All‐Carbon‐Based Complementary Integrated Circuits

Owing to the growing global increase in electronic and electrical waste (e‐waste), significant challenges arise regarding the proper disposal of electronic devices. One potential solution that has gained attention is the development of disposable electronics, in which all components are designed to be for safe and environmentally friendly disposal. In this study, all‐carbon‐based complementary integrated circuits composed of printed single‐crystalline thin films of p‐ and n‐type organic semiconductors, graphite‐based carbon electrodes/wiring, and polymeric dielectrics/substrates are demonstrated. Elemental analysis reveals that the total amount of metallic element contaminants weighed <50 parts per million (ppm). The demonstrated analog/digital integrated circuits with 64 p‐ and n‐type organic thin‐film transistors exhibit stable operation under ambient environmental conditions. These all‐carbon‐based complementary integrated circuits possess excellent element traceability, thus mitigating the potential environmental impacts throughout the device's life cycle. Consequently, this advancement represents a significant step toward addressing the global environmental challenges associated with e‐waste.


Introduction
The rapid expansion of applications driven by the imminent Internet of Things (IoT) [1] and smart packaging [2,3] has created a growing demand for electronic devices.However, these devices have a significantly shorter lifespan, lasting only days instead of years.This raises concerns about how these electronic components are disposed of and the extent to which they are recycled.The challenges associated with electronic and electrical waste (e-waste), which includes unused, non-functional, or endof-life electronic components, have been ongoing since the 1970s. [4,5]Typical electronic components not only contain toxic elements or hazardous substances such as heavy metals (lead, mercury, and cadmium) [4] or brominated flame retardants, [5] but also noble metals such as gold.Consequently, there is an urgent need to develop functional materials and processes that can balance the device performance, manufacturability, cost, and sustainability.
Research on disposable electronics has primarily focused on carbon-based electronic technologies. [6]Especially all-carbonbased electronics, when completely incinerated, do not leave behind hazardous residues containing inorganics or heavy metals, thereby alleviating concerns about environmental pollution.Hence replacement of typical electronics with all-carbonbased ones can reduce the total amount of e-waste that is difficult to dispose of or recycle.Furthermore, all-carbon-based electronics are fundamentally composed of universally available carbon, without utilizing precious resources such as noble metals or rare earths that are concerned with future depletion.Therefore, electronic components composed purely of carbon-based materials can be expected to meet their end of life with complete combustion, free from recycling requiring extra costs.With these advantages, all-carbon-based electronics can contribute to achieving a sustainable IoT society in future.Regarding their components, carbon nanotubes (CNTs) [7] and -conjugated organic semiconductors (OSCs) [8][9][10] have been explored as potential active semiconductors.Various functional polymers, such as polyimide (PI), [11] poly(methyl methacrylate) (PMMA), [11] parylene, [11] shellac, [12] cellulose, [13][14][15] and polylactic acid, [16] have been used as dielectric materials and substrates. [8,9]Additionally, conductive polymers, [17] graphite/carbon black, [18][19][20] and graphene [21][22][23] have shown the ability to replace noble metal electrodes. [8]While individual transistors/sensors made of carbon-based materials have been demonstrated, practical methods for integrating these components into complementary electronic circuits remain limited.Furthermore, to the best of our knowledge, no previous study has thoroughly assessed the constituent elements of carbon-based electronics.
In this study, our objective was to create disposable electronics by fabricating all-carbon-based complementary integrated circuits on a PI film.We achieved this by combining printed singlecrystalline OSCs, graphite-based carbon electrodes/wiring, and polymeric dielectrics/substrates without the use of any metals.Elemental analysis confirmed the presence of only trace amounts of metallic elements, with the total amount of metallic element contaminants weighing <50 ppm.We successfully demonstrated the stable operation of various analog/digital circuits, including an inverter, ring oscillator (RO), 4 × 1 multiplexer (MUX), and D flip-flop (DFF), at a supply voltage (V dd ) of 10 V in air.Furthermore, we operated the 4 × 1 MUX by utilizing the two DFFs as a 2-bit Gray code counter and the RO as a clock generator.Interconnecting these circuits resulted in a fully functional 4bit ID output device.The proposed materials and their fabrication techniques pave the way for future disposable electronics and contribute to resolving global environmental issues related to e-waste.

