Patent Application
20140300340
1. Technical Field
The present disclosure relates to human blood gas sensing and, more specifically, to a device structure for human blood gas sensing having a high-k metal gate.
2. Discussion of Related Art
Partial pressure of oxygen in the blood (pO2) is an essential parameter in evaluating the oxygenation status of patients. Effectively measuring pO2 may provide insight into how efficiently the patient's lungs are delivering oxygen into the blood. For this reason, pO2 is carefully monitored for patients in critical condition, such as those in a hospital intensive care unit (ICU), neonatal intensive care unit (NICU), emergency room/department, etc,
Traditional pO2 sensors make use of the Clark principal, which utilized electrochemical oxygen analyzers that measure electrochemical reduction of oxygen by measuring oxygen tension amperometrically at a negatively polarized electrode, known as the “Clark” electrode.
These existing approaches for pO2 sensing may be sensitive to storage conditions such as temperature and humidity, may have a short shelf time, and may have a relatively high cost associated with their use owing to the expensive analysis machines that are generally used.
A device structure for detecting partial pressure of oxygen in blood includes a semiconductor substrate including a source region and a drain region. A multi-layer gate structure is formed on the semiconductor substrate. The multi-layer gate structure includes an oxide layer formed over the semiconductor substrate, a high-k layer formed over the oxide layer, a metal gate layer formed over the high-k layer, and a polysilicon layer formed over the metal gate layer. A receiving area holds a blood sample in contact with the multi-layer gate structure. The high-k layer is exposed to contact the blood sample in the receiving area.
Conductive connectors may be formed over the source and drain regions of the semiconductor substrate for applying a voltage to the source and drain regions of the semiconductor substrate therethrough and to measure a current shift resulting from the presence of the blood sample in the receiving area.
Gate terminals may be formed on the multi-layer gate structure for driving a current through the metal gate layer to provide annealing to the blood sample in the receiving area.
The multi-layer gate structure may be a common gate structure formed over a plurality of semiconductor substrates that are each similar or identical to the semiconductor substrate. The common gate structure may have a comb structure on at least one end thereof for increasing a contact area between the high-k layer and the blood sample in the receiving area.
The semiconductor substrate may further include a conducting channel between the source and drain regions, the multi-layer gate structure formed over the conducting channel. The source region, the drain region, and the conducting channel may be formed from a N/P/N field effect transistor formed in the semiconductor substrate.
The oxide layer may include silicon dioxide. The oxide layer may be substantially 0.05 μm thick. The high-k layer may include hafnium (IV) oxide (HfO2). The high-k layer may be substantially 0.05 μm thick.
The metal gate layer may include titanium nitride (TiN). The metal gate layer may be substantially 0.1 μm thick.
A plurality of conductive connectors may be formed over the silicon substrate, on opposite sides of the multi-layer gate structure, and they may make contact with the source and drain regions, respectively. Each of the plurality of conductive connectors may include tungsten. Each of the plurality of conductive connectors may be substantially 0.5 μm thick. Each of the plurality of conductive connectors may be formed over a respective nickel silicon (NiSi) contact formed in the semiconductor substrate.
Opposite sides of the multi-layer gate structure may each be spaced apart from a nearest conductive connector of the plurality of conductive connectors by substantially 0.5 μm. The multi-layer gate structure may be substantially 1 μm wide.
A porous membrane layer may be formed over the multi-layer gate structure. The porous membrane layer may include a plurality of pores, each of which is substantially 1 μm wide.
A method for fabricating a device structure for detecting partial pressure of oxygen in blood includes forming a multi-layer gate structure on a semiconductor substrate by forming an oxide layer over the semiconductor substrate, forming a high-k layer formed over the oxide layer, forming a metal gate layer formed over the high-k layer, and forming a polysilicon layer formed over the metal gate layer. A spacer may be formed on opposite sides of the multi-layer gate structure. A source region and a drain region may be formed within the silicon substrate by implanting impurities therein after the spacer has been formed. The spacer is removed after the source and drain regions have been formed.
