Microfabrication of a mechanically controllable break junction in silicon

Abstract

We present a detailed description of the fabrication and operation at room temperature of a novel type of tunnel displacement transducer. Instead of a feedback system it relies on a large reduction factor assuring an inherently stable device. Stability measurements in the tunnel regime infer an electrode stability within 3 pm in a 1 kHz bandwidth. In the contact regime the conductance takes on a discrete number of values when the constriction is reduced atom by atom. This reflects the conduction through discrete channels. © 1995 American Institute of Physics.Micromachining in silicon is an ongoing effort to provide ever smaller devices used as the active part of a sensor. Currently, it is straightforward to produce suspended beams, small springs, and vibrating or rotating structures on a chip. Engineers can make use of a number of classical transducer phenomena, such as piezoelectricity, piezoresistivity and capacitance changes to convert displacements into an electrical signal. However, the formation of smaller sensors is often obtained at the cost of precision, since the signal of the above mentioned transducer phenomena scale with size. In contrast to classical transducers, a tunnel transducer 1 ͑e.g., an STM͒ is compatible with further miniaturization and possesses an astonishing sensitivity to displacements. When a vacuum tunnel gap between two metallic electrodes is increased by 1 Å, the tunnel resistance increases approximately by an order of magnitude. This has been realized by a number of groups who have used tunnel sensors in devices.2 The extreme sensitivity of these sensors on positional displacements however implies that the practical range of operation is limited to distances smaller than 5 Å since at larger distances the resistance becomes almost infinite and unmeasurable.In conventional STM embodiments, one electrode is usually mounted on a flexible lever, which can be moved by an electrical signal. The tunnel gap is kept constant with the use of a feedback system, necessary since temperature fluctuations, ͑acoustic͒ vibrations or other disturbances will otherwise change the vacuum gap over distances much larger than the practical range. An accelerometer, magnetometer, and an infrared sensor have been successfully developed with these kind of tunnel sensors in feedback operation. 2Despite these successes we have used a different approach and constructed an inherently stable tunnel sensor. When used as a displacement sensor this device can be fabricated in such a way that the electrode separation during operation remains in the practical range of about 5 Å. Due to the extreme stability of this device it can be operated without feedback; however it may also be used in a feedback loop. In this letter we present the fabrication and operation of this new type of tunnel sensor which was proposed in Ref. 3. It is inherently stable, adjustable, and compatible with silicon technology. Detailed measurements are shown, in both the contact and tunnel regimes.The principle of operation and a schematic perspec...

Nanogap Electrodes

“…MCB junctions are widely used for singlemolecule, even single-atom devices including one-atom metallic point contacts [42][43][44][45][46][47][48][49][50] and metal-molecule-metal junctions. [28,33,41,[51][52][53][54][55][56][57] van Ruitenbeek et al [42][43][44][45][46][47][48][49] work distinguishably in this field, especially on making atomic size contacts and tunnel junctions.…”

Atomic configuration, conductance, and tensile force of platinum wires of single-atom width

“…The formation process of ASWs during thinning of NCs has been investigated in relation to their quantized conductance defined by a quantum ͑G 0 =2e 2 / h, where e is the electron charge and h is Planck's constant͒. [16][17][18][19][20][21][22][23][24][25][26] The histograms of conductance values measured during the thinning process of NCs are produced to examine both the quantization of conductance and corresponding structures. In the conductance histograms of Au NCs, peaks are observed at integer multiples of G 0 .…”

Electron Transport in Magnetic Quantum Point Contacts

“…a differential screw). The metal to be studied is fixed on top of the flexible substrate; this can be done by simply gluing a notched wire [3,32] onto the sample or by using a microfabricated metal film [40,41]. The vertical motion of the pushing rod ( dz), which is bending the substrate, leads to a horizontal displacement of the electrodes (du).…”