branch 501 includes a first current mirror transistor 504, in this example a p-channel FET, and the sensing transistor 120 in series with a first cascode transistor (e.g., n-channel FET) coupled between the supply voltage terminal 503 and a tail current terminal. The second circuit branch 502 includes a second p-channel current mirror transistor 508 coupled in series with a second cascode transistor 510 (e.g., n-channel FET) between the supply voltage terminal 503 and the tail current terminal, and an n-channel transistor 500 structured to have matching dimensions in the semiconductor die as the sensing transistor 120. A cascode voltage reference 512 provides a reference voltage VCAS to the gates of the cascode transistors 506 and 510. The fluid potential sensing circuit 540 includes input terminals 541, 542, and 543 corresponding to the respective input terminals 141, 142, and 143 of the fluid potential sensing circuit 140 in Figure 1 and Figure 2 for interconnection with the drain 124, source 126, and body connection of the sensing transistor 120. This example fluid potential sensing circuit 540 mitigates capacitive coupling back from the sense amplifier to the floating gate 122. In this example, changing the operating conditions of the transistor 120 (e.g., drain current Id, drain-source voltage Vds) causes a change in channel charge, which can be reflected in the floating gate and cause errors. The example buffer circuit 540 and Figure 5 by operating as a differential amplifier with negative feedback, the sensing transistor 120 is provided with a substantially constant drain current Id and a substantially constant drain-source voltage Vds. In this way, the constant tail current ITAIL is distributed substantially equally between the floating gate sensing transistor 120 and the reference transistor 500, thereby providing a substantially constant drain current Id through the sensing transistor 120. The cascode transistors 506 and 510 are used to regulate the drain-source voltage Vds to a constant value across both transistors 120 and 500. The reference voltage source 512 sets the constant drain-source voltage Vds. The circuit mirrors the output of the transistors 504 and 508 to set the floating gate voltage, and device parameter variations are completely or substantially eliminated by good matching to mitigate process, temperature, and voltage variations in the manufacture and operation of the sensor 100.

[0052] Referring to Figures 6-8 , Figure 6 is shown in Figure 1 and Figure 2The first metallization level 105 of the pH sensor 100 Figure 1 and Figure 2 A top view of an example structure of a metal resistor 154 is shown. Figure 7 shows a top view of the electrode structures 131 , 132 , 133 , 134 , 135 and 136 and the second metallization level 107 , and Figure 8 Shown by Figure 1 and Figure 2 A top view of the sensing side and surface of certain electrodes exposed by corresponding openings in the dielectric layer of the pH sensor of FIG. In each of the example regions 201-204 in this example, the metal resistor 154 ( Figure 6 ) is constructed as a serpentine pattern of six turns of conductive metal (e.g., aluminum) patterned features 109 and first metallization level 105. Each of these patterns has a first end coupled to second output 152 of heater circuit 150 having voltage VP, a second end coupled to third output 153 (having voltage VN), and a center tap or intermediate connection coupled to first output 151 having intermediate voltage VM. Metal resistor 154 (e.g., Figure 1 ) is located directly below the platinum electrode for heating, including directly below the sensing area associated with the third electrode 133 and the sensing capacitor 138. In fact, in one example, the fluid 114 (e.g., water) only needs to be heated near the sensing side 101 of the sensor 100, for example, within about 10 nm from the surface of the sensing area. Using a fine pitch for the spacing of the turns of the metal resistor 154 gives a more uniform heat distribution. The thermal conductivity of the platinum electrode and the sensing area also contributes to the uniform heat distribution. The finer spacing between the turns of the serpentine pattern of conductive metal can be combined with dividing the heater into parallel heater segments to stay within a given supply voltage. In one example, the center tap facilitates low capacitance coupling into the floating node of the gate 122.

[0053] As above combined Figure 2The example metal resistor 154 includes a longitudinal segment having respective first and second ends and a tap between the first and second ends. The respective longitudinal segments extend in the second direction Y in the second tier 107. The heater circuit 150 includes a first output 151 coupled to the taps of the respective longitudinal segments, a second output 152 coupled to the first ends of the respective longitudinal segments, and a third output 153 coupled to the second ends of the respective longitudinal segments. The second output 152 of the heater circuit 150 provides a first voltage signal (VP) that is positive with respect to the voltage (VM) of the first output 151, and the third output 153 of the heater circuit 150 provides a second voltage signal (VN) that is negative with respect to the voltage VM of the first output 151. This heater configuration mitigates the effects of capacitive coupling of the metal resistor 154 and the floating gate 122 of the transistor 120.