Conductive connectors may be formed over the source and drain regions of the semiconductor substrate for applying a voltage to the source and drain regions of the semiconductor substrate therethrough and to measure a current shift resulting from the presence of the blood sample in the receiving area.
Gate terminals may be formed on the multi-layer gate structure for driving a current through the metal gate layer to provide annealing to the blood sample in the receiving area.
The multi-layer gate structure may be a common gate structure formed over a plurality of semiconductor substrates that are each similar or identical to the semiconductor substrate. The common gate structure may have a comb structure on at least one end thereof for increasing a contact area between the high-k layer and the blood sample in the receiving area.
The semiconductor substrate may further include a conducting channel between the source and drain regions, the multi-layer gate structure formed over the conducting channel. The source region, the drain region, and the conducting channel may be formed from a N/P/N field effect transistor formed in the semiconductor substrate.
The oxide layer may be formed comprising silicon dioxide. The oxide layer may be formed with a thickness of substantially 0.05 μm.
The high-k layer may be formed comprising hafnium (IV) oxide (HfO2). The high-k layer may be formed with a thickness of substantially 0.05 μm.
The metal gate layer may be formed comprising titanium nitride (TiN). The metal gate layer may be formed with a thickness of substantially 0.1 μm.
A plurality of conductive connectors may be formed over the silicon substrate, on opposite sides of the multi-layer gate structure, making contact with the source and drain regions, respectively. Each of the plurality of conductive connectors may be formed including tungsten.
Each of the plurality of conductive connectors may be formed having a thickness of substantially 0.5 μm.
Each of the plurality of conductive connectors may be formed over a respective nickel silicon (NiSi) contact formed in the semiconductor substrate.
Opposite sides of the multi-layer gate structure are each formed to be spaced apart from a nearest conductive connector of the plurality of conductive connectors by substantially 0.5 μm.
The multi-layer gate structure may be formed having a width of substantially 1 μm. A porous membrane layer may be formed over the multi-layer gate structure. The multi-layer gate structure may be formed using deposition, lithography, or reactive-ion etching (RIE). The spacer may be formed using deposition or reactive-ion etching (RIE).
The spacer may be removed using reactive-ion etching (RIE). The source and drain regions and the metal gate layer may each be formed using lithography, deposition, or annealing.
A method for testing partial pressure of oxygen within blood includes applying a blood sample to make contact with a multi-layer gate structure formed on a semiconductor substrate. The multi-layer gate structure includes an oxide layer formed over the semiconductor substrate, a high-k layer formed over the oxide layer, a metal gate layer formed over the high-k layer, and a polysilicon layer formed over the metal gate layer. A current is sent though the metal gate later to obtain a desired temperature within the multi-layer gate structure. A first voltage is applied to the source, a second voltage to the drain and a third voltage to the multi-layer gate structure to create a current therethrough. A shift in the current is measured through the multi-layer gate structure. A partial pressure of oxygen in the blood sample is determined based on the measured current shift.
The first and second voltages may be applied to the source and drain via conductive connectors formed thereon. The multi-layer gate structure may be a common gate structure formed over a plurality of semiconductor substrates that are each similar or identical to the semiconductor substrate. The common gate structure may have a comb structure on at least one end thereof for increasing a contact area between the high-k layer and the blood sample applied to the multi-layer gate structure.
A more complete appreciation of the present disclosure and many of the attendant aspects thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing exemplary embodiments of the present disclosure illustrated in the drawings, specific terminology is employed for sake of clarity. However, the present disclosure is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents which operate in a similar manner.
Exemplary embodiments of the present invention provide a device and approach for measuring partial pressure of oxygen in the blood (pO2) that may be less sensitive to storage conditions, may have a longer shelf time, and may be implemented at a lower cost than conventional approaches. Additionally, exemplary embodiments of the present invention may be made small enough for portable and/or home use and may be integrated into existing biosensor chip devices such as the EPOC BGEM blood gas and electrolyte card provided by ALERE.
