Titanium Nitride-Based CMOS ION Image Sensor with 4.19-μM Resolution for Bioimaging

We report a titanium nitride (TiN)-based CMOS ion image sensor as a novel pH-sensitive membrane. TiN, which is widely used as a barrier metal in the interconnecting structures and compatible with CMOS process, has been demonstrated to achieve a near-theoretical sensitivity of 55 ± 3 mV/pH, matching the performance of conventional <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ta}_{2}\mathrm{O}_{5}$</tex> membranes. It enables two-dimensional real-time imaging of H<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> concentration without any labeling. The sensor exhibited high selectivity to interfering ions <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\text{Na}^{+}.\ \mathrm{K}^{+}.\ \text{Ca}^{2+})$</tex>. Furthermore, we successfully measured the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Na}^{+}, \mathrm{K}^{+}$</tex>, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ca}^{2+}$</tex> response by forming ion sensitive membrane on the pixel array, corresponding to the target molecule. Our novel imaging device represents a scalable and cost-efficient platform for future bioimaging applications.