[0054] In one implementation, the heater circuit 150 applies a positive voltage step at VH+ and a negative voltage step of the same magnitude at VH- at the second and third outputs 152 and 153, respectively. The symmetric voltage steps in this example are achieved by using a middle tap at the first output 151 and using pull-up and pull-down transistors at the positive (VH+) and negative (VH-) pins. When the pull-up and pull-down transistors are off, the voltage of the coupled capacitor is determined by the middle voltage VM. When the pull-up and pull-down transistors are turned on in a symmetric fashion, the middle node only needs to draw a small amount of current caused by defects, and any such defects in semiconductor die manufacturing have the same coupled capacitance for VH+ and VH-, for example by using a platinum electrode and a metal resistor layout in which the serpentine turn portions of the metal resistor 154 and the sensing regions of the platinum electrode are orthogonal with respect to each other. In this example, the turns of the metal resistor 154 generally extend in the Y direction, while the elongated portions of the serpentine sensing electrodes 134 and 135 extend in the X direction.

[0055] In this way, the differences between the coupled capacitors in the positive and negative legs are minimized by default. A second measurement can be performed by applying a positive voltage step at VH+ and a negative voltage step at VH- and averaging the two results, thereby canceling out the effects of any asymmetry between the coupled capacitances. Even if the coupling is actually distributed, the asymmetry cancellation still holds. H- H+

[0056] Figure 9 An example gate circuit 970 is shown that can be used as the gate circuit 970 described above Figure 1 and Figure 2 ​​The gate control circuit 970 is implemented in the form of a first control transistor 901 and a second control transistor 902, which are connected to the gate of the pH sensor 170 by a thin gate oxide 121 ( Figure 1 ) to set or adjust the floating gate voltage VG. In this example, the controller 180 controls the gating circuit 970 to set or adjust the gate voltage VG before or after sampling the output signal from the fluid potential sensing circuit 140. Figure 9 The gate control circuit 970 in FIG. 1 includes a first control transistor 901, a second control transistor 902, a first voltage source 910, and a second voltage source 920. The first control transistor 901 has a first control gate 911, a first control drain 912, and a first control source 913. Figure 9 As shown, first control gate 911 is coupled to floating gate 122 of floating gate transistor 120, and first control drain 912 is coupled to first voltage source 910. Second control transistor 902 has second control gate 921, second control drain 922, and second control source 923. Second control gate 921 is coupled to gate 122, and second control drain 922 is coupled to second voltage source 920. In one example, gate dielectric or gate oxide 121 has a thickness of approximately 70 nm, and the semiconductor die includes as shown. Figure 9 A first control transistor 901 and a second control transistor 902 are shown coupled, wherein the gates of the control transistors are coupled to the floating gate 122. Tunneling effects add or remove charge from the floating gate 122. In the example shown, a positive programming voltage progp from a voltage source 920 adds charge to the floating gate 122, while a negative programming voltage progn from a voltage source 910 subtracts charge from the floating gate 122. In one embodiment, the expected stability of the floating gate voltage VG is within a range of approximately 12 V for a program voltage of approximately 12 V.

[0057] Figure 10 shows that it can be used as above Figure 1 and Figure 2 Another example of a gating circuit 1070 in a pH sensor of the present invention is shown. This embodiment uses a transmission gate 1000 to selectively couple the floating gate 122 to a voltage reference at a target voltage value to set or adjust the floating gate voltage VG. Transmission gate 1000 includes a p-channel transistor 1001 and an n-channel transistor 1002. P-channel transistor 1001 has a first gate 1011, a first drain 1012, a first source 1013, and a first body connection 1014.

