Micrometer Scale Silicon Dioxide Tunnels for On-chip Fluidic Sample Delivery to Nanometer-scale Chemical Sensors
- PDF / 1,826,516 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 204 Views
J9.1.1
Micrometer Scale Silicon Dioxide Tunnels for On-chip Fluidic Sample Delivery to Nanometer-scale Chemical Sensors Ali Gokirmak and Sandip Tiwari School of Electrical and Computer Engineering, Cornell University, Ithaca NY 14853, U.S.A. ABSTRACT We have developed a low temperature, CMOS compatible back-end-of-the-line process of making micrometer scale silicon dioxide tunnels for fluidic sample delivery to nanometer scale CMOS based chemical sensors. The fabrication process for these tunnels involve deposition of silicon dioxide over sacrificial photoresist and removal of the sacrificial resist from small holes opened on the top surface. The fabrication process allows arbitrary tunnel widths, about one micrometer and larger, if the supporting pillars are used. The highest process temperature is 135 C. The fabricated structures are compatible with cleaning steps in strong base or acid solutions and can withstand anneal steps at higher temperatures. It is possible to implement complicated, multilevel chemical sensor and mixer networks where microfluidic tunnels cross over each other by repeating the fabrication sequence. INTRODUCTION Field effect transistors (FETs) are three terminal devices where the current between the source and the drain is controlled by a gate potential [1]. FETs have been mainly used as logic devices and amplifiers in integrated circuits but they have found a number of other uses as chemical and mechanical sensors. Variations in surface charge, dielectric constant and the separation between the gate and the channel of an FET results in a change in the source-drain current [2,3]. Using the semiconductor technology it is possible to make very small FETs [1,4,5]. These nanometer-scale structures, fabricated on silicon substrates, can be tailored to form FET-based chemical sensors for very fast sensing with high spatial resolution. Use of these very small scale sensors requires a system to deliver the sample from an outside source into the sensor on a chip. In order to interface an external pluming system with the on-chip sensors, on-chip microfluidic tunnels are needed to bring the sample from one end of the chip into the nano-fluidic sensors and to take the sample out (Fig. 1). For FET based sensors the delivery tunnels have to be electrically isolated from the devices. The microfluidic tunnels must be large enough to allow the necessary throughput. These tunnels can either be monolithically integrated with the sensors, where the sensors and the tunnels are fabricated together, or the tunnels can be fabricated after the fabrication process of the sensors in a backend-of-the-line integration fashion. In both approaches there are materials, process and
J9.1.2
in
out
6 µm h=10nm
1 µm
Data Loading...
