Surface Potential Visualization in Organic Antiambipolar Transistors Using Operando Kelvin Probe Force Microscopy for Understanding the Comprehensive Carrier Transport Mechanism

Abstract

which cannot be obtained by conventional Si-based electronics. [10][11][12][13][14][15] However, organic ICs suffer from difficulties in minimizing the individual transistors and memories owing to their incompatibility with conventional lithography techniques. Therefore, organic electronic circuits have poor dataprocessing capability and low-integration density. [1][2][3][4][5][6][7][8][9] Negative differential transconductance (NDT) is essential in developing epochmaking devices involving multivalued and reconfigurable logic circuits, which are expected to improve the data-processing capabilities and the integration density of current electronic devices. [16][17][18][19][20][21][22] However, the NDT properties have usually been observed in quantum-effect transistors, such as tunnel and single-carrier transistors. The stable operation of these devices is mostly limited at cryogenic temperatures. [19][20][21][22] Therefore, their practical applications remain far off. Recently, significant effort has been devoted to the evolution of antiambipolar transistors (AATs) with many kinds of materials, e.g., transition metal dichalcogenides, organic materials, and their hybrid systems. [23][24][25][26][27] An AAT is a heterojunction transistor type with a partially overlapped p-n junction in the transistor channel, which induces clear NDT properties at room temperature. Owing to the benefit of the stable NDT properties in the transistors, attractive logic circuits, including ternary and quaternary logic operations, have been demonstrated. [24][25][26] Among these efforts, we have developed AATs with organic semiconductors by taking advantages of the mechanical flexibility and simple formation process. [28][29][30][31][32][33][34][35] The combination of α-sexithiophene (α-6T) and N,N-dioctyl-3,4,9,10-erylenedicarboximide (PTCDI-C8) for p-and n-type semiconductors, respectively, exhibited high-gate tunability of the drain currents. [28][29][30][31][32] The ratio of the peak-and off-drain currents reached four orders of magnitude. Furthermore, the AAT enabled a ternary inverter by combining n-type transistors and electrically reconfigurable two-input logic circuits based on the dual-gate configuration. [31][32][33] Next, using organic semiconductors with higher carrier mobilities, such as 2,7-dioctyl[1]benzothieno [3,2-b][1]benzothiophene (C8-BTBT) and PhC 2 H 4 -benzo[de]isoquinolino [1,8gh]quinolone diimide (PhC 2 -BQQDI) for p-and n-type semiconductors, respectively, achieved extremely high peak-and offdrain current ratios (six orders of magnitude). [34] Moreover, we An antiambipolar transistor (AAT) exhibits a negative differential transconductance (NDT) due to a partially overlapped p-n junction formed in the transistor channel. However, the NDT origin remains unclear. In this study, the operando Kelvin probe force microscopy is employed to unveil this issue. When the AAT is turned on, steep potential drops induced by pinch-off states are visible in the p-and n-type channels. Due to the similarity to the surface potenti...

Reconfigurable Logic-in-Memory Constructed Using an Organic Antiambipolar Transistor

“…The equivalent circuit of the DG-OAAT is provided in Figure 1c, based on our previous studies. 39,45,46 First, we examined the operation of the BG transistor to confirm the carrier-trapping ability of the ZnPc-PS 4 layer for holes and electrons. Figure 1d shows a typical drain current (I D )−BG voltage (V G,bottom ) curve in the p-type operation of the DG-OAATs, where the drain voltage (V D ) and the TG voltage (V G,top ) were fixed at −14 and 0 V, respectively.…”

“…In our previous study, the Λ-shaped transfer curve of OAATs is explained by the same analogy with the shoot-through current in complementary metal-oxide semiconductor (CMOS) inverters. 45,46 Namely, the I D of the OAATs was given as the overlapped current of the constituent p-type and n-type transistors as defined by the following equations 45,46…”

“…We then considered the origin of the hysteresis in Λ-shaped transfer curves. In our previous study, the Λ-shaped transfer curve of OAATs is explained by the same analogy with the shoot-through current in complementary metal-oxide semiconductor (CMOS) inverters. , Namely, the I D of the OAATs was given as the overlapped current of the constituent p-type and n-type transistors as defined by the following equations , I normalD , normalp = prefix− W 2 L normalp μ normalp C normali , bottom false( V normalG , bottom − V th , normalp false) 2 goodbreak0em2em⁣ ( V G , bottom ≤ V peak ) I normalD , normaln = prefix− W 2 L normaln μ normaln C normali , bottom false( V normalG , bottom − V normalD − V th , normaln false) 2 goodbreak0em2em⁣ ( V G…”

“…On the basis of the above analyses, we summarize the relationship between the carrier transport process between the source and the drain electrode and the carrier-trapping and carrier-releasing processes in the nano - floating gate in Figure , where we consider the energy level alignments of the α-6T and PTCDI-C8 layers revealed by the operando photoelectron emission and Kelvin probe force microscopies. , The energy levels of the constituent materials are shown in Figure S3. First, we explain the carrier transport process between the source and the drain electrode (Figure a–c).…”

“…α-Sexithiophene (α-6T) and N , N ′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) films were used as p-type and n-type transistor channels, respectively. The film thicknesses were optimized to be 15 nm for the α-6T film and 8 nm for the PTCDI-C8 film to enhance the top-gate (TG) and bottom-gate (BG) tunability for both transistor channels. , A polymer layer, ZnPc-PS 4 , was inserted as a nano - floating gate between the organic channels and the BG insulator (HfO 2 ). The equivalent circuit of the DG-OAAT is provided in Figure c, based on our previous studies. ,, …”