Measurement of Electrophysiological Signals In Vitro Using High-Performance Organic Electrochemical Transistors

Biological environments use ions in charge transport for information transmission. The properties of mixed electronic and ionic conductivity in organic materials make them ideal candidates to transduce physiological information into electronically processable signals. A device proven to be highly successful in measuring such information is the organic electrochemical transistor (OECT). Previous electrophysiological measurements performed using OECTs show superior signal-to-noise ratios than electrodes at low frequencies. Subsequent development has significantly improved critical performance parameters such as transconductance and response time. Here, interdigitated-electrode OECTs are fabricated on flexible substrates, with one such state-of-the-art device achieving a peak transconductance of 139 mS with a 138 µs response time. The devices are implemented into an array with interconnects suitable for micro-electrocorticographic application and eight architecture variations are compared. The two best-performing arrays are subject to the full electrophysiological spectrum using prerecorded signals. With frequency filtering, kHz-scale frequencies with 10 µV-scale voltages are resolved. This is supported by a novel quantification of the noise, which compares the gate voltage input and drain current output. These results demonstrate that high-performance OECTs can resolve the full electrophysiological spectrum and suggest that superior signal-to-noise ratios could be achieved in high frequency measurements of multiunit activity.     

Tuning Channel Architecture of Interdigitated Organic Electrochemical Transistors for Recording the Action Potentials of Electrogenic Cells

Organic electrochemical transistors (OECTs) have emerged as versatile electrophysiological sensors due to their high transconductance, biocompatibility, and transparent channel material. High maximum transconductances are demonstrated facilitating the extracellular recording of signals from electrogenic cells. However, this requires large channel dimensions and thick polymer films. These large channel dimensions lead to low transistor densities. Here, interdigitated OECTs (iOECTs) are introduced, which feature high transconductances at small device areas. A superior device performance is achieved by systematically optimizing the electrode layout regarding channel length, number of electrode fingers and electrode width. Interestingly, the maximum transconductance (g_max) does not straightforwardly scale with the channel width‐to‐length ratio, which is different from planar OECTs. This deviation is caused by the dominating influence of the source–drain series resistance R_sd for short channel devices. Of note, there is a critical channel length (15 µm) above which the channel resistance R_ch becomes dominant and the device characteristics converge toward those of planar OECTs. Design rules for engineering the performance of iOECTs are proposed and tested by recording action potentials of cardiomyocyte‐like HL‐1 cells with high signal‐to‐noise ratios. These results demonstrate that interdigitated OECTs meet two requirements of bioelectronic applications, namely, high device performance and small channel dimensions.     

High-Gain Chemically Gated Organic Electrochemical Transistor

Organic electrochemical transistors (OECTs) have exhibited promising performance as transducers and amplifiers of low potentials due to their exceptional transconductance, enabled by the volumetric charging of organic mixed ionic/electronic conductors (OMIECs) employed as the channel material. OECT performance in aqueous electrolytes as well as the OMIECs’ redox activity has spurred a myriad of studies employing OECTs as chemical transducers. However, the OECT's large (potentiometrically derived) transconductance is not fully leveraged in common approaches that directly conduct chemical reactions amperometrically within the OECT electrolyte with direct charge transfer between the analyte and the OMIEC, which results in sub-unity transduction of gate to drain current. Hence, amperometric OECTs do not truly display current gains in the traditional sense, falling short of the expected transistor performance. This study demonstrates an alternative device architecture that separates chemical transduction and amplification processes on two different electrochemical cells. This approach fully utilizes the OECT's large transconductance to achieve current gains of 10³ and current modulations of four orders of magnitude. This transduction mechanism represents a general approach enabling high-gain chemical OECT transducers.     

RF PDSOI LDMOS器件的电离总剂量辐照效应

研制了一种用于射频领域的叉指栅PDSOI LDMOS晶体管,并分析了总剂量辐照对其静态和小信号射频特性的影响. 其静态工作模式下的辐照响应由前/背栅阈值、泄漏电流、跨导和输出特性表征,而其交流工作模式下的辐照响应由截止频率和最高振荡频率表征. 实验表明,在室温环境下经过总剂量为1Mrad(Si)的γ射线辐照,不同尺寸和结构的射频SOI LDMOS晶体管的各项指标均表现出明显退化,并且仅当器件工作在静态模式时LBBC LDMOS才表现出优于BTS LDMOS的抗辐照性能.     

