A Review of Readout Circuit Schemes Using Silicon Nanowire Ion-Sensitive Field-Effect Transistors for pH-Sensing Applications

Abstract

This paper reviews various design approaches for sensing schemes that utilize silicon nanowire (SiNW) ion-sensitive field-effect transistors (ISFETs) for pH-sensing applications. SiNW ISFETs offer advantageous characteristics, including a high surface-to-volume ratio, fast response time, and suitability for integration with complementary metal oxide semiconductor (CMOS) technology. This review focuses on SiNW ISFET-based biosensors in three key aspects: (1) major fabrication processes and device structures; (2) theoretical analysis of key performance parameters in readout circuits such as sensitivity, linearity, noise immunity, and output range in different system configurations; and (3) an overview of existing readout circuits with quantitative evaluations of N-type and P-type current-mirror-based circuits, highlighting their strengths and limitations. Finally, this paper proposes a modified N-type readout scheme integrating an operational amplifier with a negative feedback network to overcome the low sensitivity of conventional N-type circuits. This design enhances gain control, linearity, and noise immunity while maintaining stability. These advancements are expected to contribute to the advancement of the current state-of-the-art SiNW ISFET-based readout circuits.

Keywords: N-type/P-type circuit; ion-sensitive field-effect transistor (ISFET); pH sensor; readout scheme; silicon nanowire (SiNW).

Figure A1

Small-signal model in (a) N-type readout circuit and (b) P-type readout circuit.

Figure 1

Trade-offs in semiconductor biochip design among linearity, dynamic (output) range, sensitivity (gain), noise, and headroom.

Figure 2

Relation between output and dynamic ranges with different headroom. Regions with solid lines denote available output ranges. (a) Narrower output and dynamic ranges due to small headroom; (b) wider output and dynamic ranges due to large headroom.

Figure 3

Trade-off between sensitivity and DR in biosensor design: (a) a narrower DR due to higher sensitivity; (b) a wider DR due to lower sensitivity. Regions with solid lines denote available output ranges.

Figure 4

Major fabrication process flow of integrated SiNW ISFET and CMOS devices. Reprinted with CC BY 2.0 from Ref. [116]. 2014, Jieun Lee.

Figure 5

(a) Top view of N- and P-type SiNW ISFETs. (b) Cross-sectional view of the SiNW ISFET. Adapted with permission from Ref. [97]. 2013, Jieun Lee.

Figure 6

${\mathrm{V}}_{\mathrm{TH}}$ shift with respect to pH changes in N-type and P-type SiNW ISFETs.

Figure 7

Transfer characteristics with respect to pH changes in (a) N-type and (b) P-type SiNW ISFETs.

Figure 8

Conventional [8] and sensitivity-enhanced [96] SiNW ISFET readout circuits.

Figure 9

SiNW/CMOS hybrid biosensor for signal amplification and noise suppression. Adapted with permission from Ref. [97]. 2013, Jieun Lee.

Figure 10

Complementary operation for signal amplification in the 1st stage. Adapted with permission from Ref. [97]. 2013, Jieun Lee.

Figure 11

(a) Voltage gain characteristics of the SiNW/CMOS hybrid biosensor. (b) Output voltage sensitivity comparison of three biosensor types (V_DD = 1.2 V). Adapted with permission from Ref. [97]. 2013, Jieun Lee.

Figure 12

Impact of noise at the output on the mapped input ranges with (a) a high sensitivity and (b) a low sensitivity. Red and blue lines show input and output noise, respectively.

Figure 13

(a) Schematic of an N-type. Adapted with permission from Ref. [98]. 2016, Seungguk Kim. (b) Schematic of a P-type readout circuit. Adapted with permission from Ref. [12]. 2019, Sungju Choi.

Figure 13

(a) Schematic of an N-type. Adapted with permission from Ref. [98]. 2016, Seungguk Kim. (b) Schematic of a P-type readout circuit. Adapted with permission from Ref. [12]. 2019, Sungju Choi.

Figure 14

Output range of (a) N-type and (b) P-type readout circuits.

Figure 15

Output voltage changes according to the pH concentration of the N-type readout circuit and the P-type readout circuit when R_out is set to 300, 400, and 500 kΩ.

Figure 16

(a) DNL and (b) INL of the N-type and P-type readout circuits with different ${\mathrm{R}}_{\mathrm{load}}$.

Figure 17

Bode plots of (a) N-type and (b) P-type readout circuits under different PVT conditions.

Figure 18

Output voltage variations due to the presence of supply noise in the (a) N-type readout circuit (temperature = −5 °C), (b) P-type readout circuit (temperature = −5 °C), (c) N-type readout circuit (temperature = 100 °C), (d) P-type readout circuit (temperature = 100 °C).

Figure 19

Schematic of the modified N-type readout circuit.

Figure 20

Simulated output voltages of the modified N-type readout circuit across varying pH concentrations and different R₂/R₁ ratios.

Figure 21

(a) Concept of supply noise immunity; (b) output voltage variations due to supply noise in the modified N-type readout circuits (temperature = −5 °C) (c) (temperature = 100 °C).

Figure 22

Bode plot of modified N-type readout circuits under different PVT conditions.