Silicon Microprobes Research Articles

In-Line Measurement of the Surface Texture of Rolls Using Long Slender Piezoresistive Microprobes.

Long slender piezoresistive silicon microprobes are a new type of sensor for measurement of surface roughness. Their advantage is the ability to measure at speeds of up to 15 mm/s, which is much faster than conventional stylus probes. The drawbacks are their small measurement range and tendency to break easily when deflected by more than the allowed range of 1 mm. In this article, previously developed microprobes were tested in the laboratory to evaluate their metrological properties, then tested under industrial conditions. There are several industrial measurement applications in which microprobes are useful. Measurement of the roughness of paper machine rolls was selected for testing in this study. The integration of a microprobe into an existing roll measurement device is presented together with the measurement results. The results are promising, indicating that measurements using a microprobe can give useful data on the grinding process.

ПРОЕКТИРОВАНИЕ КРЕМНИЕВОГО МИКРОЗОНДА ДЛЯ МАЛОИНВАЗИВНОГО НЕЙРОИНТЕРФЕЙСА

Microprobes have become an important tool in the study of brain activity. Research and developmentin the field of invasive neurointerfaces is aimed at reducing the characteristic damageto the nervous tissue by reducing the diameter of the implanted probes to less than 100 μm. Suchstructures are produced by micromachining, in particular, by types of anisotropic etching. In thiscase, the size and shape of the probe are influenced by the etching conditions. The latter should betaken into account at the designing of the probe. The paper evaluates the ranges of the geometricparameters of a silicon microprobe taking into account the etching conditions and the number ofelectrodes. Analytical calculations were carried out for the structure of the probe, represented byfour regions of different widths, carrying up to seven electrodes. The dependences of bottom basewidth of a trapezoidal section of the probe and the size of the mask on the thickness and width ofthe top base are received. The admissible ranges of sizes for the proposed case of the four-levelmicroprobe are established; in particular, the minimum values of the width of the top base were17, 28, 39 and 50 microns, and the corresponding ranges of permissible values of the probe thicknessfor cases with 1 electrode – 30–58 microns, 2 and 3 electrodes – 30–51 microns, 4 and 5electrodes – 30–43 microns, and for the case of a probe with 6 and 7 electrodes – 30–35 microns.The correction value of the mask size is estimated, reflecting the effect of etching conditions on theprobe geometry.

Customized piezoresistive microprobes for combined imaging of topography and mechanical properties

Customized piezoresistive cantilever microprobes with a deflection range of 120 ​μm and silicon tips of 100 ​μm height were operated in a Cypher AFM showing their functionality for measuring topography together with viscoelastic properties of thin films. For drop-in mounting in the AFM a holder was developed comprising the piezoresistive microprobe and its voltage-supply and signal-conditioning electronics. With the probe tip in contact to a glass sample we found a vertical resolution of 2.8 ​nm in a bandwidth of 1 ​kHz, which is close to the theoretical limit of 3.0 ​nm ​at a deflection of 2.5 ​μm. This resolution could be verified in topographic images of a scratch of approximately 300 ​nm in depth. Force-volume images with lithographically patterned photoresist (AZ 5214E) of approximately 300 ​nm thickness on silicon revealed contrast of the resist-covered and bare regions in topography, stiffness and adhesion. With contact-resonance imaging using the Dual AC Resonance Tracking (DART) method, patterned AZ 5214E photoresist of approximately 50 ​nm thickness could be distinguished from the bare silicon in topography, contact stiffness (indicated by contact resonance frequency shift) and adhesion (indicated by phase shift). Finally, a droplet of lubricant (Lupranol VP 9209) on glass could be detected by force volume imaging revealing a thickness of approximately 90 ​nm of the liquid layer with a sharp lateral limitation, which was clearly detected. We conclude that the piezoresistive silicon microprobe is a promising tool for emerging tasks of industrial surface metrology on manufacturing machines, including micro-finish of work pieces and elasticity, thickness, adhesion, etc. of thin solid or liquid deposits on top.

Investigating the Trackability of Silicon Microprobes in High-Speed Surface Measurements

High-speed tactile roughness measurements set high demand on the trackability of the stylus probe. Because of the features of low mass, low probing force, and high signal linearity, the piezoresistive silicon microprobe is a hopeful candidate for high-speed roughness measurements. This paper investigates the trackability of these microprobes through building a theoretical dynamic model, measuring their resonant response, and performing tip-flight experiments on surfaces with sharp variations. Two microprobes are investigated and compared: one with an integrated silicon tip and one with a diamond tip glued to the end of the cantilever. The result indicates that the microprobe with the silicon tip has high trackability for measurements up to traverse speeds of 10 mm/s, while the resonant response of the microprobe with diamond tip needs to be improved for the application in high-speed topography measurements.

