Ion sensing device

An ion sensing device comprising:

• a first field-effect transistor;
• a second field-effect transistor;
• a reference electrode configured to directly contact a sample solution;
• a first ion-sensitive film;
• and
• a second ion-sensitive film,
• wherein each of the first field-effect transistor and the second field-effect transistor includes:
• a semiconductor film;
• a bottom gate electrode;
• a bottom gate insulating film located between the bottom gate electrode and the semiconductor film;
• and
• a top gate insulating film,
• wherein the first ion-sensitive film is configured to generate a top gate potential with respect to the semiconductor film of the first field-effect transistor in accordance with an ion concentration of the sample solution when being in direct contact with a sample solution,
• wherein the second ion-sensitive film is configured to generate a top gate potential with respect to the semiconductor film of the second field-effect transistor in accordance with the ion concentration of the sample solution when being in direct contact with the sample solution,
• wherein a potential of the reference electrode is supplied to a source/drain of the semiconductor film of each of the first field-effect transistor and the second field-effect transistor,
• wherein surface materials in contact with the sample solution for the first ion-sensitive film and the second ion-sensitive films are the same, and
• wherein a sensitivity of the combination of the first field-effect transistor and the first ion-sensitive film is higher than a sensitivity of the combination of the second field-effect transistor and the second ion-sensitive film.