[0058] The n-channel transistor 1002 has a second gate 1021, a second drain 1022, a second source 1023, and a second body connection 1024. The second gate 1021 of the n-channel transistor 1002 is coupled to a control input 1040 that receives a control signal from the controller 180, having an active high state that turns on the transistors 1001 and 1002 and a low state that turns off the transistors 1001 and 1002. The first drain 1012 of the p-channel transistor 1001 is coupled to the gate 122, and the second drain 1022 of the n-channel transistor 1002 is coupled to the gate 122. The gate circuit 1070 in this example also includes a voltage source 1030, the output 1031 of which is coupled to the first source 1013 of the p-channel transistor 1001 and the second source 1023 of the n-channel transistor 1002. The circuit 1070 also includes an inverter 1042, the input 1043 of which is coupled to the control input 1040 and the output 1044 of which is coupled to the second gate 1011 of the p-channel transistor 1001. When the pass gate 1000 is on, the output 1031 of the voltage source 1030 is coupled to the floating gate 122 to set or adjust the floating gate voltage VG. During a pH measurement period, the controller 180 turns off the pass gate 1000 to disconnect the voltage source 1030 from the floating gate 122.

[0059] Furthermore, in the illustrated example, the back gates or body connections of the transistors 1001 and 1002 of the pass gate 1000 are connected to the sources of the transistors 1001 and 1002. In the inactive state when the enable signal en = 0, the back gate interconnections create anti-parallel diodes that are configured to turn on when the floating gate voltage VG is different from the target voltage VTARGET. For the expected floating gate voltage variations of about + / - 10 mV for a delta temperature measurement, the resulting diode current is less than the leakage current for back gate connections to power and ground.

[0060] As described above in connection with Figure 2 Certain implementations include a plurality of sense transistors and associated fluid potential sensing portions 119. This facilitates simultaneous measurement of multiple sensors, for example, to reduce noise. In one example, the controller 180 obtains measurement sample signals from two fluid potential sensing circuits 140 coupled to respective sense transistors of the sensing portions 119. In one example, the controller 180 measures a first sensor at temperature T1 and a second sensor at temperature T2 in one measurement period, and then measures the second sensor at temperature T1 and the first sensor at temperature T2 in the next measurement period, to mitigate or eliminate the effects of noise and / or offset.

[0061] Some examples provide a reference-free pH sensor 100 that is cost-effective and low-complexity and operates at smaller signal levels than reference-based sensors. The described examples can implement fast sensing to collect additional data, thereby taking advantage of noise reduction techniques. Figure 1 and Figure 2 In the example of FIG, the sensing transistor 120 is laterally spaced apart from the metal resistor 154, and the temperature of the sensing transistor 120 is not strongly affected by the temperature variation of the heater. Figure 2 The multiple fluid potential sensing portions 119 shown in FIG. 1 allow for the use of matched reference transistors alongside the sense transistors to help compensate for local temperature differences caused by heating, even if the sense transistors 120 are not laterally spaced away from the metal resistors 154. In certain embodiments, layout configurations and architectures can be used to ensure that heat at the sense electrode 133 is minimally coupled to the sense transistors.

[0062] In one embodiment, the thermal effects can be mitigated by cooling the interconnection between the third electrode 133 and the floating gate 122, for example, by placing cold metal near the interconnect conductive structure or by routing the conductive interconnect structure over the polysilicon and / or field oxide of the semiconductor die outside the heater region, although extending the electrical interconnect may increase parasitic interconnect capacitance. The illustrated example includes a metal resistor 154 in the second level 107 of the metallization structure. In other examples, the semiconductor die includes a multi-layer metallization structure, for example, with heater metal at the PMD or polysilicon level, a first utilization level, a second metallization level, a third metallization level, etc., where the metal resistor 154 is preferably located near and below the sensing dielectric layer 113. Furthermore, the parasitic capacitance of the coupling between the metal resistor 154 and the sensing electrode 133 depends on the space between the two layers, and the coupling can be increased by making the dielectric layer 108 thicker or using multiple empty metal layers between the two layers.

