Research ArticleMATERIALS SCIENCE

Internal ion-gated organic electrochemical transistor: A building block for integrated bioelectronics

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Science Advances  27 Feb 2019:
Vol. 5, no. 2, eaau7378
DOI: 10.1126/sciadv.aau7378
  • Fig. 1 Structure and steady-state characteristics of IGT.

    (A) Schematic illustration of IGT cross section and wiring diagram for device operation (top). d-sorbitol creates an ion reservoir, maintaining mobile ions (green) that can travel within the channel; PEDOT-rich regions are shown in light blue and PSS lamellas in white (bottom). (B) Optical micrograph displaying the top view of an individual transistor. Scale bar, 20 μm. Inset shows a cross-sectional scanning electron microscopy (SEM) image acquired at a tilt angle of 30°. Ion membrane (light red), channel (light blue), and Au contacts for gate (G) and source (S; beige) are visible. Scale bar, 5 μm. Note that PEDOT:PSS coating of gate electrode is not visible in the image. (C) Output characteristics (IDVD) of IGT device (L = 5 μm, W = 500 μm) for gate voltage (VG) varying from 0 V (top curve) to +0.6 V (bottom curve) with a step of +0.1 V; color intensity corresponds to VG amplitude. (D) Transfer curve for VD = −0.6 V (black), and the corresponding transconductance (orange), |gmmax| = 32.30 mS.

  • Fig. 2 Internal mobile ions enable volume-based, fast, symmetric, and repetitive (de)doping of the conducting polymer channel.

    (A) Schematic cross-sectional illustration of IGT under normal operating conditions, with mobile ions maintained in the ion reservoir of the channel. (B) Schematic cross-sectional illustration of IGT at high gate voltage stress capable of forcing the ions to exit the channel and enter the ion membrane. Dashed red lines represent lower and upper bounds of VG during normal device operation. (C) Temporal response of the drain current (ID) highlighting a symmetrical rise (dedoping; gray boxed area 1) and fall (doping; gray boxed area 2) time of the drain current in response to pulsed gate voltage [VDS = −0.4, VGS pulse amplitude = 0.4 V (note that the device is turned off); bottom, L = 5 mm, W = 10 mm]. (D) Asymmetrical temporal response of the drain current (longer doping time; gray boxed area 2 compared to dedoping time in gray boxed area 1) resulting from longer ion transit distance [(VDS = −0.4, VGS pulse amplitude = 0.9 V; bottom, same device as (C)]. (E) Maximum transconductance of an IGT as a function of channel thickness (black) and gate area (orange); channel L = 5 mm, W = 10 mm. Transconductance was calculated from a transfer curve for VD = −0.6 V. (F) Maximum transconductance as a function of channel geometry. Transconductance was calculated for a 6 × 6 array of IGTs with logarithmically increasing channel length and width (fig. S1C) from a transfer curve for VD = −0.6 V.

  • Fig. 3 Contained mobile ions within the channel are necessary and sufficient for IGT operation.

    (A) Schematic cross-sectional illustration of IGT with contained mobile ions (top) versus OECT with external electrolyte (bottom). The IGT channel acts as ion reservoir, maintaining mobile ions in the vicinity of PSS anions, allowing faster (de)doping processes, whereas the OECT depends on diffusion of ions from an electrolyte into the channel. Note that the channels of both transistors contained sorbitol. (B) Temporal response of the drain current (ID) of an IGT (blue) and OECT (black) with the same dimension of channel (L = 30 μm, W = 12 μm, VGS pulse amplitude = 0.3 V). Exponential fit of the IGT drain current (red), resulting in a time constant of 31.7 μs, and of the OECT drain current (green), resulting in a time constant of 191.2 μs. (C) Schematic cross-sectional illustration of IGT with contained mobile ions (top) versus solid-state OECT with ions in a solid-state electrolyte layer (lower). (D) Normalized temporal response of the ID of an IGT (blue) versus the solid-state OECT (red) with the same dimension of channel (L = 5 mm, W = 10 mm); VG is shown in black. Inset magnifies the region of the response enclosed by the black dashed lines. IGT had a faster time response (τIGT = 46 ms) compared to the solid-state OECT (τOECT = 1.82 s). (E) Schematic cross-sectional illustration of a PEDOT:PSS (no mobile ions; top) and PEDOT:PSS + d-sorbitol (with mobile ions; bottom) channel devices, both with a SiO2 ion barrier layer. (F) Transfer curve for VD = −10 V of a PEDOT:PSS (red) versus PEDOT:PSS + d-sorbitol (blue) channel gated through a 90-nm-thick SiO2 layer; only the PEDOT:PSS + d-sorbitol device demonstrated modulation [same device geometry as (D)]. (G) Schematic cross-sectional illustration of IGT with contained mobile ions (top) versus deionized IGT (mobile ions removed from the channel; bottom). (H) Normalized transfer curve for VD = −0.5 V of the IGT with deionized channel (red) versus normal IGT (blue). a.u., arbitrary units.

