Can negative rates be sustainable?

The yield of the Swiss government bond with up to 20 years maturity falls into the negative zone, which means that bond investors are paying the Swiss government to lend it money. Moreover, many banks are taking action to charge negative saving interest rates on the big companies which hold lots of cash in their accounts. From here, we can see that lenders (savers) are paying to lend their money and borrowers are paid to be lent. Is this a stable equilibrium that the demand and supply of loans are equal and both borrowers and lenders are not willing to take different actions?

When borrowers are paid to borrow, of course they would like to keep borrowing as borrowing can help them generate profits. However, it is not necessary for lenders to keep paying to lend money to the others. First of all, lending involves risk, with a negative interest rate, the risk becomes even greater. The government bond yield falls below zero because the government bond is often considered as a risk free security; once the environmental risk or the exogenous risk becomes too great to invest in any other securities that involve risk. Therefore, under such circumstances, banks and investors will never choose to lend to any borrower who is considered to be risky, the only lending target will be the risk free clients, which are governments and large international firms.

Therefore, it is not even considered as an equilibrium that at the current low rates, there are some unsafe potential borrowers who are willing to borrow, but are not able to borrow from the institutes because they are considered to be risky. Moreover, when the market environmental risk changes, the action of lending will also change, that if risk increases, the interest rate could fall deeper in the negative zone, if risk reduces, the interest rate will increase and become positive again.