Bipolar junction transistor (BJT) for liquid flow biosensing applications without a reference electrode and large sensing area

A sensor comprising:

• a sample trench;
• a first bipolar junction transistor doped to a first conductivity type having a first sensing surface of a first extrinsic base region providing a first sidewall of the sample trench;
• and
• a second bipolar junction transistor doped to a second conductivity type having a second sensing surface of a second extrinsic base region providing a second sidewall of the sample trench.

A method of forming a sensor comprising:

• forming a bipolar junction transistor including a base region, and a two-component extrinsic base region;
• forming a sample trench exposing a sidewall of a first component of the two-component extrinsic base region;
• and
• forming a sensor surface on the sidewall of the first component of the extrinsic base region that is opposite a sidewall of the first component of the extrinsic base region that is in contact with the base region.