Optimization of pH sensing using silicon nanowire field effect transistors with HfO₂as the sensing surface

Abstract

Silicon nanowire field effect transistor sensors with SiO(2)/HfO(2) as the gate dielectric sensing surface are fabricated using a top down approach. These sensors are optimized for pH sensing with two key characteristics. First, the pH sensitivity is shown to be independent of buffer concentration. Second, the observed pH sensitivity is enhanced and is equal to the Nernst maximum sensitivity limit of 59 mV/pH with a corresponding subthreshold drain current change of ∼ 650%/pH. These two enhanced pH sensing characteristics are attributed to the use of HfO(2) as the sensing surface and an optimized fabrication process compatible with silicon processing technology.

Compact Model of a pH Sensor with Depletion-Mode Silicon-Nanowire Field-Effect Transistor

“…Ion-selective field-effect transistors (ISFETs) [1] using silicon nanowires (Si-NWs) have recently attracted considerable attention because they can be applied to many fields of healthcare and life sciences for label-free electrical detection of charged biological species such as pH levels, DNA, proteins, and other biomolecules [2][3][4][5][6][7]. Furthermore, the use of Si-NWs in pH sensors has been demonstrated in literature [2][3][4][5].…”

“…Furthermore, the use of Si-NWs in pH sensors has been demonstrated in literature [2][3][4][5]. A compact model for a Si-NW pH sensor has been reported to design and simulate a Si-NW pH sensor system that includes signal amplifying and processing circuits, [8].…”

“…A compact model for a Si-NW pH sensor has been reported to design and simulate a Si-NW pH sensor system that includes signal amplifying and processing circuits, [8]. A Si-NW fieldeffect transistor (SiNWFET) operating in the inversion mode in Si-NW pH sensors has been modeled [5,8], but most SiNWFETs have been operated in the depletion mode [2][3][4]. Therefore, a compact model of a depletionmode SiNWFET in the pH sensor needs to efficiently simulate the Si-NW pH sensor and SiNWFET-based integrated systems.…”

pH Response of Silicon Nanowire Sensors: Impact of Nanowire Width and Gate Oxide

“…(3)(4)(5)(6) The reduced size offers unique possibilities, such as the dense integration of multiplexed NWs, (7,8) which sense a large number of different target molecules simultaneously using differently functionalized NWs. (9) The key feature for biological applications is that nanostructures are on the scale of biological specimens.…”

“…Compared with SiO 2 , (4,10,11,16) these oxides provide a leakage-free (17) operation with an ideal Nernstian pH response that is independent of the salt concentration. (5,6,18) For the application of wide pH ranges, HfO 2 is a predestined candidate as a sensing surface due to its chemical inertness in most acidic or basic solutions.…”