A micromachined silicon depth probe for multichannel neural recording

A process of making a new type of silicon depth-probe microelectrode array is described using a combination of plasma and wet etch. The plasma etch, which is done using a low temperature oxide (LTO) mask, enables probe thickness to be controlled over a range from 5 to 90 mu. Bending tests show that the probe's mechanical strength depends largely on shank thickness. More force can be applied to thicker shanks while thinner shanks are more flexible. One can then choose a thickness and corresponding mechanical strength using the process developed. The entire probe shaping process is performed only at low temperature, and thus is consistent with the standard CMOS fabrication. Using the probe in recording from rat's somatosensory cortex, we obtained four channel simultaneous recordings which showed clear independence among channels with a signal-to-noise ratio performance comparable with that obtained using other devices.     

A thermal signal generator probe for the study of neural thermaltransduction

The study of thermal transduction in neural tissues has been impeded by the lack of instrumentation able to generate complex, focal temperature variations. Specifically, the authors are interested in the study of neural thermal transduction within the cornea, with its homogeneous thermal conductivity and avascularity. They present a thermal signal generator probe that is capable of producing arbitrarily shaped bipolar (heating or cooling) thermal swings in a small volume of corneal tissue with which it is in contact. Heating and cooling of the probe tip are achieved by means of a Peltier effect thermoelectric device. The probe temperature, measured directly at the tip, is controlled using closed-loop control circuitry and waveform generation software on a host computer. Response characteristics of thermally sensitive C-fibers were investigated in an in vitro preparation of the rabbit cornea     

A silicon integrated strain-gage transducer with high linearity

The disadvantages of semiconductor strain-gage transducers are nonlinearity and temperature sensitivity. Using a monolithic integrated circuit Wheatstone bridge on a silicon cantilever enables linearization by variation of the location or width of the sensing devices. Excellent temperature stability is achieved by the integration itself and an additional external resistor.     

An integrated multichannel waveform generator for large-scale spatio-temporal stimulation of neural tissue

We present an ASIC designed for electrical stimulation of neural tissue using multielectrode arrays. The ASIC is foreseen for applications in systems that require simultaneous stimulation and recording of signals from various types of neural tissue, both in vitro and in vivo. The developed ASIC comprises 64 independent stimulation channels, which are capable to generate arbitrarily defined bipolar current or voltage waveforms, controlled in real time with time resolution of 12.5 μs and amplitude resolution of 7 bits. The amplitude range of output signal can be scaled over a very wide range, which ensures compatibility with various electrode arrays of different size and geometry. Each channel is also equipped with a stimulation artifact suppressor controlled in real time, which reduces the dead time of the system after each stimulation pulse.     

A thermal monitoring sheet with low influence from adjacent waterbolus for tissue surface thermometry during clinical hyperthermia

This paper presents a complete thermal analysis of a novel conformal surface thermometer design with directional sensitivity for real-time temperature monitoring during hyperthermia treatments of large superficial cancer. The thermal monitoring sheet (TMS) discussed in this paper consists of a 2-D array of fiberoptic sensors embedded between two layers of flexible, low-loss, and thermally conductive printed circuit board (PCB) film. Heat transfer across all interfaces from the tissue surface through multiple layers of insulating dielectrics surrounding the small buried temperature sensor and into an adjacent temperature-regulated water coupling bolus was studied using 3-D thermal simulation software. Theoretical analyses were carried out to identify the most effective differential TMS probe configuration possible with commercially available flexible PCB materials and to compare their thermal responses with omnidirectional probes commonly used in clinical hyperthermia. A TMS sensor design that employs 0.0508-mm Kapton MTB and 0.2032-mm Kapton HN flexible polyimide films is proposed for tissue surface thermometry with low influence from the adjacent waterbolus. Comparison of the thermal simulations with clinical probes indicates the new differential TMS probe design to outperform in terms of both transient response and steady-state accuracy in selectively reading the tissue surface temperature, while decreasing the overall thermal barrier of the probe between the coupling waterbolus and tissue surface.      

A 2.4-GHz silicon bipolar oscillator with integrated resonator

A 2.4 GHz fully-monolithic silicon-bipolar oscillator circuit implemented in a 12 GHz BiCMOS technology is presented. The integrated resonator circuit uses three different versions of a 2 nH multilevel inductor and a wideband capacitive transformer. The measured Q factor is 9.3 for the three-level inductor. An oscillator phase noise of -78 dBc/Hz is achieved at 20 kHz offset. The circuit dissipates 50 mW from a 3.6 V supply     

A high-yield fabrication process for silicon neural probes

There is a great need for silicon microelectrodes that can simultaneously monitor the activity of many neurons in the brain. However, one of the existing processes for fabricating silicon microelectrodes-reactive-ion etching in combination with anisotropic KOH etching-breaks down at the wet-etching step for device release. Here we describe a modified wet-etching sidewall-protection technique for the high-yield fabrication of well-defined silicon probe structures, using a Teflon shield and low-pressure chemical vapor deposition (LPCVD) silicon nitride. In the proposed method, a micro-tab holds each individual probe to the central scaffold, allowing uniform anisotropic KOH etching. Using this approach, we obtained a well-defined probe structure without device loss during the wet-etching process. This simple method yielded more accurate fabrication and an improved mechanical profile.     