Open source silicon microprobes for high throughput neural recording

Objective. Microfabricated multielectrode arrays are widely used for high throughput recording of extracellular neural activity, which is transforming our understanding of brain function in health and disease. Currently there is a plethora of electrode-based tools being developed at higher education and research institutions. However, taking such tools from the initial research and development phase to widespread adoption by the neuroscience community is often hindered by several obstacles. The objective of this work is to describe the development, application, and open dissemination of silicon microprobes for recording neural activity in vivo. Approach. We propose an open source dissemination platform as an alternative to commercialization. This framework promotes recording tools that are openly and inexpensively available to the community. The silicon microprobes are designed in house, but the fabrication and assembly processes are carried out by third party companies. This enables mass production, a key requirement for large-scale dissemination. Main results. We demonstrate the operation of silicon microprobes containing up to 256 electrodes in conjunction with optical fibers for optogenetic manipulations or fiber photometry. These data provide new insights about the relationship between calcium activity and neural spiking activity. We also describe the current state of dissemination of these tools. A file repository of resources related to designing, using, and sharing these tools is maintained online. Significance. This paper is likely to be a valuable resource for both current and prospective users, as well as developers of silicon microprobes. Based on their extensive usage by a number of labs including ours, these tools present a promising alternative to other types of electrode-based technologies aimed at high throughput recording in head-fixed animals. This work also demonstrates the importance of validating fiber photometry measurements with simultaneous electrophysiological recordings.

Microprobe electrode array with individual interconnects through substrate using silicon through-glass via

This paper presents the fabrication and measurements of a vertical out-of-plane microprobe electrode array with individual interconnects through the substrate using a silicon through-glass via (TGV) with transparent properties. The TGV was fabricated using a low-resistance silicon (LRS) via and the glass reflow process. The microprobe structure was formed by multiple deep reactive ion etching and reactive ion etching processes using one-step photolithography and a single etch mask. The height and pitch of the microprobe are designed to be 90 μm and 210 μm, respectively. Cr and Au conductive layers were deposited and patterned on the silicon microprobe structure. A parylene-C thin film was used as an insulating layer and it was etched only at the tip-end through the self-alignment fabrication process using a thick photoresist to expose the conductive part. Each microprobe electrode was independently connected to the backside of the substrate through the silicon TGV. The single via resistance was measured to be 1.26 ± 0.041 Ω. To verify the electrochemical characteristics of the microprobe electrodes with individual interconnects, the steady-state limiting current through the redox reaction was measured by the cyclic voltammetry method for each electrode. The measured steady-state peak current of the microprobe electrode was compared with the theoretical calculation. Further, the electrode impedance was measured and the equivalent circuit analysis was constructed using the Zview impedance modeling software. Experiments were conducted to measure the impedance of 16 microprobe electrodes, and it was confirmed that the impedance did not exceed 1 MΩ at 1 kHz. Then, primary rat cortical neuron cells (DIV 7) were cultured on the fabricated microprobe electrodes and neural spike signals were successfully measured. Also, the light transmittance experiment was conducted to measure the transparency of the TGV structure fabricated through the glass reflow process.

Long Slender Piezo-Resistive Silicon Microprobes for Fast Measurements of Roughness and Mechanical Properties inside Micro-Holes with Diameters below 100 µm

During the past decade, piezo-resistive cantilever type silicon microprobes for high-speed roughness measurements inside high-aspect-ratio microstructures, like injection nozzles or critical gas nozzles have been developed. This article summarizes their metrological properties for fast roughness and shape measurements including noise, damping, tip form, tip wear, and probing forces and presents the first results on the measurement of mechanical surface parameters. Due to the small mass of the cantilever microprobes, roughness measurements at very high traverse speeds up to 15 mm/s are possible. At these high scanning speeds, considerable wear of the integrated silicon tips was observed in the past. In this paper, a new tip-testing artefact with rectangular grooves of different width was used to measure this wear and to measure the tip shape, which is needed for morphological filtering of the measured profiles and, thus, for accurate form measurements. To reduce tip wear, the integrated silicon tips were replaced by low-wear spherical diamond tips of a 2 µm radius. Currently, a compact microprobe device with an integrated feed-unit is being developed for high-speed roughness measurements on manufacturing machines. First measurements on sinusoidal artefacts were carried out successfully. Moreover, the first measurements of the elastic modulus of a polymer surface applying the contact resonance measurement principle are presented, which indicates the high potential of these microprobes for simultaneous high-speed roughness and mechanical parameter measurements.

