Active chemically-sensitive sensors with in-sensor current sources
View Patent ↗Methods and apparatus relating to FET arrays for monitoring chemical and/or biological reactions such as nucleic acid sequencing-by-synthesis reactions. Some methods provided herein relate to improving signal (and also signal to noise ratio) from released hydrogen ions during nucleic acid sequencing reactions.
1. An apparatus comprising an array of sensors, a sensor in the array comprising:
a chemically-sensitive field effect transistor (chemFET) having a first conduction terminal, a second conduction terminal coupled to a first supply voltage conductor, and a sensor surface;
a first transistor having a first conduction terminal directly coupled to the first conduction terminal of the chemFET, a second conduction terminal coupled to a second supply voltage conductor, and a gate coupled to a bias voltage conductor;
a second transistor having a gate directly coupled to the first conduction terminal of the chemFET, a first conduction terminal coupled to a third supply voltage conductor, and a second conduction terminal; and
a third transistor having a gate coupled to a select signal conductor, a first conduction terminal coupled to the second conduction terminal of the second transistor, and a second conduction terminal coupled to an output conductor.
2. The apparatus of claim 1 , wherein the bias voltage conductor is coupled to a bias voltage source having a level setting the first transistor in a sub-threshold mode.
3. The apparatus of claim 1 , wherein the bias voltage conductor is coupled to a bias voltage source having a level setting the first transistor in a reverse-biased diode mode.
4. The apparatus of claim 1 , wherein the first supply voltage conductor is coupled to ground, the second supply voltage conductor is coupled to a positive supply voltage and the third supply voltage conductor is coupled to the positive supply voltage.
5. The apparatus of claim 1 , wherein the output conductor is a column bus, and the select signal conductor is a row select signal conductor.
6. The apparatus of claim 1 , wherein a voltage on the output conductor is a function of a threshold voltage of the chemFET.
7. The apparatus of claim 6 , wherein the threshold voltage of the chemFET is based on an ion-concentration of an analyte solution coupled to the sensor surface of the chemFET.
8. The apparatus of claim 1 , wherein the chemFET includes a floating gate and a passivation layer on the floating gate, and the sensor surface is a surface of the passivation layer over the floating gate.
9. The apparatus of claim 8 , wherein a voltage on the output conductor indicates an ion-concentration of an analyte solution coupled to the floating gate via the passivation layer.
10. The apparatus of claim 1 , including a chemical sample well including the sensor surface of the chemFET, and a reference electrode coupled to an analyte solution in fluid flow communication with the chemical sample well.
11. The apparatus of claim 1 , wherein a sensor in the array consists of the chemFET, the first transistor, the second transistor and the third transistor, and corresponding conductors.
12. The apparatus of claim 1 , wherein the first transistor is a current source to provide a bias current to the chemFET.
13. The apparatus of claim 12 , wherein the bias current establishes a voltage on the first conduction terminal of the chemFET based on a threshold voltage of the chemFET.