RF PDSOI LDMOS器件的电离总剂量辐照效应

研制了一种用于射频领域的叉指栅PDSOI LDMOS晶体管,并分析了总剂量辐照对其静态和小信号射频特性的影响.其静态工作模式下的辐照响应由前/背栅阈值、泄漏电流、跨导和输出特性表征,而其交流工作模式下的辐照响应由截止频率和最高振荡频率表征.实验表明,在室温环境下经过总剂量为1Mrad(Si)的γ射线辐照,不同尺寸和结构的射频SOI LDMOS晶体管的各项指标均表现出明显退化,并且仅当器件工作在静态模式时LBBC LDMOS才表现出优于BTS LDMOS的抗辐照性能.     

Balancing Ionic and Electronic Conduction for High‐Performance Organic Electrochemical Transistors

Conjugated polymers that support mixed (electronic and ionic) conduction are in demand for applications spanning from bioelectronics to energy harvesting and storage. To design polymer mixed conductors for high‐performance electrochemical devices, relationships between the chemical structure, charge transport, and morphology must be established. A polymer series bearing the same p‐type conjugated backbone with increasing percentage of hydrophilic, ethylene glycol side chains is synthesized, and their performance in aqueous electrolyte gated organic electrochemical transistors (OECTs) is studied. By using device physics principles and electrochemical analyses, a direct relationship is found between the OECT performance and the balanced mixed conduction. While hydrophilic side chains are required to facilitate ion transport—thus enabling OECT operation—swelling of the polymer is not de facto beneficial for balancing mixed conduction. It is shown that heterogeneous water uptake disrupts the electronic conductivity of the film, leading to OECTs with lower transconductance and slower response times. The combination of in situ electrochemical and structural techniques shown here contributes to the establishment of the structure–property relations necessary to improve the performance of polymer mixed conductors and subsequently of OECTs.     

Mechanism of negative transconductance in heterostructurefield-effect transistors

In most heterostructure field-effect transistors the drain current at very large gate voltages drops with an increase of the gate voltage leading to a negative device transconductance. Based on the analysis of the gate and channel current distributions in such devices, it is shown that the negative transconductance at large gate currents is related to the dramatic change in the electric field distribution in the channel and to the saturation of the density of the two-dimensional electron gas in the channel. Under such conditions the electric field increases at the source side of the channel where the gate current primarily flows. When the electric field at the source side exceeds the electric field at the drain side of the channel, the device transconductance becomes negative. This is related to a higher voltage drop near the source side of the channel causing a partial depletion in the channel     

A novel CMOS triode transconductor based on current division

A compact transconductor based on transistors operating in the triode region is presented. A novel V–I conversion stage made up of current dividers is proposed. The circuit allows tunability by adjusting a dc current and the transconductance is independent of transconductance parameter of the triode transistors. Besides, the circuit is simple because feedback structures to fix source-drain voltages of triode transistors are not needed, saving area and featuring low power consumption. Measurement and simulation results are presented and analyzed for validating the proposed technique.     

Influence of gate-to-source and gate-to-drain recesses on GaAs camel-like gate field-effect transistors

In this article, the characteristics of the GaAs homojunction camel-like gate field-effect transistors with and without the gate-to-source and gate-to-drain recesses structures are first investigated and compared. As to the device without the recesses structure, a second channel within the n ⁺-GaAs cap layer is formed at large gate bias, which could enhance the drain output current and transconductance. Furthermore, a two-stage relationship between drain current (and transconductance) versus gate voltage is observed in the recesses structure. The simulated results exhibit a maximum drain saturation current of 447 (351 mA/mm) and a maximum transconductance of 525 (148 mS/mm) in the studied device without (with) the recesses structure. Consequentially, the demonstration and comparison of the variable structures provide a promise for design in circuit applications.     

High-Speed Operation of Electrochemical Logic Circuits Depending on 3D Construction of Transistor Architectures

The emergence of organic electrochemical transistors (OECTs) has opened a new era of printable electronics and bioelectronics, due to their unique advantages including innately superior transconductance and biocompatibility. Despite the foreseeable advancements available from their further implementations in fundamental logic circuitry, however, insufficient operation speeds and short compatibilities to scaling-down have so far hindered advanced integrations other than biosensing and biosignal amplifications. Here, a 3D-construction-dependent operational analysis of OECTs is reported, with which an all-vertical architectural design enabled unprecedentedly high operating speed and a facile expansion to large-area and high-density 3D crossbar arrays. A simple vertical channel architecture completed with solid-state Ag/AgCl top-gate electrodes enables an ultrafast redistribution of ions within channels, yielding a state-of-the-art operation frequency reaching 12 MHz V⁻¹. Various printed logic circuit arrays, including NOT, NAND, and NOR gates, with high stability and reproducibility.     