3D piezoresistive silicon microprobes with stacked suspensions for tailored mechanical anisotropies

Different kinds of piezoresistive microprobes based on silicon have been developed to enable measurement with high accuracies. However, the typical mechanical anisotropy of such systems leads to the slip of the tip, when probing inclined surfaces. Here, a novel microprobe design is presented, which can be tailored to provide a range of anisotropy or even a perfect isotropy. In the first approach, the microprobe is composed of two stacked silicon membranes. In the second approach, a stainless steel suspension in the form of a laser structured foil is stacked on a silicon membrane. Geometrical parameter studies were carried out by mechanical FEM simulations to determine their influence on the stiffnesses in all spatial directions and to predict anisotropies. Microsystems with selected geometries were fabricated and stacking was obtained through selective adhesive transfer and bonding on a wafer level. Prototypes with anisotropies between 3 and 0.4 were characterized confirming the simulations.

High-speed microprobe for roughness measurements in high-aspect-ratio microstructures

Cantilever-type silicon microprobes with an integrated tip and a piezoresistive signal read out have successfully proven to bridge the gap between scanning force microscopy and stylus profilometry. Roughness measurements in high-aspect-ratio microstructures (HARMS) with depths down to 5 mm and widths down to 50 µm have been demonstrated. To improve the scanning speed up to 15 mm s−1, the wear of the tip has to be reduced. The atomic layer deposition (ALD) technique with alumina (Al2O3) has been tested for this purpose. Repeated wear measurements with coated and uncoated microprobe cantilevers have been carried out on a roughness standard at a speed of 15 mm s−1. The tip shape and the wear have been measured using a new probing tip reference standard containing rectangular silicon grooves with widths from 0.3 µm to 3 µm. The penetration depth of the microprobe allows one to measure the wear of the tip as well as the tip width and the opening angle of the tip. The roughness parameters obtained on the roughness standard during wear experiments agree well with the reference values measured with a calibrated stylus instrument, nevertheless a small amount of wear still is observable. Further research is necessary in order to obtain wear resistant microprobe tips for non-destructive inspection of microstructures in industry and microform measurements, for example in injection nozzles.

Optimizing Spike-Sorting Yield through Selection of Optimal Recording Sites in High-density Microelectrode Arrays

Optimizing Spike-Sorting Yield through Selection of Optimal Recording Sites in High-density Microelectrode Arrays

Optimization of a Michigan-type silicon microprobe for infrared neural stimulation

This paper presents a Michigan-type deep brain silicon optrode capable of delivering infrared light into the neural tissue. Silicon optrodes were fabricated by deep reactive ion etching (DRIE) and subsequent wet chemical polishing. The proposed method is feasible to reduce the sidewall roughness significantly and is able to turn the substrate material into an infrared waveguide of sufficient efficiency for infrared neural stimulation. The advantage of our approach is that the fabrication process is fully compatible with that of functional neural microelectrodes. Moreover, there is no need to add further waveguide layers on top of such devices aiming IR stimulation, which may induce less tissue trauma. Our design also facilitates the spatially controlled illumination of the tissue through integrated micromirrors and microlenses and the precise alignment of an optical fiber through an integrated guide slot. An average system efficiency of 22.1% with a Gaussian beam profile (NA=0.13) was achieved by reducing the RMS roughness of the sidewall down to 8.7nm using 1310nm wavelength illumination and coupled core diameter of 9μm. To our knowledge, this is the first investigation of the optical properties of a Michigan-type silicon microprobe aiming infrared neural stimulation at the substrate level.

Microscale temperature sensing using novel reliable silicon vertical microprobe array: Computation and experiment

Microscale temperature sensing using a fabricated novel vertical silicon microprobe array was investigated for the first time using a combined simulation and experimental technique. In this context, silicon microprobes were designed with 3μm in diameter and 30μm in height. These high-aspect-ratio probes are found to be effective in microscale multisite temperature sensing. The designed microprobes (p-type) were fabricated in <111> out-of-plane orientation using vapor–liquid-solid (VLS) technique on n-type silicon substrate. The temperature dependent shift in the rectifying current–voltage (I–V) curves of the embedded p–n diode was experimentally determined and the temperature sensitivity of diode was found to be −2.3mV/K at 0.1μA. A complete 3-D model of the microprobe was created and finite element (FE) method was applied to compute the sensing capability by capturing temperature distribution taking anisotropic and phonon scattering effects on thermal conductivity of silicon into account. The obtained computational result on microscale temperature sensitivity has shown a similar trend of experimental findings. FE simulation thus can serve as a tool to a-priori predict temperature sensing capabilities of microprobes used in many applications such as artificial electronic fingertips of robotic hand/prosthetics, biological soft samples.