  • Fig. 4 Contained mobile ions enable high-speed and wide-bandwidth IGTs.

    (A) Temporal response of the drain current (ID) of an IGT device with L = 12 μm and W = 5 μm. Exponential fit of the IGT drain current (red), resulting in a time constant of 2.6 μs (n = 512). (B) Small-signal peak-to-peak drain current (ID-PP) of an IGT operating at VD = −0.6 V and VG = 100 mV peak-to-peak sine wave, resulting in 380 kHz of effective bandwidth (∆IP-P was composed of the average of 10 cycles for each frequency).

  • Fig. 5 Integrated IGT-based digital logic gates and cascaded amplifiers.

    (A) IGT-based NAND and NOR gates conform to the surface of orchid petals (left). Scale bar, 1 cm. Optical micrographs of NOR (top right) and NAND (bottom right) logic gates. Input (I1 and I2) and output (O) configuration is indicated. Scale bar, 100 μm. (B) Temporal response of the output (O) drain current of a NOR (top) and a NAND (bottom) logic gate. First input signal (I1, blue), second input signal (I2, red), and output signal (O, black) are shown at the top. Dashed red lines mark the threshold of high and low logics. (C) Optical micrograph displaying the top view of an IGT-based cascaded amplifier. Scale bar, 20 μm. (D) Circuit diagram of IGT-based cascaded amplifier and the corresponding input and output signals. Input voltage, Vin, (red). Scale bar, 50 mV. Output signal from T1 (black). Final amplified output from T2 (blue). Scale bars, 50 μA and 100 ms. (Photo credit: Jennifer Gelinas, Columbia University)

  • Fig. 6 Micrometer-scale IGTs acquire high-quality human EEG signals.

    (A) Photograph of μ-EEG IGT (top left) and clinical EEG electrode (top right) mounted on the forehead of a healthy volunteer. Corresponding photograph after μ-EEG IGT and clinical EEG electrode were removed 1 hour later (bottom left and right); skin irritation was visible only in the vicinity of the clinical EEG electrode. (B) Optical micrograph of μ-EEG IGT conforming to human scalp; devices were designed to fit the interfollicular epidermis. Scale bar, 2 mm. (C) Wiring diagram of EEG recording using a μ-EEG IGT at VD = −0.6 V and VG = 0.4 V. Left frontopolar (FP1) and occipital (O1) regions were used for device placement. (D) Sample time trace of the signal recorded from O1 with μ-EEG IGT demonstrating alpha (α, blue), beta (β, yellow), and low gamma (γlow, green) oscillations (top). Time-frequency spectrogram of μ-EEG IGT recording demonstrating reactivity of posterior dominant rhythm to eye closure. Eye blink artifact is visible. Scale bar, 500 ms, 100 μV. Warmer colors represent higher relative power in in arbitrary units. (E) Comodulogram showing the cross-frequency coupling of the same recording epoch; significant coupling between α-β and β-γlow is indicated. (Photo credit: George Spyropoulos, Columbia University)

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/2/eaau7378/DC1

    Fig. S1. Fabrication process and IGT architecture.

    Fig. S2. PEDOT:PSS reduces the chitosan-Au electrochemical impedance at the IGT gate.

    Fig. S3. Comparison of electrochemical impedance of different material interfaces.

    Fig. S4. Comparison of ion species and ion membrane material on modulation magnitude and rise time of IGTs.

    Fig. S5. Internal mobile ions enable stable operation over time without a decrement in speed or significant drift in drain current.

    Fig. S6. Effect of channel geometry on IGT Ion/Ioff.

    Fig. S7. Output characteristics of IGT and OECT devices with identical geometry.

    Fig. S8. Output characteristics of IGT and SS-OECT devices with identical geometry.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Fabrication process and IGT architecture.
    • Fig. S2. PEDOT:PSS reduces the chitosan-Au electrochemical impedance at the IGT gate.
    • Fig. S3. Comparison of electrochemical impedance of different material interfaces.
    • Fig. S4. Comparison of ion species and ion membrane material on modulation magnitude and rise time of IGTs.
    • Fig. S5. Internal mobile ions enable stable operation over time without a decrement in speed or significant drift in drain current.
    • Fig. S6. Effect of channel geometry on IGT Ion/Ioff.
    • Fig. S7. Output characteristics of IGT and OECT devices with identical geometry.
    • Fig. S8. Output characteristics of IGT and SS-OECT devices with identical geometry.

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