Bio Organic-Semiconductor Field-Effect Transistor (BioFET) Based on Deoxyribonucleic Acid (DNA) Gate Dielectric

A nonvolatile memory device has a structure of a metal oxide semiconductor field effect transistor MOSFET where the conventional gate electrode is modified in a way to enable temporary charge storage inside the gate. The time when the stored charge decreases to 50 of its initial value is defined as retention time. A long retention time is required for nonvolatile memory devices. Using inorganic semiconductors like Si, this has been used in integrated circuits since the last four decades. Typically there are two types of nonvolatile memory devices, floating gate devices and metal-insulator-oxide-semiconductor MIOS devices. First attempts to use polarizable gate insulators in combination with organic semiconductors. The field effect transistors showed floating gate effects, but the potential for organic memories was not realized. Recently insulators based on polymeric ferroelectric-like materials were utilised to fabricate nonvolatile organic memory devices 18-21. One of the disadvantages of use of such polymeric ferroelectric-like materials is the very high surface roughness which does not allow forming smooth interface between insulator and organic semiconductor. As a result, on and off ratio and on current becomes extremely critical issue. We have demonstrated successfully a combination of a polymer space charge electret and an organic semiconductor in a field effect transistor configuration. Our initial experiments concerns with the study of the thin film morphology. Figure 5a shows the morphology of a 200 nm DNA-CTMA film spun on quartz substrate which resulted a surafe roughness of 10 nm. Features of self organised structures are observed. Fig. 5b shows the dielectric response C-V of the sandwiched DNA-CTMA film between the two electrodes MIM devices. It appears that DNA-CTMA film shows stable capacitance, C for a wide range of frequency with absolute capacitance of approx. 1.15 nFcm2.