Kwang Soup Song

Cl− sensitive biosensor used electrolyte-solution-gate diamond FETs

We have investigated the electrolyte-solution-gate field effect transisitors (SGFETs) used hydrogen terminated (H-terminated) or partially oxygen terminated (O-terminated) polycrystalline diamond surface in the Cl- and Br- ionic solutions. The H-terminated channel SGFETs are insensitive to pH values in electrolyte solutions. The threshold voltages of the diamond SGFETs shift according to the density of Cl- and Br- ions about 30 mV/decade. One of the attractive biomedical applications for the Cl- sensitive SGFETs is the detection of chloride density in blood or in sweat especially in the case of cystic fibrosis. The sensitivities of Cl- and Br- ions have been lost on the partially O-terminated diamond surface. These phenomena can be explained by the polarity of surface change on the H-terminated and the O-terminated surface.

Surface-modified Diamond Field-effect Transistors for Enzyme-immobilized Biosensors

The enzyme sensors using electrolyte-solution-gate diamond field effect transistors (SGFETs) have been developed for the first time. The hydrogen-terminated surface channel of the FETs was modified into partially aminated and oxygen-terminated (H-A-O-terminated) with irradiation of ultraviolet in an ammonia environment. The pH response of that is obtained about 50 mV/pH at pH 2–10. The concentration of substrates (urea or glucose) in the electrolyte solution has been detected by the pH change due to the bio-catalyzed effect of enzyme (urease or glucose oxidase), which is immobilized on the channel of SGFETs. The sensitivity of urea and glucose is approximately 30 mV/decade and 20 mV/decade respectively.

Effect of iodide ions on the hydrogen-terminated and partially oxygen-terminated diamond surface

Abstract The effect of I − ions on the threshold voltages of the electrolyte-solution-gate diamond field-effect transistors (SGFETs) in KI solution is investigated. The threshold voltages of hydrogen-terminated (H-terminated) diamond SGFETs shift in the KI concentration range of 10 −6 –10 −1 M in aqueous solutions. The sensitivity of the H-terminated diamond surface to I − ions is higher than that to Cl − or Br − ions. However, the sensitivity to I − ions of the partially oxygen-terminated (O-terminated) diamond surface drastically decreases with ozone treatment. The mechanisms of these phenomena can be explained by the surface charge and the adsorbability of I − ions on the H-terminated and O-terminated diamond surfaces.

Miniaturized diamond field-effect transistors for application in biosensors in electrolyte solution

The authors fabricated diamond solution-gate field-effect transistors (SGFETs) with miniaturization of the channel length to 5μm by photolithography. The channel surface was directly functionalized with amine by ultraviolet irradiation in an ammonia gas for 4h and aminated diamond SGFETs were sensitive to pH by 40mV∕pH. Urease was immobilized on the amine-modified channel surface, which was sensitive to urea by 27μA/decade from 10−5M to 10−2M. The authors fabricated submicron-sized (500nm) diamond SGFETs using electron-beam lithography. The transconductance (gm) was 56mS∕mm, which was 930-fold greater than that of the 500μm channel length.

Characterization of direct immobilized probe DNA on partially functionalized diamond solution-gate field-effect transistors

Amino groups were functionalized directly on the diamond surface after treating 0.5 monolayer of oxidation for detection of DNAs. Also, immobilization of probe DNAs was carried out directly on the partially aminated diamond without linker molecules. Specific hybridization with 21-mer DNA at a concentration of 100 nM could be clearly detected by two methods, fluorescence microscopy and diamond solution-gate field-effect transistors (SGFETs). DNA hybridization was confirmed using Cy-5-labeled target DNA on a micropatterned diamond surface. The changes in gate potential by the negative charge of immobilized or hybridized DNA were measured on SGFETs and hybridization efficiency on the functionalized diamond surface was estimated as about 40%.

RF diamond transistors : Current status and future prospects

RF diamond transistors have been developed on a hydrogen-terminated surface conductive layer. fT and fmax of 23 and 25 GHz, respectively, have been achieved in a diamond MISFET with a 0.2 µm gate length. Utilizing de-embedding and small-signal equivalent circuit analysis, parasitic components are extracted. The intrinsic fT and fmax of the 0.2-µm-gate diamond MISFET are estimated to be 26 and 36 GHz, respectively. In this report, some of the challenging steps in device fabrication processes such as the development of a low-resistivity ohmic layer, a high-quality gate insulator and acceptor density control technology, toward high-power and high-frequency diamond transistors with high reliability, are introduced.

Characterization of Hybridization on Diamond Solution-Gate Field-Effect Transistors for Detecting Single Mismatched Oligonucleotides

Using diamond field-effect transistors (FETs) operated in electrolyte solution (solution-gate FETs; SGFETs), a label-free charge detection method between complementary and single mismatched target oligonucleotides is proposed. The probe oligonucleotides immobilized at the activated carboxyl groups of carboxylic aromatic compounds (CACs) on the previously formed amino groups of the diamond surface. The high performance of the diamond surface for oligonucleotides detection was studied with respect to selectivity, sensitivity, and reproducibility of the diamond SGFETs.

Cryogenic operation of surface-channel diamond field-effect transistors

Abstract Cryogenic operation of field-effect transistors (FETs) fabricated on hydrogen-terminated (H-terminated) diamond surface conductive layers is investigated. 5-μm gate-length metal-insulator-semiconductor FETs (MISFETs) is fabricated using CaF2 film as a gate insulator. The MISFETs operate successfully even at 4.4 K. At low temperature, the contact between source/drain electrode and H-terminated diamond surface cannot maintain ohmic characteristics, because the thermal activation energy of the carriers is not high enough to overcome the barrier height at the interfaces between the source electrode and the H-terminated diamond. Estimated channel mobility increases from 63 cm2/V-s to 137 cm2/V-s and the maximum transconductance increases from 10.5 mS/mm to 14.5 mS/mm, as the temperature decreases from 300 K to 4.4 K, indicating reduced phonon scattering of the channel.

Direct immobilization of DNA on partially functionalized diamond surface

Amino groups were functionalized directly on the diamond surface after treating oxidation and fluorination for detection of DNAs, respectively. For simple process, immobilization of probe DNAs was carried out directly on the partially aminated diamond without linker molecules. After fabricating micropatterned diamond, specific hybridization with Cy-5 labeled target DNA at a concentration of 100 nM could be clearly detected on H-terminated, partially O-terminated, and partially F-terminated diamonds, respectively. The hybridization intensities determined by epifluorescence microscopy were compared and analyzed.