Quantum-well p-channel AlGaAs/InGaAs/GaAs heterostructureinsulated-gate field-effect transistors with very high transconductance

Quantum-well p-channel pseudomorphic AlGaAs/InGaAs/GaAs heterostructure insulated-gate field-effect transistors with enhanced hole mobility are described. The devices exhibit room-temperature transconductance, transconductance parameter, and maximum drain current as high as 113 mS/mm, 305 mS/V/mm, and 94 mA/mm, respectively, in 0.8-μm-gate devices. Transconductance, transconductance parameter, and maximum drain current as high as 175 mS/mm, 800 mS/V/mm, and 180 mA/mm, respectively were obtained in 1-μm p-channel devices at 77 K. From the device data hole field-effect mobilities of 860 cm²/V-s at 300 K and 2815 cm²/V-s at 77 K have been deduced. The gate current causes the transconductance to drop (and even to change sign) at large voltage swings. Further improvement of the device characteristics may be obtained by minimizing the gate current. To this end, a type of device structure called the dipole heterostructure insulated-gate field-effect transistor is proposed     

Single-Material OECT-Based Flexible Complementary Circuits Featuring Polyaniline in Both Conducting Channels

The organic electrochemical transistor (OECT) with a conjugated polymer as the active material is the elementary unit of organic bioelectronic devices. Improved functionalities, such as low power consumption, can be achieved by building complementary circuits featuring two or more OECTs. Complementary circuits commonly combine both p- and n-type transistors to reduce power draw. While p-type OECTs are readily available, n-type OECTs are less common mainly due to poor stability of the n-type active channel material in aqueous electrolyte. Here, a complementary circuit is made using a pair of OECTs having polyaniline (PANI) as the channel material in both transistors. PANI, with a finite electrochemical window accessible at voltages lower than 1 V, exhibits a peak in current versus gate voltage when used as an active channel in an OECT. The current peak has two slopes, one n-like and one p-like, which correspond to different electrochemical regimes of the same underlying conjugated polymer. The electrochemistry enables the design of a complementary circuit using only PANI as the channel material. The PANI-based circuit is shown to have excellent performance with gain of ≈7 and is transferred on a flexible biocompatible chitosan substrate with demonstrated operation in aqueous electrolyte.     

Worst case estimate of mismatch induced distortion in complementaryCMOS current mirrors

Mismatching between the MOS transistors in a current mirror causes harmonic distortion. In a complementary class AB current mirror, mismatching of threshold voltages, geometries and transconductance parameters causes a distortion which cannot be eliminated by circuit techniques but which can be reduced by careful device matching. In this Letter, the author presents a worst case estimate of the harmonic distortion introduced by device mismatch     

Enhancement-mode metal/(Al,Ga)As/GaAs buried-interface field-effect transistor (BIFET)

Undoped Al0.5Ga0.5As is used as an insulator layer in the fabrication of MIS-type buried-interface field-effect transistors (BIFETs). The devices had a 2.5 ?m-long gate and an insulator layer 1000 ? thick. When operated in an accumulation mode the transconductance and maximum current increased from 21 mS/mm and 77 mA/mm at 300 K to 40 mS/mm and 138 mA/mm at 77 K, respectively. The maximum possible 77 K transconductance is calculated as approximately 130 mS/mm. These preliminary experimental results are the best yet reported for a GaAs MIS-type device and represent the first report of enhanced device performance at cryogenic temperatures as a result of an increased electron saturation velocity.     

Simplified Large‐Area Manufacturing of Organic Electrochemical Transistors Combining Printing and a Self‐Aligning Laser Ablation Step

A hybrid manufacturing approach for organic electrochemical transistors (OECTs) on flexible substrates is reported. The technology is based on conventional and digital printing (screen and inkjet printing), laser processing, and post‐press technologies. A careful selection of the conductive, dielectric, and semiconductor materials with respect to their optical properties enables a self‐aligning pattern formation which results in a significant reduction of the usual registration problems during manufacturing. For the prototype OECTs, based on this technology, on/off ratios up to 600 and switching times of 100 milliseconds at gate voltages in the range of 1 V were obtained.     