Brain activity mapping at multiple scales with silicon microprobes containing 1,024 electrodes.

The coordinated activity of neural ensembles across multiple interconnected regions has been challenging to study in the mammalian brain with cellular resolution using conventional recording tools. For instance, neural systems regulating learned behaviors often encompass multiple distinct structures that span the brain. To address this challenge we developed a three-dimensional (3D) silicon microprobe capable of simultaneously measuring extracellular spike and local field potential activity from 1,024 electrodes. The microprobe geometry can be precisely configured during assembly to target virtually any combination of four spatially distinct neuroanatomical planes. Here we report on the operation of such a device built for high-throughput monitoring of neural signals in the orbitofrontal cortex and several nuclei in the basal ganglia. We perform analysis on systems-level dynamics and correlations during periods of conditioned behavioral responding and rest, demonstrating the technology's ability to reveal functional organization at multiple scales in parallel in the mouse brain.

Experimental study on the mechanical interaction between silicon neural microprobes and rat dura mater during insertion.

In vivo insertion experiments are essential to optimize novel neural implants. Our work focuses on the interaction between intact dura mater of rats and as-fabricated single-shaft silicon microprobes realized by deep reactive ion etching. Implantation parameters like penetration force and dimpling through intact dura mater were studied as a function of insertion speed, microprobe cross-section, tip angle and animal age. To reduce tissue resistance, we proposed a unique tip sharpening technique, which was also evaluated in in vivo insertion tests. By doubling the insertion speed (between 1.2 and 10.5 mm/min), an increase of 10-35% in penetration forces was measured. When decreasing the cross-section of the microprobes, penetration forces and dimpling was reduced by as much as 30-50% at constant insertion speeds. Force was noticed to gradually decrease by decreasing tip angles. Measured penetration forces through dura mater were reduced even down to 11±3 mN compared to unsharpened (49±13 mN) probes by utilizing our unique tip sharpening technique, which is very close to exerted penetration force in the case of retracted dura (5±1.5 mN). Our findings imply that age remarkably alters the elasticity of intact dura mater. The decreasing stiffness of dura mater results in a significant rise in penetration force and decrease in dimpling. Our work is the first in vivo comparative study on microelectrode penetration through intact and retracted dura mater.

Integration of a silicon-based microprobe into a gear measuring instrument for accurate measurement of micro gears

The integration of silicon micro probing systems into conventional gear measuring instruments (GMIs) allows fully automated measurements of external involute micro spur gears of normal modules smaller than 1 mm. This system, based on a silicon microprobe, has been developed and manufactured at the Institute for Microtechnology of the Technische Universität Braunschweig. The microprobe consists of a silicon sensor element and a stylus which is oriented perpendicularly to the sensor. The sensor is fabricated by means of silicon bulk micromachining. Its small dimensions of 6.5 mm × 6.5 mm allow compact mounting in a cartridge to facilitate the integration into a GMI. In this way, tactile measurements of 3D microstructures can be realized. To enable three-dimensional measurements with marginal forces, four Wheatstone bridges are built with diffused piezoresistors on the membrane of the sensor. On the reverse of the membrane, the stylus is glued perpendicularly to the sensor on a boss to transmit the probing forces to the sensor element during measurements. Sphere diameters smaller than 300 µm and shaft lengths of 5 mm as well as measurement forces from 10 µN enable the measurements of 3D microstructures. Such micro probing systems can be integrated into universal coordinate measuring machines and also into GMIs to extend their field of application. Practical measurements were carried out at the Physikalisch-Technische Bundesanstalt by qualifying the microprobes on a calibrated reference sphere to determine their sensitivity and their physical dimensions in volume. Following that, profile and helix measurements were carried out on a gear measurement standard with a module of 1 mm. The comparison of the measurements shows good agreement between the measurement values and the calibrated values. This result is a promising basis for the realization of smaller probe diameters for the tactile measurement of micro gears with smaller modules.