Film Device Fabrication
We fabricated prototypes of all-carbon-based complementary integrated circuits as film devices by combining p-and n-type single-crystalline OSCs, carbon electrodes, carbon wiring, and an insulating organic polymer on a PI film substrate.The fabrication process involved several steps (also referred to as the inverter process in Figure 1a): First, a layer of graphitelike carbon with a thickness of 30 nm was deposited on a 100 mm × 100 mm PI film substrate using an e-beam evaporator at a deposition rate of 0.3-0.5 Å s −1 .The deposited carbon was then patterned using a photolithographic lift-off process, resulting in the formation of gate electrodes and conductive carbon wiring.Figure 1b shows the images of the patterned carbon on the PI film, which was successfully formed across the entire substrate at the minimum resolution of line/space (L/S) = 30 μm/10 μm.The roughness of the graphite-like carbon was evaluated using atomic force microscopy (AFM), as shown in Figure 1c, revealing a smooth surface with a Gaussian-distributed roughness characterized by a root-mean-square (RMS) roughness of S q = 0.56 nm.This level of smoothness was sufficient for stacking subsequent layers without any unevenness.In addition, as a result of the 4-terminal sensing, the sheet resistance and volume resistivity of the graphite-like carbon film were 7.04 × 10 3 Ω sq −1 and 2.11 × 10 −2 Ω⋅cm, respectively (see Table S1 and Figure S1a, Supporting Information).Although the resistivity is relatively higher than that of commonly used metals, this sheet resistance is significantly lower by more than three orders of magnitude compared to that of the OSCs in their ON-state, demonstrating that the carbon film serves as sufficiently low-resistance electrodes and wiring for the circuits.
Finally, in the fourth step, carbon contact electrodes with a thickness of 60-80 μm were deposited on both OSCs by spraying an XC-9089 carbon suspension through a stainless-steel stencil mask.This process allowed us to obtain complementary integrated circuits consisting of p-and n-type all-carbon-based organic thin-film transistors (OTFTs).Figure 1d shows a schematic of the spraying process, where the carbon suspension is transformed into a fine mist through the flow of atomizing gas and patterned based on the openings in the stencil mask.The channel length and width (L/W) were fixed at 100 μm/70 μm for the ptype OTFTs and 100 μm/300 μm for the n-type OTFTs, except for those in the RO.Note that the sheet resistance and volume resistivity of the sprayed carbon were evaluated to be 1.34 × 10 3 Ω sq −1 and 9.37 Ω⋅cm, respectively, using the 4-terminal sensing method (see Table S1 and Figure S1b, Supporting Information).This result also indicates that the sheet resistance of the sprayed carbon, similar to the graphite-like carbon film, is significantly lower compared to that of the OSCs in their ON-state.For a detailed description of the procedure, please refer to Experimental Section.The circuit represents a complementary inverter and its four electrical terminals.First, graphite-like carbon (t = 30 nm) was patterned onto the PI film substrate to form carbon gate electrodes and wiring, and then encapsulated with parylene diX-SR (t = 200 nm) as a gate insulator.Next, the single-crystalline thin films of the OSCs were transferred onto the insulator surface, and subsequently via holes were laser-drilled through the insulator.Finally, carbon contact electrodes were formed by spraying an XC-9089 carbon suspension.b) A photo image of the e-beam deposited graphite-like carbon (t = 30 nm) on a 100 mm × 100 mm PI film substrate that was photolithographically patterned at a micrometer scale.The inset shows a microscopic image of the patterned carbon with the resolution of line/space (L/S) = 30 μm/10 μm.c) An atomic force microscopy (AFM) image of a surface of the e-beam deposited graphite-like carbon in the area of 5 μm × 5 μm.The height distribution reveals a smooth surface with a Gaussian-distributed roughness characterized by a root-mean-square (RMS) roughness of S q = 0.56 nm.d) A schematic of the spraying process to form the carbon contact electrodes on the OSCs, where an XC-9089 carbon suspension is transformed into a fine mist through the flow of atomizing gas and patterned on the PI film substrate based on the openings in the stencil mask.