A silicon integrated circuit force sensor

A piezoresistive bridge and integrated circuit amplifier can be made in the same silicon cantilever. The purpose of the amplifier is to linearize as well as amplify the output.     

A lumped scalable model for silicon integrated spiral inductors

A lumped scalable model for spiral inductors in silicon bipolar technology has been developed. The effect of three different cross sections on inductor performance was first investigated by comparing experimental measurements. Using both the results of this analysis and three-dimensional electromagnetic simulation guidelines, several circular inductors were integrated on a radial patterned ground shield for model validation purposes. The model employs a novel equation for series resistance with only one fitting parameter extracted from experimental measurements. All other model elements were related to technological and geometrical data by using rigorous analytical equations. The model was validated using one- and two-port measured performance parameters of 45 integrated inductors, and excellent agreement was found for all considered geometries up to frequencies well above self-resonance.     

Optical detection of charge modulation in silicon integrated circuits using a multimode laser-diode probe

This paper reports on the detection of sheet charge densities in silicon devices using an improved noninvasive optical probe based on the detection of free-carrier optical dispersion using a multilongitudinal-mode 1.3-µm semiconductor laser. The improved system incorporates a differential detection technique and a Wollaston prism that allows the use of the multimode laser. These changes increase stability, sensitivity, and bandwidth, allow near shot-noise limited operation, reduce required optical power, and simplify the apparatus. The technique can be applied to probe electronic signals or, conversely, to modulate light using controlled electronic signals. Simple demonstrations of each application are presented.     

A silicon micromachined scanning thermal profiler with integratedelements for sensing and actuation

The thermal profiler is a scanning probe microscope with a miniature thermocouple (TC) at its tip which provides topographic and thermographic information by sensing heat conducted across a small air gap. The silicon micromachined thermal profilers (SMTPs) described in this paper are structurally comprised of a probe that can be longitudinally actuated by an integrated electrostatically driven suspension. A polysilicon-gold TC is located near the probe tip, which overhangs a glass substrate; a resistive heater is integrated with the base. An IC-compatible, 8-mask fabrication process has been developed and SMTPs with various types of frames and probes have been designed, fabricated, and thermally characterized. The maximum thermoelectric signal available from a 7-TC thermopile probe has been measured at 824 mV/W of input power to the heater, whereas from a simpler design it was 48 mV/W. Simple dithered and nondithered scans are presented to demonstrate the basic functionality of fabricated devices. The noise due to our test setup has been measured at ≈20 mK. For a 1 μm×0.5 μm tip and a 0.1 μm long air gap the spatial resolution and the device NETD have been theoretically estimated as ≈3.33 nm and ≈0.1 mK/√Hz, respectively     

A hybrid neural network model for predicting silicon content

The silicon content of the hot metal in the blast furnace ironmaking process normally reflects the thermal state of the furnace and affects the fuel rate. In this paper a hybrid neural network model is proposed to predict the silicon contentn steps ahead. A time-delay neural network, which has self-loops to represent dynamics, is adopted here. The learning procedure of this network has been divided into two states. A BP algorithm with forgetting factor is first introduced to find the appropriate structure of the network. The temporal difference (TD) method with forgetting factor is then used forn-step-ahead prediction. The results show that the method can perform satisfactoryn-step-ahead prediction and is suited for implementation.     

Metallization systems for silicon integrated circuits

An investigation into single and composite layered metallization systems is described with respect to their limitations, possible failure mechanisms, and problems encountered in fabrication. Systems investigated include metals such as chromium, titanium, tungsten, and molybdenum in conjunction with gold. Comparisons are made to conventional aluminum with respect to ohmic contact to silicon, metallurgical reactions, behavior in adverse environmental conditions, method of deposition, and processing difficulties.     

Polycrystalline silicon resistors for integrated circuits

The suitability of thin films of doped polycrystalline silicon on SiO₂ substrates for the production of high value resistors for monolithic integrated circuits is considered. Resistors fabricated from this material posses the advantages of high sheet resistivity and dielectric isolation while still preserving an all silicon technology compatible with conventional production techniques.Relevant structural and electrical properties of doped polycrystalline films produced by both vacuum evaporation onto hot substrates with gas-doping and by diffusion-annealing of amorphous films have been investigated. Sheet resistivities and TCR values measured on 2500 Å polycrystalline films have proved superior to those encountered with conventional diffused resistors. Typically films with sheet resistivities of 1 kΩ/□ had TCR's of ?1000 ppm/°C while conventional diffused resistors are generally made from material of 200 Ω/□ and +2000 ppm/°C TCR. Etched resistor line widths of 0·25 mil. have been obtained in the polycrystalline material employing conventional photolithographic techniques. The temperature stability and linearity of doped polycrystalline resistors have been investigated.     