[0063] In one example, the patterned electrode layer 110 is platinum or includes platinum. In operation, the potential of the fluid is set by contacting one of the plurality of electrodes of the patterned electrode layer 110, and the exposed electrode or electrodes are preferably or include a material that is non-reactive with the fluid, such as gold (Au), platinum (Pt), iridium (Ir), iridium oxide (IrOx), palladium (Pd), etc. The potential of the fluid 114 is ideally connected outside the heater area so that the voltage potential of the heated sensing electrode is not changed. Multiple electrodes contact the fluid 114 (e.g., as described above in Figure 1 、 2The ESD resistance of the fluid 114 is enhanced (as shown in FIGS. 8 and 8). Certain embodiments include an electrode located below the heater and close to the sense electrode 133 to facilitate improved ESD protection for the sensor 100. In one example, such an additional electrode is connected using an ESD cell such that for small voltages, the electrode is floating, but for large voltages is connected to ground in order to protect the floating gate 122 from ESD events. In certain examples, the signal level for sensing pH is relatively small because the sensor is measuring differences in relatively small temperature differences (e.g., 1 °C to 30 °C). For example, a 10 °C difference between T1 and T2 will generate approximately 5% of a signal at each pH compared to the signal generated by a sensor using an external reference.

[0064] In one example for sensing pH of the water fluid 114, the water has a built-in potential close to the floating gate dielectric layer 113 that should be stable. The water contacts the exposed portion of the platinum electrode (e.g., the upper portion of the Pt electrode 131 described above in Figure 8 , the services 111, 112, and 130), and the water potential is ideally stable. The contact between the water and the platinum generates a local potential between the water and the platinum. The water / Pt voltage drifts over time, but is stable for short times (e.g., in the range of seconds to minutes). Changing the Pt electrode potential will shift the water potential. In certain embodiments, the Pt electrode is also connected to the ESD circuit to protect the floating gate 122. The described examples facilitate pH measurements at different temperatures and can include separate temperature sensors and pH sensing regions with the same or similar layout (e.g., the comb / serpentine as shown above in Figure 2 ). Certain embodiments provide separate temperature sensors and pH sensing regions or areas (e.g., the temperature sensing regions 202 and 204, the fluid potential sensing regions 201 and 203, and the fluid potential sensing portions 119 above in Figure 2 ) with different layouts (e.g., serpentine and square) and a heater under each. Certain embodiments provide a combined pH sensing region and temperature sensor (e.g., parallel serpentine + comb). The use of controlled step signals applied to the end and center taps of the metal resistor structure mitigates or prevents heater power from changing the floating gate voltage VG. In addition, the described examples use orthogonal serpentine structures for heating and sensing (e.g., sensing temperature and pH) and a center tap driven differential heater to mitigate capacitive coupling between the heating device and the sensing electrodes. The comb structure of the electrodes 131 and 136 facilitates controlling the sensed fluid potential near the sensing electrodes, for example, using a comb structure interleaved with the sensing serpentine structure and the orthogonal heating structure. This allows for control of the sensed fluid potential as well as facilitating ESD protection of the floating gate 122.

[0065] Certain examples use short heater pulses, e.g., in the millisecond range, provided by the heater circuit 150 to facilitate fast sensing in conjunction with temperature control. Certain implementations also employ multiple pH sensors that are measured simultaneously, which can be independently heated to facilitate immunity to common mode noise signals, e.g., electrolyte potential, light, etc. Some examples also allow for substrate isolation at lower cost and higher flexibility. Furthermore, the isolation voltage capability of a given design can be varied by the layout across the semiconductor, e.g., trench width, while backside isolation can be varied by changing the thickness of the polymer. Capacitive connections are lower cost than standard connections using special metal / dielectric stacks for isolation through the wafer.

[0066] Modifications are possible in the described examples, and other implementations are possible.

Claims

1. A sensor comprising: a semiconductor die having a sensing side, a semiconductor substrate, a metallization structure, and a dielectric layer, the metallization structure including a first level on the semiconductor substrate and a second level between the first level and the sensing side, wherein the dielectric layer is between the sensing side and the second level; a transistor having a gate, a drain, and a source; a first electrode in the second level, the first electrode having a first surface exposed to the sensing side through a first opening in the dielectric layer; a second electrode in the second level, the second electrode being spaced apart from the first electrode and having a second surface exposed to the sensing side through a second opening in the dielectric layer; a third electrode in the second level, the third electrode being spaced apart from the first electrode and the second electrode, the third electrode being coupled to the gate, and the third electrode being separated from the sensing side by the dielectric layer; as well as A heater circuit has an output coupled to the metallization structure, wherein the heater circuit is configured to heat the sensing side via the metallization structure.