Characteristics of p-and n-Type OTFTs and Their Complementary Inverter
Complementary circuits, which consist of pairs of p-and n-type transistors arranged in a complementary manner, play a crucial role in the development of high-performance electronic devices.These circuits serve as fundamental building blocks in modern electronics because of their low power consumption and high noise immunity.Therefore, it is worthwhile to investigate the characteristics of p-and n-type all-carbon-based OTFTs, as well as their simple complementary circuit, which is an inverter.
We evaluated the electrical characteristics of the OTFTs and inverter in air under dark conditions.Figure 2a-f shows the polarized optical microscopy (POM) images and transistor char-acteristics of the p-and n-type OTFTs.The transfer curves in the saturation regime and the output curves exhibit negligible hysteresis and a high on-off current ratio of 10 7 , which is textbook-like behavior, as previously reported for OTFTs with carbon contact electrodes. [18]The threshold (V th ) and turn-on (V on ) voltages were determined as −0.05 and 0.00 V for the ptype OTFT and +2.40 and 0.00 V for the n-type OTFT, respectively, indicating that the complementary circuit consisting of these OTFTs can operate with relatively small voltage.The effective field-effect mobilities of holes (μ h,eff ) and electrons (μ e,eff ) extracted from the transfer curves in the saturation regime were evaluated to be μ h,eff = 2.86 cm 2 V −1 s −1 for the p-type OTFT and μ e,eff = 0.65 cm 2 V −1 s −1 for the n-type OTFT.Hence, their ONstate current values matched reasonably well when the channel  width ratio of the p-and n-type OTFTs (W p :W n ) was adjusted to 70:300.This enables the complementary circuit to operate properly and minimizes power consumption.
We demonstrate an all-carbon-based inverter consisting of one p-and one n-type OTFTs as the simplest complementary circuit.Figure 2g shows the POM images where the aforementioned p-and n-type OTFTs are connected, as depicted in the circuit diagram in Figure 2h.As expected from the individual transistor characteristics, the inverter operated properly at different V dd values ranging from 5 to 30 V, as shown in the voltage transfer curves (VTCs) in Figure 2i.Notably, the inverter operates at the relatively low V dd = 5 V, along with a low power consumption of 18 nW.Furthermore, all VTCs were symmetric; that is, the switching voltage V sw corresponding to the point on the VTC where V out = V in (V out : output voltage, V in : input voltage), was almost half the value of the applied V dd .Symmetric VTCs indicate that the circuit has an overall noise immunity owing to the relatively large noise margin, which contributes to reliable circuit operation by both increasing and decreasing V in .The maximum values of the signal gain (gain = ∂V out /∂V in ) fell between 11 and 16 at approximately V sw .Therefore, it should be emphasized that an all-carbon-based complementary circuit is stably operable.All characteristics are summarized in Table S2 (Supporting Information).

Elemental Composition and Metal Content
In the proposed fabrication process, we have successfully removed any metal elements from the device components.How-ever, there is a possibility that small amounts of metal elements have been accidentally contaminated due to impurities present in the raw materials, for example catalysts, and have contributed to the performance of the device.In addition, for some commercially available materials, details of the raw materials are not disclosed.To dispel this concern, we quantitatively investigated the elemental composition of a PI film-based all-carbon circuit, specifically a film device.This investigation utilized two analytical methodologies: elemental analysis and inductively coupled plasma mass spectrometry (ICP-MS).Traditional elemental analysis typically requires samples weighing a few tens of milligrams, which can be challenging to obtain using conventional methods.However, our scalable device manufacturing process, which allows for area up to the cm 2 range, facilitated the acquisition of a sufficient number of film devices.Elemental analysis of carbon (C), hydrogen (H), nitrogen (N), sulfur (S), and halogens (F, Cl, and Br) revealed that this film device was composed of C (69.95%), H (2.34%), N (9.23%), S (0.12%), and Cl (0.56%), whereas F and Br were not detected (Figure 3a; Table S3, Supporting Information).Comparing these findings with the expected values calculated from the weight ratio of each component, including the PI substrate, parylene insulator, OSCs, and carbon electrodes, we determined that 17.80% of the unknown composition was derived from oxygen (O).In this calculation, we assumed typical chemical structures for PI and parylene since their accurate structures are industrially confidential.These results indicate that the film device solely consists of carbon-based materials, encompassing organic compounds and inorganic carbon.To gather further information regarding the elemental composition, we investigated the content of 61 metallic elements in the film device, specifically all naturally occurring nonradioactive metallic elements, using ICP-MS.This technique enables simultaneous detection of multiple elements with high sensitivity in the ppb-ppt range. [27]Due to its rapid and comprehensive analysis capabilities, ICP-MS is well-suited for trace-element detection and can assess the elemental composition of contaminants unintentionally introduced into the film device.Following the procedure outlined in Experimental Section, we completely digested 13.43 mg of the film device in an acidic mixture of 60% HNO 3 /96% H 2 SO 4 /60% HClO 4 (3:5:2 v/v/v) using microwave irradiation, resulting in 13.66 g of a pale-yellow transparent solution.The metal content of the film device was determined from the qualitative and quantitative analyses of this solution.While the contents of most metallic elements were below the limit of detection (LOD), such as 35 ppm for Ca, 10 ppm for K, 7 ppm for Fe, and <0.5 ppm for the other metal elements, eight metals (Li, Na, Cu, Zn, Rb, Sr, Cs, and Ba) were identified through qualitative analysis, allowing for their quantitative determination.As shown in Figure 3b (see also Table S4, Supporting Information), the most abundant metal in the film device was found to be Zn (32.3 ppm), followed by Na (2.5 ppm).The contents of the remaining six metals were 2.0 ppm or lower.The presence of trace amounts of metallic elements, measuring <50 ppm by weight, strongly suggests that the film device is free of metals in terms of elemental composition.

