A CMOS-Compatible, Low-Noise ISFET Based on High Efficiency Ion-Modulated Lateral-Bipolar Conduction

Abstract

Ion-sensitive, field-effect transistors (ISFET) have been useful biosensors in many applications. However, the signal-to-noise ratio of the ISFET is limited by its intrinsic, low-frequency noise. This paper presents an ISFET capable of utilizing lateral-bipolar conduction to reduce low-frequency noise. With a particular layout design, the conduction efficiency is further enhanced. Moreover, the ISFET is compatible with the standard CMOS technology. All materials above the gate-oxide are removed by simple, die-level post-CMOS process, allowing ions to modulate the lateral-bipolar current directly. By varying the gate-to-bulk voltage, the operation mode of the ISFET is controlled effectively, so is the noise performance measured and compared. Finally, the biasing conditions preferable for different low-noise applications are identified. Under the identified biasing condition, the signal-to-noise ratio of the ISFET as a pH sensor is proved to be improved by more than five times.

An ultrasensitive method of real time pH monitoring with complementary metal oxide semiconductor image sensor

“…CMOS image sensor based pH analysis is the very simple and rapid method. Small drops of different pH level (pH [1][2][3][4][5][6][7][8][9][10][11][12][13][14] solutions were applied to the 14 individual hydrogel films. After few seconds, hydrogel absorbed the solutions and developed the color based on the pH range.…”

“…However, the total response time is little longer for real time application. Further, MEMS based pH sensing systems such as ion sensitive field-effect transistor (ISFET) [6], complementary metal oxide semiconductor (CMOS) based pH imager [7], optical fiber [8], magnetoelastic [9], conductometric [10], cantilever [11], fluorescent pH sensor [12] and potentiometric pH sensors [13] have constructed based on the requirement and applications. These kinds of sensors are capable of applying in various fields of chemical, biological, clinical, ecology, etc., as a real time pH sensor.…”

Comparison of the Extended Gate Field-Effect Transistor with Direct Potentiometric Sensing for Super-Nernstian InN/InGaN Quantum Dots

“…Although extensively discussed in dedicated studies, the OCP and EGFET readout modes including noise were barely compared directly and judged for their superiority. 22 , 23 …”

“…Although extensively discussed in dedicated studies, the OCP and EGFET readout modes including noise were barely compared directly and judged for their superiority. 22,23 Super-Nernstian InN/InGaN quantum dot (QD) potentiometric biosensors, functionalized for the selective detection of glucose and cholesterol, and anion-selective potentiometric sensors have been reported before. 24−26 Here, we study the EGFET sensor readout in the linear and saturated regime of an InN/InGaN QD electrode with super-Nernstian response grown on a Si(111) substrate and compare it with the direct OCP readout to elucidate the optimum performance.…”

“…W is the gate width, L is the gate length, μ e is the electron mobility for an n-channel FET, and C ox is the areal gate capacitance. Although extensively discussed in dedicated studies, the OCP and EGFET readout modes including noise were barely compared directly and judged for their superiority. , …”