Modeling of a Room-Temperature Silicon Quantum Dot-Based Single-Electron Transistor and the Effect of Energy-Level Broadening on Its Performance

In this work, we have modeled silicon quantum dot (QD)-based single-electron transistors (SETs) operating at room temperature and investigated the effect of the QD’s energy-level broadening on the performance of the SET. First we obtained the energy levels and corresponding wave functions for spherical Si QDs by solving the coupled Schrödinger–Poisson equations in three dimensions. Then, we demonstrated different tunneling current rates for separated energy levels by considering nonequal energy-level broadenings. Accordingly, an expression for the corresponding tunneling rates in the quantum Coulomb blockade regime was derived. In the next step, the transconductance characteristics of the Si QD SET device with Coulomb oscillations were simulated, and their differences from previously investigated metal-based SETs were demonstrated. Finally, by applying different bias voltages, we determined the effect of temperature variations on the transconductance characteristics.     

p-Type SiGe transistors with low gate leakage using SiN gatedielectric

Using high-quality jet-vapor-deposited (JVD) SiN as gate dielectric, p-type SiGe transistors are fabricated on SiGe heterostructures grown by ultra-high-vacuum chemical vapor deposition (UHVCVD). For an 0.25-μm gate-length device, the gate leakage current is as small as 2.4 nA/mm at V_ds=-1.0 V and V_gn=0.4 V. A maximum extrinsic transconductance of 167 mS/mm is measured. A unity current gain cutoff frequency of 27 GHz and a maximum oscillation frequency of 35 GHz are obtained     

Computer analysis of the double-diffused MOS transistor for integrated circuits

The effective length of an MOS transistor can be made narrow by using double diffusion similar to a bipolar transistor. Computations were conducted for an n-channel double-diffused transistor with different surface concentrations, channel lengths, channel gradients, surface-states densities, and substrate concentrations. A shorter channel length and a higher surface-state density, e.g.langle1, 1, 1ranglecrystal, gave a higher drain current and transconductance. The maximum transconductance in many cases occurs at low gate voltages. The computations indicate that a gain-bandwidth product in the gigahertz range can be expected when the graded channel region is less than 1 µm. The difference between an n-type substrate and a p-type substrate is not substantial. The analysis is also useful in predicting the performance of any integrated logic circuit using the diffused enhancement transistor as the active switch and a depletion-mode transistor (without a diffused channel) as the load device. The computation indicates that satisfactory performance can be obtained using a load device with the same geometry and an ON voltage of only a fraction of a volt, This revelation indicates that double-diffused channel MOS transistors not only give higher speed but also smaller chip area for integrated circuits and a lower supply voltage (hence less power dissipation).     

The fabrication and characterization of poly(4-vinylpyridine)-based thin film transistors exhibiting enhanced ion modulation

Lithium perchlorate-doped hygroscopic poly(4-vinylpyridine)-based organic thin film transistors have been fabricated and characterized. More than one mechanism of current modulation is observed in these devices with the observed mechanism depending upon both the amount of added dopant and the operating voltage. At low gate voltages (0 to −0.8 V) the current modulation mechanism is dominated by ions intrinsic to the dielectric layer (due to its hygroscopic nature), while at higher gate voltages (−1 to −2 V) the device behavior is governed by the movement of the dopant ions. Most importantly, through careful control of dopant concentration, we show that it is now possible to fabricate all-solution processed devices with significantly enhanced current modulation. In particular, we demonstrate that current modulation ratios in excess of 10⁵ are possible with this device architecture.     

n-Type Glycolated Imide-Fused Polycyclic Aromatic Hydrocarbons with High Capacity for Liquid/Solid-Electrolyte-based Electrochemical Devices

Currently, n-type small-molecule mixed ionic-electronic conductors remain less explored and their molecular design rules are not mature enough. Herein, two n-type glycolated imide-fused polycyclic aromatic hydrocarbons (IPAHs), d-gdiPDI and t-gdiPDI, are developed to probe the effects of molecular conformation on the electronic, electrochemical, morphological, and coupled ionic-electronic transport properties. It is found that the highly twisted scaffold in d-gdiPDI, compared to the nearly planar one of t-gdiPDI, has a strong positive effect on the charge storage properties and thus the performance of organic electrochemical transistors (OECTs). d-gdiPDI exhibits a volumetric capacitance of 657 F cm⁻³, obviously outperforming that of t-gdiPDI (261 F cm⁻³), which is the highest value reported to date for small-molecule OECT materials. Moreover, a high charge-storage capacity of up to 479 F g⁻¹ is observed for d-gdiPDI. Arising from such high ionic-electronic coupling characteristic, d-gdiPDI-based OECTs present a ≈2 × times higher geometry-normalized transconductance (g_m,norm) of 105.3 mS cm⁻¹ relative to that of t-gdiPDI counterparts. Significantly, further application of d-gdiPDI in solid-electrolyte OECTs delivers a g_m,norm of 142.4 mS cm⁻¹. These findings indicate that IPAHs are very promising candidates for n-type small-molecule OECTs and highlight the superiority of twisting conformation manipulation in materials design toward high-performance electrochemical devices.