Analog Circuit: Ring Oscillator
Analog circuits play a vital role in electrical and computational engineering as they enable the processing and manipulation of continuous-time signals.In this study, we fabricated an allcarbon-based 5-stage RO on a PI film by connecting five inverters in a closed loop with an additional inverter at the output terminal, as depicted in the circuit diagram in Figure 4a.As shown in the microscopic image in Figure 4b, the inverters in the loop consist of OTFTs with a tenfold longer channel length of L = 1000 μm to increase the delay time, whereas the additional inverter for output waveform shaping consists of OTFTs with a typical channel length of L = 100 μm.Most of the wiring was on the carbon gate layer, and the wires were then connected to each other through the via holes and carbon contact layer.When a V dd was applied, the RO exhibited self-oscillation across a V dd range of 2-20 V.For example, the oscillation frequency was 28.3 Hz at V dd = 20 V as shown in Figure 4c, and therefore, the average delay time of the inverter (t d ) was estimated to be 3.5 ms.In addition, the oscillating frequency increased proportionally with increasing V dd (Figure 4d), which was attributed to the shorter delay time of the inverters with increasing V dd .This relationship between the supply voltage V dd and operating speed is known as 'voltage-dependent delay', which is a common phenomenon in CMOS circuits.This behavior suggests that the all-carbon-based circuit operates on a mechanism fundamentally similar to that of CMOS circuits.The output waveforms at each supply voltage are summarized in Figure S2 (Supporting Information).These results demonstrate that the allcarbon-based RO operated as a voltage-controlled oscillator.Notably, the RO exhibited operation even at a relatively low V dd of 2 V.

Digital Circuits: D Flip-Flop and 4 × 1 Multiplexer
Digital circuits are also extremely important in the field of electrical and computational engineering, as they serve as the foundation of digital electronic systems that are used in various applications, including computers, communication systems, control systems, and many other areas.Hence, the fabrication of all-carbon-based digital circuits is a valuable and important step toward the realization of air-stable and disposable electronic devices.
By interconnecting nine p-and nine n-type all-carbon-based OTFTs, as depicted in Figure 5a, we fabricated a positive edgetriggered DFF on a PI film as a representative digital circuit.Figure 5b shows a microscopic image of the actual circuit pattern of this film device and six electrical terminals: V dd , ground (GND), two inputs (clock and data), and two outputs (Q and NQ). Figure 5c shows the DFF operation at a clock frequency of f = 10 Hz with V dd = 10 V, demonstrating that the DFF captured the value of the data input when the clock signal transitioned from low to high (positive edge) and stably held it at the output, Q, until the next clock positive edge occurred.Synchronized with Q, NQ outputs an inverted signal.Notably, the square waves of both the clock and data inputs were generated by a signal generator, and their maximum voltages (V CLK,max and V Data,max ) were adjusted to be equal to V dd .We evaluated the maximum switching speed based on the clock frequency at which the DFF operated correctly, which resulted in a DFF response until the clock reached 200 Hz when a V dd of 10 V was applied (Figure S3c, Supporting Information).The maximum switching speed decreased as V dd decreased from 10 to 5 V (Figure S3, Supporting Information) because the delay time increased with the increasing ON-resistance of the OTFTs.Thus, a voltage-dependent delay was observed in both the all-carbon-based digital circuits and analog circuits.Furthermore, we successfully demonstrated a 2-bit Gray code counter and 3-bit shift register consisting of two and three DFFs, respectively, at a clock frequency of f = 10 Hz with V dd = V CLK,max = V Data,max = 10 V (Figure S4, Supporting Information).This indicates that all DFFs were synchronized with the clock signal, stably held their state until the next clock positive edge and showed sufficiently high and low output polarities to switch the subsequent DFF.Overall, these findings establish that the DFF characteristics could be consistently matched with good reproducibility.
Next, a 4 × 1 MUX was fabricated on the PI film from eight pand eight n-type all-carbon-based OTFTs.As shown in the circuit diagram in Figure 5d, the 4 × 1 MUX is a digital circuit composed of six transmission gates and two inverters that allows a single output line (Y) to select one of the four data lines (Data1-4) based on the values of the two selected lines (Q1 and Q2).Specifically, according to the binary values of (Q1,Q2) = (00, 01, 10, or 11), the corresponding data input is routed to output Y, as summarized in the truth table in Figure 5d.The microscopic image in Figure 5e shows the entire image of this film device, which includes 11 electrical terminals: V dd , GND, Data1-4, Q1, NQ1, Q2, NQ2, and Y.We conducted a comprehensive verification of the 4 × 1 MUX operation by connecting output signals of a 2-bit Gray code counter to two selected lines, Q1 and Q2.This counter was constructed by combining two sets of 10 Hz square waves with a phase difference of /2 rad.The output signal of the 4 × 1 Notably, all 10 V square waves of the data and selected lines were generated by signal generators, and the frequencies of Data1-4 were 1/2, 1/16th, 1/4th, and 1/8th of the Q1 frequency, respectively.