A sample-and-hold current measurement integrated circuit for neural recording

This paper describes a new differential sample-and-hold technique of current measurement for neural probing. The design utilizes bottom plate sampling (BPS) and T-transmission switches to mitigate signal coupling and a differential sample-and-hold technique to reduce charge injection and clock feed through. The circuit was fabricated in a 0.35?µm CMOS process and tested using different input loads to model the electrochemical properties of the microelectrode. Test results matched closely with the simulation results, proving that the concept of the sample-and-hold current measurement circuit is valid for neural probing.     

A new model for the thermal oxidation kinetics of silicon

A model is presented which reasons that the thermal oxidation of silicon is surface reaction limited, and that the reaction rate is controlled by the viscous flow of newly forming oxide to accommodate the volume expansion that occurs when silicon oxidizes. The SiO₂ must form at silicon lattice sites and therefore epitaxially. This thermody-namically unstable epitaxial structure reconfigures and this reconfiguration results in an increase of the average viscosity of the oxide. The continual increase of average oxide viscosity accounts for the continual decrease in oxidation rate with time. A mathemat-ical analysis based on this model is used to derive the simple power law x = at^b relating oxide thickness, x, to oxidation time, t which has been shown previously to model phe-nomenologically all of the extant dry oxidation data.¹ The physical significances of the coefficient a and exponent b are obtained by the interpretation of the x vs t data in the literature in terms of this mathematical analysis.     

GaAs MQW modulators integrated with silicon CMOS

We demonstrate integration of GaAs-AlGaAs multiple quantum well modulators to silicon CMOS circuitry via flip-chip solder-bonding followed by substrate removal. We obtain 95% device yield for 32×32 arrays of devices with 15 micron solder pads. We show operation of a simple circuit composed of a modulator and a CMOS transistor     

Embedded benzocyclobutene in silicon: An integrated fabrication process for electrical and thermal isolation in MEMS

This paper reports a novel fabrication process to develop planarized isolated islands of benzocyclobutene (BCB) polymer embedded in a silicon substrate. Embedded BCB in silicon (EBiS) can be used as an alternative to silicon dioxide in fabrication of electrostatic micromotors, microgenerators, and other microelectromechanical devices. EBiS takes advantage of the low dielectric constant and thermal conductivity of BCB polymers to develop electrical and thermal isolation integrated in silicon. The process involves conventional microfabrication techniques such as photolithography, deep reactive ion etching, and chemical mechanical planarization (CMP). We have characterized CMP of BCB polymers in detail since CMP is a key step in EBiS process. Atomic force microscopy (AFM) and elipsometry of blanket BCB films before and after CMP show that higher polishing down force pressure and speed lead to higher removal rate at the expense of higher surface roughness, non-uniformity, and scratch density. This is expected since BCB is a softer material compared to inorganic films such as silicon dioxide. We have observed that as the cure temperature of BCB increases beyond 200 °C, the CMP removal rate decreases drastically. The results from optical microscopy, scanning electron microscopy, and optical profilometry show excellent planarized surfaces on the EBiS islands. An average step height reduction of more than 95% was achieved after two BCB deposition and three CMP steps.     

A fully integrated neural recording amplifier with DC input stabilization

This paper presents a low-power low-noise fully integrated bandpass operational amplifier for a variety of biomedical neural recording applications. A standard two-stage CMOS amplifier in a closed-loop resistive feedback configuration provides a stable ac gain of 39.3 dB at 1 kHz. A subthreshold PMOS input transistor is utilized to clamp the large and random dc open circuit potentials that normally exist at the electrode-electrolyte interface. The low cutoff frequency of the amplifier is programmable up to 50 Hz, while its high cutoff frequency is measured to be 9.1 kHz. The tolerable dc input range is measured to be at least +/- 0.25 V with a dc rejection factor of at least 29 dB. The amplifier occupies 0.107 mm2 in die area, and dissipates 115 microW from a 3 V power supply. The total measured input-referred noise voltage in the frequency range of 0.1-10 kHz is 7.8 microVrms. It is fabricated using AMI 1.5 microm double-poly double-metal n-well CMOS process. This paper presents full characterization of the dc, ac, and noise performance of this amplifier through in vitro measurements in saline using two different neural recording electrodes.     

用于齿轮检测的集成式测量头电路设计

为了降低测量头噪音,提高测量精度,增强其使用灵活性,进行了扫描式电感测量头的集成化研究.采用了传感器与信号处理电路均集成在测量头中,并使其具备显示功能与标准串行通讯接口的设计方案,讨论了相关电路的.设计与开发.信号调理电路使用了差动电感信号调理单芯片解决方案AD698,而后续处理电路则基于内部集成有高速、高精度MD转换器以及其他功能模块的SOC型单片机C805 1F060进行构建.对所开发电路进行了测试和实验,实验结果达到了预期要求.