zener - Protecting against over voltage but with minimum leakage current

I have a circuit where I sense an input which is a voltage divider with resistor.

Since the voltage divider needs to have high impedance, the current flowing through is in the range of 10's of uA.

I need to protect the the analog input so that the voltage doesn't exceed 5V. Maximum range is 200mV (so clamping anywhere between 250mV to 5V is acceptable).

The first choice would be a Zener diode, but the problem is the reverse leakage current of those starts at in the 1uA range, which would induce an error to the measurement.

Maximum allowable current leakage is 25nA.

I thought of using a regular diode in forward mode but they also leak below the conductive threshold.

Is there any other clever way to clamp over voltage while having minimum leakage current ?

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EDIT

Is this solution a viable idea ? Transistor have a CE leakage in the nA range, cascading 2 allows to increase the voltage.

^{simulate this circuit – Schematic created using CircuitLab}

The simulation give a leakage current of 14pA at 200mV at the resistor node.

Answer

You can use a FET transistor like Siliconix 2N4117A or similar device. This kind of diode has a very low leakage current.

^{simulate this circuit – Schematic created using CircuitLab}

Then you clamp the input signal

^{simulate this circuit}

The next circuit is a low leakage clamp + input current limiter. NOTE: The circuit example by Analog Devices says that input transitors (current limit) are depletion mode P-ch JFET, but they depicted them as I did. You have to contact the author of this circuit to get the correct version of it.

^{simulate this circuit}

Reference:

Analog devices

Burr-Brown