Exemplary embodiments of the present invention relate to the fabrication and use of a field effect transistor (FET) having a gate structure including a high-k material such as Hafnium Oxide (HfO2) which may be very sensitive to oxygen concentration. The high-k metal gate FET may also have a spacer removed to expose a perimeter of the gate oxide for stronger sensitivity. The pO2 sensing device may include multiple high-k metal gate FETs. A blood sample may be dropped on or made to flow through patterned array elements to bring the sample to an anneal temperature to shift the temperature-sensitive flatband voltage (Vfb) and to drive current for sensing oxygen partial pressure.
In
The multi-layer gate stack may include a silicon dioxide (SiO2) layer 109 over the substrate 101. The SiO2layer 109 may be, for example, approximately 0.05 μm thick. Above the SiO2 layer 109 may be a high-k layer 108. The high-k layer may include, for example, hafnium (IV) oxide (HfO2). The high-k layer 108 may be, for example, approximately 0.05 μm thick. The high-k layer 108 may include a material that has a dielectric constant greater than that of silicon dioxide.
Thereabove may be a metal gate layer (107), which may include, for example titanium nitride (TiN), may be formed. The metal gate layer (107) may be, for example, approximately 0.1 μm thick. On top of the metal gate later (107) a polysilicon layer (106) may be formed.
The conductive connectors 112 and 113 may be made of a conductive material such as tungsten. The conductive connectors 112 and 113 have thicknesses 115, that may be, for example, approximately 0.5 μm Under the conductive connectors 112 and 113, and located within the substrate 101 may be nickel silicon (NiSi) contacts 120 and 121. The NiSi contacts may facilitate electrical connection to the source and drain 102 and 104, respectively, and may be formed, for example, by annealing Nickel on top of the silicon substrate 101.
The gate stack, and in particular, the polysilicon layer 106, may be spaced apart from the conductive connectors 112 and 113 by distances 117 and 119, which may be, for example, approximately 0.5 μm. The width of the gate stack, and in particular, the polysilicon layer 106 is width 118 and this width may be, for example, approximately 1 μm.
Above the gate stack, and in particular, the polysilicon layer 106, may be a filter 114. The filter may include a set of pores for allowing blood to flow therethrough while filtering the blood cells and platelets as well as any other unwanted substances. The filter layer may have pores of a size of, for example, 1 μm.
In operation, oxygen from the blood may fill the vacancy states of the high-k layer 108 and this may cause a shift in the flatband voltage with respect to temperature (Vt). The degree of the shift in Vt may be influenced by the partial pressure of oxygen. As the diffusion of oxygen may stabilize within seconds, the Vt shift may be determined by monitoring the current across the source and drain 102 and 104 before and after the diffusion of the oxygen from the blood sample, given a constant gate/drain voltage.
In the top-down planar view of
As the flatband voltage is temperature sensitive, the pO2 sensing device 200 may provide for thermal annealing so that the temperature may be accurately controlled. Exemplary embodiments of the present invention may provide for in-situ thermal annealing by applying voltage through two gate terminals to result in local self-heating. Application of the voltage to result in local self-heating may be performed, for example, by applying a high current through the metal gate layer 107 through contacts disposed on the gate layer. As discussed above, the metal gate layer, which may include TiN, may have a thermal conductivity of approximately 40 W/(mk), a thermal resistance of approximately 6.25×104, assuming a TiN layer 0.4 μm wide, 0.04 μm thick and 0.04 μm long. Accordingly, the high current for providing heating may be on the order of 1×10 −2 W if applying 1V across the TiN layer. Under such a current, the temperature increase may be as high as approximately 625K.
Exemplary embodiments of the present invention may utilize a two-step approach for detecting pO2 using the pO2 sensing device described above. First, a voltage may be applied on the gate terminals to perform annealing so that a desired temperature may be obtained. Then, voltage may be applied on the gate, source, and drain to measure current shift for sensing pO2. The pO2 may be calculated from the current shift before and after the diffusion of oxygen from the blood into the high-k layer as the current shifts caused by various oxygen levels may be known for the given temperature.
Exemplary embodiments described herein are illustrative, and many variations can be introduced without departing from the spirit of the disclosure or from the scope of the appended claims. For example, elements and/or features of different exemplary embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.
