An ion-gated bipolar amplifier for ion sensing with enhanced signal and improvednoise performance

• Published in: Applied physics letters 2014, Vol.105 (8), p.0821021
• Main Authors: Zhang, Da, Gao, Xindong, Chen, Si, Norström, Hans, Smith, Ulf, Solomon, Paul, Zhang, Shi-Li, Zhang, Zhen
• Format: Article
• Language: English
• Subjects: Engineering Science with specialization in Electronics; Ion-sensing; low frequency noise; signal to noise ratio; Teknisk fysik med inriktning mot elektronik
• ISSN: 1077-3118; 0003-6951
• DOI: 10.1063/1.4894240

This work presents a proof-of-concept ion-sensitive device operating in electrolytes. The device,i.e., an ion-gated bipolar amplifier (IGBA), consists of a modified ion-sensitive field-effect transistor(ISFET) intimately integrated with a vertical bipolar junction transistor for immediate currentamplification without introducing additional noise. With the current non-optimized design, theIGBA is already characterized by a 70-fold internal amplification of the ISFET output signal. Thissignal amplification is retained when the IGBA is used for monitoring pH variations. The tight integrationsignificantly suppresses the interference of the IGBA signal by external noise, which leadsto an improvement in signal-to-noise performance compared to its ISFET reference. The IGBAconcept is especially suitable for biochips with millions of electric sensors that are connected to peripheralreadout circuitry via extensive metallization which may in turn invite external interferencesleading to contamination of the signal before it reaches the first external amplification stage.