Combination of Analog and Digital Circuits
Many modern electronic systems require both analog and digital components to function properly.Therefore, it is critical to de-velop advanced and practical applications that demonstrate the integration of analog and digital circuits made of only carbonbased materials.
We assembled the abovementioned all-carbon-based circuits into a 4-bit ID output device by interconnecting them, as depicted in the circuit diagram in Figure 5g, in which the RO operated as a clock generator, the two DFFs as a 2-bit Gray code counter, and the 4 × 1 MUX as an ID-input/output terminal.All circuits shared a common GND and 10 V supply voltage as previously described.Figure 5h shows the output waveforms at each stage of the device when the 4-bit ID (Data1-4) equaled 0101.In the first stage, the RO oscillated at f = 11 Hz and output a periodic pulse-like signal.The signal was transmitted to the clock inputs of the two DFFs comprising a 2-bit Gray code counter in the second stage, and the DFFs were successfully synchronized by the RO signal that behaved as a positive edge trigger, although it was a partially distorted square waveform.This result should be emphasized because of the potential difficulty in that the clock signal must be stable and synchronize all DFFs.As a result, the two DFFs worked cooperatively to operate the counter, as shown by the output signals of Q1 and Q2 in Figure 5h, which switched sequentially and cyclically between 00 → 01 → 11 → 10 with 1/4th of the frequency of the RO signal.Notably, NQ1 and NQ2 also output inverted signals synchronized with the RO signal.In the last stage, the 4 × 1 MUX was controlled by the counter-generated Q1, NQ1, Q2, and NQ2 signals, and sequentially output the preset 4-bit ID in the order of Data1, Data3, Data4, and Data2 according to the binary values of (Q1,Q2).It is reasonable that the 4 × 1 MUX also has an output as per the 4-bit ID in other 4-bit combinations.Thus, we successfully demonstrated an all-carbon-based device that integrates analog/digital circuits.The entire device operated in air under yellow light, indicating excellent air stability.

Conclusion
In conclusion, we established a fabrication process for p-and ntype OTFTs on a PI film using exclusively carbon-based materials, such as organic compounds and inorganic carbons.These OTFTs exhibited excellent transistor characteristics, including high onoff current ratio of 10 7 , a turn-on voltage of almost 0 V, and high effective hole and electron field-effect mobilities.Leveraging these OTFTs, we fabricated analog/digital complementary integrated circuits on the PI film by interconnecting multiple pand n-type OTFTs with photolithographically patterned carbon wiring.The resulting all-carbon-based film devices, including inverters, RO, DFFs and 4 × 1 MUX, demonstrated stable operation under a supply voltage of 10 V.In addition, we successfully integrated all these circuits into a 4-bit ID output device, demonstrating the integration of analog/digital circuits using only carbonbased materials.This accomplishment marks a significant milestone in the realization of all-carbon-based film devices that operate on analog/digital complementary circuits, effectively creating a so-called metal-free device.Notably, all circuits, including the integrated device, operated in ambient air under yellow light.This development holds tremendous potential for the creation of air-stable and disposable electronics, which will find utility in the emerging IoT society.Moreover, our discovery represents a paradigm shift in the production of disposable electronic devices and presents a key step toward addressing the global environmental issues associated with e-waste.

