Field of the Invention
The present invention relates to a technology for fabricating a nanowire field-effect sensor, and more particularly, to a nanowire field-effect sensor including nanowires having a network structure and to a fabrication method, in which a bulk silicon substrate is used so that the fabrication cost of the sensor can be reduced and the integration density of the sensor can be increased, and a nano-network is effectively insulated so that the high sensitivity and structural stability of the sensor can be ensured.
Description of the Prior Art
An electrochemical sensor is a device that converts a physical or biochemical signal from a target material to be detected into an electrical signal, and is characterized by having a small size and a high detection speed, compared to conventional fluorescent sensors. Such electrochemical sensors are expected to be widely used in applications, including biosensors, chemical sensors and environmental sensors, depending on the kind of target material.
The electrochemical sensor includes a receptor material that selectively reacts with a target material, a buffer solution and a submerged gate electrode, and is operated in a solution, unlike a field effect transistor that is an electronic element. For this reason, it is important to minimize current leakage from the electrochemical sensor. In the electrochemical sensor, a detector material that selectively binds to a target material in order to detect the target material is fixed to the detection surface of the sensor through a series of chemical treatments. When the charged target material reacts with and binds to the receptor material on the detection surface, the electrical conductivity in the channel of the sensor is changed by the charge of the target material, and the target material can be detected by observing this change in the electrical conductivity of the sensor. The target material bound to the receptor material fixed to the detection surface by a chemical reaction is not easy to separate, and the fixed receptor material is difficult to reuse after its separation from the detection surface. In addition, if the sensor is continuously used, the characteristics of the sensor, such as sensitivity, will be deteriorated. For this reason, a sensor for application to a product should be used in a disposable manner without being reused. To commercialize an electrochemical sensor as a product, cost effectiveness and the ease of integration are important, in addition to characteristics such as high sensitivity, high specificity and fast response-time.
Among electrochemical sensors, a field-effect sensor with nanowires is attracting attention due to its high sensitivity and selectivity and fast response time. The nanowire structure has excellent gate control ability due to its high area-to-volume ratio, and for this reason, shows a great change in electrical conductivity even when the change in the charge of a target material by the detection surface is small, indicating that the nanowire structure shows high sensitivity. In addition, because the field-effect sensor can detect a target material in real time by an electrical measurement method, it can be produced in large amounts using existing CMOS semiconductor process technology.
FIG. 1A illustrates the structure of a nanowire field-effect transistor including a silicon-on-insulator (SOI) substrate according to the prior art, and FIG. 1B is a cross-sectional view taken along line A-A of FIG. 1A.
Referring to FIGS. 1A and 1B, an SOI substrate 11 and a bottom insulating layer 12 are sequentially deposited, and then a source electrode region 13S and a drain electrode region 13D are formed on both sides of the bottom insulating layer 12 so as to be opposite to each other, and nanowires 14 having a gate insulating layer applied thereto are connected between the two electrode regions 13S and 13D.
A detector material 18A is attached to the nanowires 14, and a target material 18B is selectively attached to the detector material 18A. In this case, the electrical conductivity of the nanowire channel region is changed by the charge of the target material 18B, and the nanowire field-effect sensor detects this change in the electrical conductivity and outputs the result of detection. Herein, the electric potential of a solution that is filled in the nanowire channel region can be fixed using a separate submerged gate electrode 19.
The nanowire field-effect sensor according to the prior art as described above uses an SOI wafer as a substrate, and has a structure in which the top silicon layer is completely isolated from the substrate by the bottom insulating layer. To form the one-dimensional nanowires as described above, an element is fabricated on the expensive SOI substrate, and for this reason, the nanowire field-effect sensor has a problem in that it is costly. For reference, the price of an SOI substrate having a thin top silicon layer, which is used to form nanowires, is at least 20 times higher than the price of a bulk silicon substrate. In addition, because it is impossible to reuse a receptor material and a target material, which are used for detection in the nanowire field-effect sensor that is a biosensor, the nanowire field-effect sensor according to the prior art has a problem in that many maintenance costs are incurred.
Furthermore, in the case in which nanowires equal or similar to those used in the nanowire field-effect sensor according to the prior art are used, the sensitivity of the sensor itself is very high, but there is a shortcoming in that the area of the nanowire is very small (several square nanometers to several square microns), and thus the amount of target material that is transferred from the buffer solution to the detection surface is necessarily very limited, indicating that the sensor has low sensitivity.
In addition, in the case of the nanowire field-effect sensor according to the prior art, the nanowires to which the detector material is fixed can be formed by a bottom-up or top-down method. In the case of the bottom-up method, nanowires formed using a semiconductor processing technique such as CVD (chemical vapor deposition) are arranged at specific positions to thereby fabricate a sensor, and thus the synthesis and arrangement of the nanowires are not easy, making it difficult to produce the sensor in large amounts.