2. The sensor according to claim 1, further comprising: a fourth electrode in the second level, the fourth electrode being spaced apart from the first electrode, the second electrode, and the third electrode, and the fourth electrode being separated from the sensing side by the dielectric layer; and A temperature sensing circuit is coupled to the fourth electrode. 3 . The sensor of claim 2 , wherein the first electrode, the second electrode, the third electrode, and the fourth electrode comprise platinum.

4. The sensor according to claim 1, further comprising: a fluid potential sensing circuit having an input and an output, the input of the fluid potential sensing circuit being coupled to the transistor and the fluid potential sensing circuit being configured to provide an output signal at the output of the fluid potential sensing circuit; A controller having a controller input and a controller output, the controller input being coupled to the output of the fluid potential sensing circuit, and the controller being configured to provide a pH signal at the controller output in response to the output signal from the fluid potential sensing circuit.

5. The sensor according to claim 4, further comprising: A gate control circuit has an output coupled to the gate, wherein the gate control circuit is configured to provide an adjustment signal to the gate.

6. The sensor according to claim 5, wherein: the controller being coupled to the heater circuit; and The controller is configured to: controlling the heater circuit to refrain from heating the sensing side in a first mode, and receiving a first sample of the output signal from the fluid potential sensing circuit while the heater circuit refrains from heating the sensing side; in a second mode, controlling the heater circuit to heat the sensing side and receiving a second sample of the output signal from the fluid potential sensing circuit while the heater circuit heats the sensing side; and The pH signal is provided based on the first and second samples of the output signal from the fluid potential sensing circuit.

7. The sensor according to claim 6, further comprising: a fourth electrode in the second level, the fourth electrode being spaced apart from the first electrode, the second electrode, and the third electrode, and the fourth electrode being separated from the sensing side by the dielectric layer; as well as a temperature sensing circuit having an input coupled to the fourth electrode and a temperature sensing output; wherein the controller has a temperature sensing input coupled to the temperature sensing output and is configured to: receive a temperature feedback signal from the temperature sensing output in at least one of the first mode or the second mode; as well as The controller is configured to control the amplitude or timing of heating the sensing side based on the temperature feedback signal, or to control the sampling of the output signal from the fluid potential sensing circuit based on the temperature feedback signal, or to provide the pH signal based on the first sample and the second sample of the output signal from the fluid potential sensing circuit and the temperature feedback signal.

8. The sensor according to claim 1, further comprising: A gate control circuit has an output coupled to the gate, wherein the gate control circuit is configured to provide an adjustment signal to the gate.

9. The sensor of claim 8, wherein the gating circuit comprises: a first control transistor having a first control gate, a first control drain, and a first control source, the first control gate being coupled to the gate and the first control drain being coupled to a first voltage source; as well as A second control transistor has a second control gate, a second control drain, and a second control source, the second control gate being coupled to the gate and the second control drain being coupled to a second voltage source.

10. The sensor of claim 8, wherein the gating circuit comprises: Control input terminal; a transmission gate having a p-channel transistor and an n-channel transistor, wherein the p-channel transistor has a first gate, a first drain, a first source, and a first body connection; the n-channel transistor has a second gate, a second drain, a second source, and a second body connection; the second gate of the n-channel transistor is coupled to the control input; the first drain of the p-channel transistor is coupled to the gate; and the second drain of the n-channel transistor is coupled to the gate; a voltage source having an output terminal, the output terminal of the voltage source being coupled to the first source of the p-channel transistor and the second source of the n-channel transistor; as well as An inverter has an input coupled to the control input and an output coupled to the first gate of the p-channel transistor.