Experimental Section
Materials: The p-type OSC, C 9 -DNBDT-NW were synthesized and purified in-house.The n-type OSC PhC 2 -BQQDI was purchased from FU-JIFILM Wako Pure Chemical Corporation, Japan.A carbon suspension, XC-9089 (Fujikura Kasei, Japan), was prepared by mixing graphite powder (average particle size: 3 μm) and carbon black with a polyacrylate binder in butyl acetate.The solid content was ≈20 wt%, in which the graphite: carbon black: binder weight ratio was 3:1:1.Ultrapure nitric acid (60%), sulfuric acid (96%), and perchloric acid (60%) for trace metal analysis were purchased from KANTO Chemical, Japan.The ICP standard solution H was purchased from KANTO Chemical, Japan.All the other chemicals and materials used were commercially available.
OSC Single-Crystalline Thin Film: As described in the previous work, [18,28] single-crystalline thin films of p-and n-type OSCs were obtained by continuous edge-casting of a 0.02 wt% solution of C 9 -DNBDT-NW in 3-chlorothiophene on a 100 mm × 100 mm UV/O 3 -treated Eagle XG glass at 90 °C and a 0.02 wt% solution of PhC 2 -BQQDI in 1-chloronaphthalene on a 100 mm × 100 mm nano-ground glass at 148 °C, [26] respectively.
Fabrication of All-Carbon-Based Complementary Integrated Circuits on Film-( 2) Gate Electrodes and Insulator: The carbon gate electrodes and wiring were fabricated using a photolithographic process as follows: A positive-tone photoresist (TLOR-P003 HP, Tokyo Ohka Kogyo, Japan) was spin-cast on the substrate and prebaked at 90 °C for 2 min.After exposure to UV light ( = 375 nm) using an MLA150-HR maskless aligner (Heidelberg Instruments, Germany) and post-baking at 110 °C for 90 s, the photoresist was developed with NMD-3 (Tokyo Ohka Kogyo, Japan) and washed with deionized water.Next, 30 nm-thick graphite-like carbon was deposited onto the surface at a rate of 0.3-0.5 Å s −1 using an EB-330 ebeam evaporator (Eiko Engineering, Japan) and tablet-shaped carbon target (Kojundo Chemical Laboratory, Japan).Ultrasonication in acetone and subsequently in IPA removed the photoresist from the substrate, resulting in patterned carbon gate electrodes and wiring.After vacuum-drying at 180 °C for 10 h, the PI/glass substrate was encapsulated by 200 nmthick parylene diX-SR (KISCO, Japan) via chemical vapor deposition, which served as a gate insulator.
Fabrication of All-Carbon-Based Complementary Integrated Circuits on Film-(3) OSCs: Both the single-crystalline thin films of p-type C 9 -DNBDT-NW and n-type PhC 2 -BQQDI were patterned and transferred onto the parylene insulator using a relay-substrate transfer technique [26] : First, the continuous edge-cast OSC films on glass substrates were cut into pieces (≈5 mm × 5 mm).Next, the substrates were placed face down on a relay substrate made of poly(dimethylsiloxane) (PDMS)/glass, and the OSC films were transferred to the relay-substrate surface by water/ethanol (7:3 v/v) and water/acetonitrile (2:8 v/v) penetration for C 9 -DNBDT-NW and PhC 2 -BQQDI, respectively. [29]Finally, the patterned p-and n-type OSC films were transferred to the appropriate sites by stamping the relay substrate onto the parylene insulator.The PI/glass substrate was baked under vacuum at 80 °C for 10 h.
Fabrication of All-Carbon-Based Complementary Integrated Circuits on Film-(4) Via Holes and Contact Electrodes: Prior to fabricating the contact electrodes, via holes were laser-drilled through the parylene insulator using a UV picosecond laser ( = 355 nm, Suzhou Delphi Laser, China) to partially connect the gate and contact layers.An XC-9089 carbon suspension was sprayed onto a PI/glass substrate surface through a CYTOP-coated stainless-steel stencil mask using an SV91 spray valve (San-Ei Tech, Japan).After removing the mask and vacuum-drying at 80 °C for 1 h, patterned carbon contact electrodes were formed, resulting in all-carbon-based film devices.The channel length (L) and width (W) were 100 μm/70 μm for the p-type OTFTs of C 9 -DNBDT-NW and 100 μm/300 μm for the n-type OTFTs of PhC 2 -BQQDI, except for those in the RO.