Multisite monitoring of choline using biosensor microprobe arrays in combination with CMOS circuitry

A miniature device enabling parallel in vivo detection of the neurotransmitter choline in multiple brain regions of freely behaving rodents is presented. This is achieved by combining a biosensor microprobe array with a custom-developed CMOS chip. Each silicon microprobe comprises multiple platinum electrodes that are coated with an enzymatic membrane and a permselective layer for selective detection of choline. The biosensors, based on the principle of amperometric detection, exhibit a sensitivity of 157±35 µA mM(-1) cm(-2), a limit of detection of below 1 µM, and a response time in the range of 1 s. With on-chip digitalization and multiplexing, parallel recordings can be performed at a high signal-to-noise ratio with minimal space requirements and with substantial reduction of external signal interference. The layout of the integrated circuitry allows for versatile configuration of the current range and can, therefore, also be used for functionalization of the electrodes before use. The result is a compact, highly integrated system, very convenient for on-site measurements.

CMOS-Based High-Density Silicon Microprobe Arrays for Electronic Depth Control in Intracortical Neural Recording–Characterization and Application

This paper reports on the characterization and intracortical recording performance of high-density complementary-metal-oxide-semiconductor (CMOS)-based silicon microprobe arrays. They comprise multiplexing units integrated on the probe shafts being part of the signal transmission path. Their electrical characterization reveals a negligible contribution on the electrode impedances of 139 ±11 kΩ and 1.2 ±0.1 MΩ and on the crosstalks of 0.12% and 0.98% for iridium oxide ( IrOx) and platinum (Pt) electrodes, respectively. The power consumption of the single-shaft probe was found to be 57.5 μW during electrode selection. The noise voltage of the switches was determined to be 5.6 nV/√Hz; it does not measurably affect the probe performance. The recording selectivity of the electrode array is demonstrated by electrical potential measurements in saline solution while injecting a stimulating current using an external probe. In-vivo recordings in anesthetized rats using all 188 electrodes with a pitch of 40.7 μm are presented and analyzed in terms of single neural activity and signal-to-noise ratio. The concept of electronic depth control is proven by performing mechanical translation of the probe shaft while electronically switching to adjacent electrodes to compensate the mechanical shift.

Fracture analysis of silicon microprobes designed for deep-brain stimulation

Recent progress in microtechnology has made room for novel applications in neural stimulation as well as for extending our knowledge on several malfunction of the nerval system such as tremor, epilepsy or Parkinson's disease, which belong to the most serious medical issues in the population of developed countries. Integrated drug delivery function in neural implants can contribute advantageously to the long-term stability of the medical devices in brain tissue. In our work, a hollow silicon microprobe developed for deep-brain application is proposed and tested. The fabrication is based on a novel micromachining technique utilising conventional MEMS technology and integrating both the probe shaft and microchannel system into the same substrate. The integrated microchannels have major influence on the failure properties of the probe, therefore the feasibility of the realised microstructures for deep-brain stimulation is characterised by experimental method and by modeling focusing on the change in mechanical response to axial loading.

On the Fabrication Parameters of Buried Microchannels Integrated in In-Plane Silicon Microprobes

This paper aims the characterization of buried microchannels in silicon realized by deep reactive ion etching. The effects of dry etching parameters on the integrability into hollow microprobes are thoroughly investigated from both technological and functional aspects. Results are supposed to give physiology related probe designers a deeper insight into microfabrication-related issues.

An intra-cerebral drug delivery system for freely moving animals

Microinfusions of drugs directly into the central nervous system of awake animals represent a widely used means of unravelling brain functions related to behaviour. However, current approaches generally use tethered liquid infusion systems and a syringe pump to deliver drugs into the brain, which often interfere with behaviour. We address this shortfall with a miniaturised electronically-controlled drug delivery system (20 × 17.5 × 5 mm³) designed to be skull-mounted in rats. The device features a micropump connected to two 8-mm-long silicon microprobes with a cross section of 250 × 250 μm² and integrated fluid microchannels. Using an external electronic control unit, the device allows infusion of 16 metered doses (0.25 μL each, 8 per silicon shaft). Each dosage requires 3.375 Ws of electrical power making the device additionally compatible with state-of-the-art wireless headstages. A dosage precision of 0.25 ± 0.01 μL was determined in vitro before in vivo tests were carried out in awake rats. No passive leakage from the loaded devices into the brain could be detected using methylene blue dye. Finally, the device was used to investigate the effects of the NMDA-receptor antagonist 3-((R)-2-Carboxypiperazin-4-yl)-propyl-1-phosphonic acid, (R)-CPP, administered directly into the prefrontal cortex of rats during performance on a task to assess visual attention and impulsivity. In agreement with previous findings using conventional tethered infusion systems, acute (R)-CPP administration produced a marked increase in impulsivity.