11. The sensor according to claim 1 , further comprising: a fourth electrode in the second level, the fourth electrode being spaced apart from the first electrode, the second electrode, and the third electrode, and the fourth electrode being separated from the sensing side by the dielectric layer; a temperature sensing circuit coupled to the fourth electrode; a fifth electrode in the second level, the fifth electrode being spaced apart from the first electrode, the second electrode, and the fourth electrode, the fifth electrode being separated from the sensing side by the dielectric layer, and the fifth electrode being coupled to the third electrode; as well as a sixth electrode in the second level, the sixth electrode being spaced apart from the first electrode, the second electrode, the third electrode, the fourth electrode, and the fifth electrode, and having a third surface exposed to the sensing side through a third opening in the dielectric layer; the fourth electrode and the fifth electrode having a serpentine shape with an elongated section extending in a first direction in the second level; The first electrode laterally surrounds the fourth electrode in the second level; The first electrode has an inwardly extending branch portion, the branch portion extending along the first direction between adjacent elongated sections of the fourth electrode; The sixth electrode laterally surrounds the fifth electrode in the second level; as well as The sixth electrode has an inwardly extending branch portion extending along the first direction between adjacent elongated segments of the first electrode.

12. The sensor according to claim 11, wherein: The first electrode and the fourth electrode are in a first region of the second level; The fifth electrode and the sixth electrode are in a second region of the second level, and the second region is spaced apart from the first region; as well as The second electrode laterally surrounds the first region and the second region.

13. The sensor according to claim 11, wherein: The metallization structure includes a metal resistor; The metal resistor includes a longitudinal segment; Each longitudinal segment has a respective first end and a second end and a respective tap between the first end and the second end; The longitudinal section extends along a second direction in the second level, and the second direction is orthogonal to the first direction; as well as the heater circuit comprising a first output coupled to a respective junction of the longitudinal segments, a second output coupled to the respective first ends of the longitudinal segments, and a third output coupled to the respective second ends of the longitudinal segments; and wherein the heater circuit is configured to: providing a first voltage signal at the second output terminal of the heater circuit that is positive relative to the voltage at the first output terminal of the heater circuit, and A second voltage signal that is negative relative to the voltage at the first output of the heater circuit is provided at the third output of the heater circuit.

14. A sensor comprising: A semiconductor die having a sensing side, a semiconductor substrate, a metallization structure, and a dielectric layer, the metallization structure comprising: a first electrode having a first surface exposed to the sensing side through a first opening in the dielectric layer; a second electrode having a second surface exposed to the sensing side through a second opening in the dielectric layer, the second electrode being spaced apart from the first electrode; and a third electrode spaced apart from the first electrode and the second electrode and separated from the sensing side by the dielectric layer; a transistor in the semiconductor die, the transistor having a gate, a drain, and a source, the gate coupled to the third electrode; a heater circuit configured to heat the sensing side; a fluid potential sensing circuit in the semiconductor die, the fluid potential sensing circuit coupled to the transistor and configured to provide a fluid potential output signal; and a controller in the semiconductor die, the controller coupled to the heater circuit and configured to: controlling the heater circuit to heat the sensing side at a first temperature; receiving a first sample of the fluid potential output signal from the fluid potential sensing circuit while the heater circuit heats the sensing side at the first temperature; controlling the heater circuit to heat the sensing side at a second temperature different from the first temperature; receiving a second sample of the fluid potential output signal from the fluid potential sensing circuit while the heater circuit is heating the sensing side at the second temperature; and A pH signal is provided based on the first sample and the second sample, the first temperature, and the second temperature.

15. The sensor according to claim 14, further comprising: a fourth electrode in the metallization structure, the fourth electrode being spaced apart from the first electrode, the second electrode, and the third electrode, and the fourth electrode being separated from the sensing side by the dielectric layer; as well as a temperature sensing circuit coupled to the fourth electrode; The controller is coupled to the temperature sensing circuit and is configured to verify or control the heater circuit to heat the temperature of the sensing side based on a temperature feedback signal from the temperature sensing circuit.

16. The sensor according to claim 15, further comprising: a gate control circuit having an output coupled to the gate, wherein the gate control circuit is configured to adjust a signal at the gate in response to a control signal from the controller; The controller is coupled to the gating circuit and is configured to provide the control signal to the gating circuit before or after the controller receives the first sample or the second sample of the fluid potential output signal from the fluid potential sensing circuit.

17. The sensor according to claim 14, further comprising: a gate control circuit having an output coupled to the gate, wherein the gate control circuit is configured to adjust a signal at the gate in response to a control signal from the controller; The controller is coupled to the gating circuit and is configured to provide the control signal to the gating circuit before or after the controller receives the first sample or the second sample of the fluid potential output signal from the fluid potential sensing circuit.

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