Fabrication of All-Carbon-Based Complementary Integrated Circuits on Film-(5) Note on Thickness of Gate Electrode and Insulator:
The gate insulator needed to be made as thin as possible to achieve a larger gate capacitance.Considering the voltage endurance of diX-SR and the previous result in OTFT manufacturing, a thickness of 200 nm was adopted to ensure the reliability of the insulator.However, steps at the edge of the gate electrode tended to cause insulation defects.To reduce the risk, the thickness of the gate electrode should be less than the thickness of the gate insulator, that is, <200 nm.The thinner the gate electrode was, the more reliable the insulation became.On the other hand, the gate electrode layer also served as the circuit's wiring, and its wiring resistance was crucial.Therefore, the thickness of the gate layer was designed to ensure that the resistance value of the wiring became ≈1/100th of those of the OSCs in their ON-state, which were 0.99 × 10 7 Ω for p-type OTFT and 1.41 × 10 7 Ω for n-type OTFT at |V G | = |V D | = 10 V, respectively (V G : gate voltage, V D : drain voltage).As a result, the thickness was determined to be 30 nm, where the resistance value of the gate layer wiring was evaluated to be 1.05 × 10 5 Ω with the layout of L/W = 15:1.
Electrical Measurement: Electrical measurements for the single transistors, inverter and RO were performed using a 4200-SCS semiconductor characterization system (Keithley, USA) in air under dark conditions.Electrical measurements for the other individual and combined circuits were performed with a DLM4038 mixed-signal oscilloscope (Yokogawa Test & Measurement Corporation, Japan) in the air under yellow light.Squarewave input signals were generated using a WF1948 multifunction generator (NF Corporation, Japan).The supply voltage for the circuits was applied using 2612A system and 2614B source meters (Keithley, USA).
Elemental Analysis: CHN elemental analysis was performed using a Vario MICRO cube (Elementar, Germany).S, F, Cl, and Br elemental analyses were performed using an ICS-1600 ion chromatography system (Thermo Scientific Dionex, USA).
Metal Content Analysis by ICP-MS-( 1) Digestion of Film Device: The film device (13.43 mg) was placed in a sealed Teflon vessel with a mixture of ultrapure HNO 3 (60%, 3.0 mL) and H 2 SO 4 (96%, 5.0 mL), heated to 180 °C by microwave using an ETHOS1 advanced microwave digestion system (Milestone, Italy) according to the program (heating time: 30 min, holding time: 10 min, maximum power: 1000 W) and then cooled to 25 °C.After adding ultrapure HClO 4 (60%, 2.0 mL) to the vessel, the mixture was heated again to 220 °C by microwave (heating time: 30 min, holding time: 20 min, maximum power: 1000 W) to form a pale-yellow transparent solution (13.66 g).No solid residue remained in the reaction mixture.
Optical Microscopy: POM images were obtained using an ECLIPSE LV100N POL polarized optical microscope (Nikon, Japan).Microscopic images of the circuits were obtained using an OPTELICS HYBRID (L) hybrid laser microscope (Lasertec, Japan).
Thickness Measurements: The thickness of the carbon electrodes and the gate insulator were measured using a Dektak XT stylus profiler (Bruker, USA).

Figure 1 .
Figure 1.Device fabrication of all-carbon-based complementary integrated circuits on a polyimide (PI) film.a) Fabrication process of the all-carbon-based complementary integrated circuit composed of p-and n-type single-crystalline organic semiconductors (OSCs) (C 9 -DNBDT-NW and PhC2 -BQQDI, respectively), carbon electrodes, carbon wiring, and a parylene diX-SR insulator on a PI film substrate.The circuit represents a complementary inverter and its four electrical terminals.First, graphite-like carbon (t = 30 nm) was patterned onto the PI film substrate to form carbon gate electrodes and wiring, and then encapsulated with parylene diX-SR (t = 200 nm) as a gate insulator.Next, the single-crystalline thin films of the OSCs were transferred onto the insulator surface, and subsequently via holes were laser-drilled through the insulator.Finally, carbon contact electrodes were formed by spraying an XC-9089 carbon suspension.b) A photo image of the e-beam deposited graphite-like carbon (t = 30 nm) on a 100 mm × 100 mm PI film substrate that was photolithographically patterned at a micrometer scale.The inset shows a microscopic image of the patterned carbon with the resolution of line/space (L/S) = 30 μm/10 μm.c) An atomic force microscopy (AFM) image of a surface of the e-beam deposited graphite-like carbon in the area of 5 μm × 5 μm.The height distribution reveals a smooth surface with a Gaussian-distributed roughness characterized by a root-mean-square (RMS) roughness of S q = 0.56 nm.d) A schematic of the spraying process to form the carbon contact electrodes on the OSCs, where an XC-9089 carbon suspension is transformed into a fine mist through the flow of atomizing gas and patterned on the PI film substrate based on the openings in the stencil mask.

Figure 2 .
Figure 2. Characteristics of the all-carbon-based organic thin-film transistors (OTFTs) and their complementary inverter on a PI film.a-f) The appearance and characteristics of the all-carbon-based OTFTs: A polarized optical microscopy (POM) image under cross-Nicol condition (a), transfer characteristics in the saturation regime (drain voltage (V D ) = −30 V) (b), and output characteristics at different gate voltages (V G ) (c) of the p-type OTFTs including C 9 -DNBDT-NW as the OSC layer; A POM image (d), transfer characteristics in the saturation regime (V D = 30 V) (e), and output characteristics at different V G (f) of the n-type OTFTs including PhC 2 -BQQDI as the OSC layer.The channel length (L) and width (W) were L/W = 100 μm/70 μm for the p-type OTFT and 100 μm/300 μm for the n-type OTFT, respectively.I D : drain current.g-i)The appearance and characteristics of the all-carbon-based complementary inverter: POM images viewed from the front and backside (g), a circuit diagram with its truth table (h), and voltage transfer curves (VTCs) along with corresponding signal gains at different supply voltages (V dd ) ranging from 5 to 30 V (i).V out : output voltage, V in : input voltage, Gain = ∂V out /∂V in .

Figure 3 .
Figure 3. Elemental composition and metal content of the all-carbon-based film device.a) Comparison between the expected values of elemental composition calculated based on the constituent materials and the measured values obtained from the elemental analysis.b) A logarithmic graph representing the content of all naturally occurring nonradioactive metallic elements measured with inductively coupled plasma mass spectrometry (ICP-MS).Only eight metals (Li, Na, Cu, Zn, Rb, Sr, Cs, and Ba) were identified and quantitatively determined.

Figure 4 .
Figure 4. Analog circuit: all-carbon-based 5-stage ring oscillator (RO) on a PI film.a,b) A circuit diagram (a) and a microscopic image (b) of the RO.The OTFTs in the loop have a tenfold longer channel length of L = 1000 μm, while the OTFTs at the output terminal have a typical channel length of L = 100 μm.The channel width is fixed at W = 70 μm for the p-type OTFTs and W = 300 μm for the n-type OTFTs, respectively.c) Output waveform of the RO at V dd = 20 V with the oscillation frequency of 28.3 Hz. d) Proportional relationship between the oscillation frequency of the RO and the corresponding V dd ranging from 2 to 20 V, indicating that the RO operates as a voltage-controlled oscillator.

Figure 5 .
Figure 5. Combination of all-carbon-based analog and digital circuits.a-c) The appearance and operating result of the all-carbon-based positive edgetriggered D flip-flop (DFF) on a PI film: A circuit diagram (a), a microscopic image of the entire film device (b), and operating waveforms of the clock/data inputs and Q/NQ outputs at V dd = 10 V (c).The maximum voltages of the clock and data signals (V CLK,max and V Data,max ) were 10 V.The clock frequency was 10 Hz.The square waves of the clock and data signals were generated by signal generators.d-f) The appearance and operating result of the allcarbon-based 4 × 1 multiplexer (MUX) on a PI film: A circuit diagram with its truth table (d), a microscopic image of the entire film device (e), and operating waveforms of an output signal (Y), four data signals (Data1-4), and two selected signals (Q1 and Q2) at V dd = 10 V (f).The maximum voltages of the data and selected signals (V Data,max and V Q,max ) were 10 V.The frequencies of Q1 and Q2 were 10 Hz, while those of Data1-4 were 1/2, 1/16th, 1/4th, and 1/8th of the Q1 frequency, respectively.The square waves of the data and selected signals were generated by signal generators.g) A circuit diagram of a 4-bit ID output device composed of the all-carbon-based analog and digital circuits, where the RO operates as a clock generator, two DFFs as 2-bit Gray code counter, and 4 × 1 MUX as an ID-input/output terminal.h) Operating waveforms of the 4-bit ID output device at V dd = 10 V with a 4-bit ID (Data1-4) = 0101, displaying outputs at each stage.